最終報告書 平成24年 3 月 日本船舶海洋工学会 摩擦抵抗低減研究委員会 まえがき 日本船舶海洋工学会摩擦抵抗低減研究委員会 委員長 大阪大学 戸田保幸 摩擦抵抗低減研究委員会(略称S7委員会)は、26 期国際試験水槽会議(ITTC)に設置され 表面処理に関する専門家委員会(Specialist Committee on Surface Treatment、以下 ITTC 委 員会)の活動に対応する委員会として、日本船舶海洋工学会に設置されたストラテジー委員会で、 平成 21 年度より 3 年間活動してきました。目的は「摩擦抵抗低減法に関しての実船性能推定手 法など、今後利用される可能性のあるペイント・空気潤滑などによる摩擦抵抗低減技術、および 模型試験等に基づく摩擦抵抗推定法に関する共同研究を実施すること」としておりましたが、共 同研究は行わず、これまでの研究をまとめて、新しい塗膜などに対してどのような推定法を作れ ばよいのかなどを討議してきました。 本委員会では、ITTC 委員会の日本からの委員をサポートするのが大きな目的であることから、 表面処理による摩擦抵抗等を推定、低減する技術に関する文献調査及び表面処理による摩擦抵抗 等を推定、低減する技術に関するレビューと理論的検討を行った。前者については昨年約 80 編 の文献について、その概要を英和両文で1編あたり1ページの体裁で要約集としてとりまとめ、 「塗膜、汚損等の表面摩擦抵抗に関する文献調査集」を印刷、製本し配布しました。後者につい ての各委員からの発表資料を取りまとめたものが今回の最終報告書です。 後者の活動を紹介いたしますと委員会は摩擦抵抗に対して大きな低減効果がある空気潤滑法 等は取り扱わず、ITTC 委員会との関連から主に塗膜面の摩擦抵抗を調査しました。ただし摩擦 抵抗変化により伴流係数が変化するなどは共通のことであるのでこの委員会でも検討すること になりました。内容は塗膜面の試験法としてどのようなものがあるかを調査し、回転円筒を用い た計測、パイプによる計測、平板による試験、数式船型を用いた曳航試験など試験可能なレイノ ルズ数範囲とこれらの試験で得られた結果から高いレイノルズ数の実船相当の抵抗を推定する 方法を調査検討してきました。その中には最近開発された海上技術安全研究所の高精度な平行平 板を用いた手法も紹介されました。また表面の性質(たとえば幾何学的な粗度と流体力学的に考 察しやすい等価な砂粗度など)が分かったとしてそれをどのように使っての実船の性能推定等に ついても検討しました。また粘性抵抗変化によりプロペラ面平均流速推定法も変える必要がある こと、相関としてのΔCF と表面状況によるものの分離などが話し合われています。しかしなか なか一致した方法が提案できる状況までは至っておりませんが、いくつかの考え方が資料で示さ れています。またこの委員会のあと共同研究を行うプロジェクト委員会についても話し合いがも たれましたが、全機関が参加できるものはなかなか難しいという結論となりました。たとえば粗 度に関するデータベースを作るという提案に対しても各機関計測は行いたいが、公表してデータ を共有することには参加しにくいというものなどどうしても集まっていただいたすべての機関 がデータを共有するようなプロジェクトは難しく、実船のさまざまな計測手法などであれば共同 開発可能であろうかということで新しいプロジェクト研究委員会の提案を行わないまま、ストラ テジー研究員会(S7委員会)の活動を終わることになりました。研究活動としては半ばという 感じですがこの資料集が今後のこの分野の研究を行う方々への一助となれば幸いです。 これまで活動としては、下記の表に示すように 3 年間で 10 回の会合を持ち、各委員からの資 料に対して検討を行ってまいりました。この報告書にのせたもの以外にも各委員から発表がなさ 1 れましたが、一部は図のみであったりしたため省略させていただきました。また造船各社からの 委員には、実船摩擦抵抗推定に関し多くの有益な意見をいただきました。最後に委員名簿と、こ れまでオブザーバーとして討論に参加していただいた方々の名簿を示します。 委員会開催履歴 第1回 2009/06/09 広島大学学士会館 8名 第2回 2009/11/14 大阪大学 大学院工学研究科船舶海洋部門 10 名 第3回 2010/01/21 日本船舶海洋工学会事務局会議室 10 名 第4回 2010/04/16 日本船舶海洋工学会事務局会議室 7名 第5回 第6回 第7回 第8回 第9回 第 10 回 2010/06/25 2010/10/08 2011/01/21 2011/04/22 2011/09/16 2011/12/09 大阪大学 大学院工学研究科船舶海洋部門 日本船舶海洋工学会事務局会議室 日本船舶海洋工学会事務局会議室 日本船舶海洋工学会事務局会議室 大阪大学大学院工学研究科船舶海洋部門 日本船舶海洋工学会事務局会議室 9名 8名 7名 9名 12 名 10 名 委員およびオブザーバー 委員長 戸田 保幸(大阪大学大学院) 委員 川村 隆文(東京大学) 委員 甲斐 寿(横浜国立大学大学院) 委員 藪下 和樹(防衛大学校) 委員 勝井 辰博(神戸大学) 委員 土岐 直二(愛媛大学) 委員 日夏 宗彦(海上技術安全研究所) 委員 川島 英幹(海上技術安全研究所) 委員 木村 校優(三井造船昭島研究所) 委員 村上 恭ニ(住友重機械マリンエンジニアリング) 委員 長屋 茂樹(IHI技術研究所) 委員 川北 千春(三菱重工業) 委員(事務局) 田中 寿夫(ユニバーサル造船) 委員代理 池田 剛大(三井造船昭島研究所) オブザーバー 山盛 直樹(日本ペイントマリン) オブザーバー 肥後 清彰(日本ペイントマリン) オブザーバー 高井 章(日本ペイントマリン) オブザーバー 柳田 徹郎(MTI) オブザーバー 安藤 英幸(MTI) 2 次ページ以降は各委員による発表をまとめたものである。配布資料として配布されたもの、 発表用パワーポイントファイルを印刷したもの、発表資料から少し文章をつけたものなど さまざまな形があるが、再度形式をそろえて書き直す時間も考えてそのままの形で収録す ることとした。それぞれの委員ごとにまとめている。内容も計測法について過去の研究を レビューしたもの、過去に委員の機関が行ったものなどさまざまである。また ITTC 委員会 対応の委員会であったので、ブラジルで 2011 年 9 月に開催された総会でのレポートと関連 のグループディスカッションでの発表も資料をいただき収録している。簡単な目次は以下 のとおりである。 川村委員 4 川村「実船スケールレイノルズ数の CFD について」 5 川村、柳田「プロペラ性能に対する表面粗さの影響の CFD による推定」 17 田中委員 25 田中「粗度高さ定義比較」 26 田中「管内流を利用した摩擦抵抗の計測」 27 田中「回転円筒を用いた摩擦抵抗の計測」 32 勝井委員 46 勝井「粗度影響を考慮した平板摩擦抵抗の算定について」 47 勝井,泉「等価砂粗度による平板摩擦抵抗係数の増加量-計算結果の表示について」 52 勝井「後流関数を考慮した平板摩擦の粗度影響について」 54 日夏、川島委員 57 NMRI 流体設計系「平行平板曳航法による平板の摩擦抵抗評価」 58 日夏、川島「摩擦応力計測法について」 72 戸田委員 87 資料1 Hoang, Toda, Sanada ISOPE2009 論文 資料 2 Yamamori, Toda, Yano 資料 3 戸田、眞田、植原 88 ISME2009 論文 94 摩擦抵抗低減に関する考察 100 資料 4 塗膜模型船を用いた水槽実験 111 資料 5 深江丸の推力、トルク計測 118 資料 6 ITTC 表面処理委員会レポート 121 資料7 ITTC グループ討議 Green Ship Atlar 教授資料 資料 8 山盛氏による防汚塗料についての解説資料 3 152 157 川村委員の発表資料 川村「実船スケールレイノルズ数の CFD について」では高レイノルズ数まで CFD コード で計算した例をもとに様々な説明がなされた。 川村、柳田「プロペラ性能に対する表面粗さの影響の CFD による推定」では表面粗度の影 響を考慮した CFD 計算を行い、性能の変化を示して ITTC1978 の式との比較を行った例が 説明された。 4 ᐇ⯪䝇䜿䞊䝹䝺䜲䝜䝹䝈ᩘ䛾 CFD䛻䛴䛔䛶 䠄ᰴ䠅ᩘ್ὶయຊᏛ䝁䞁䝃䝹䝔䜱䞁䜾 ᕝᮧ㝯ᩥ ⫼ᬒ • ≀⌮ⓗ䛺ไ⣙䛜䛒䜛ᶍᆺᐇ㦂䛷䛿䚸ᚲ䛪䝺䜲䝜䝹䝈 ᩘ䛾ᙳ㡪䜢ཷ䛡䜛䛯䜑䚸ᐇ⯪㤿ຊ䛾᥎ᐃ䛻䛚䛔䛶 䛿⤒㦂ⓗ䛺ಟṇ䛜ᚲせ䛷䛒䜛䚹 • ⤒㦂ⓗ䛺ಟṇ䛿㐣ཤ䛾䝕䞊䝍䛻ᇶ䛵䛔䛶⾜䜟䜜䜛 䛯䜑䚸⯪ᆺ䜔せ┠䛜㐣ཤ䛾䝕䞊䝍䛛䜙እ䜜䛶䛔 䜛ሙྜ䛿ಙ㢗ᛶ䛜༑ศ䛷䛺䛔䛸䛔䛖ၥ㢟䛜䛒䜛䚹 • ୍᪉䚸䠟䠢䠠䛻䛚䛔䛶䛿ᐇ⯪䝇䜿䞊䝹䛾ィ⟬䛜ཎ⌮ ⓗ䛻䛿ྍ⬟䛷䛒䜛䛯䜑䚸ィ⟬䛾ಙ㢗ᛶ䜢㧗䜑䜛䛣䛸 䛷䚸ᐇ⯪㤿ຊ䛾᥎ᐃ⢭ᗘ䜢ྥୖ䛥䛫䜛䛣䛸䛜ฟ᮶䜛 䛾䛷䛿䛺䛔䛰䜝䛖䛛䚹 5 ෆᐜ • 㐣ཤ䛾ᐇ⯪䝇䜿䞊䝹䝺䜲䝜䝹䝈ᩘ䛾ィ⟬䛾䝺䝡䝳䞊 1. Y. Tahara, T. Katsui, Y. Himeno: Computation of Ship Viscous Flow at Full Scale Reynolds Number, Journal of The society of Naval Architects of Japan,Vol.192,2002,pp.89-101 2. ᮧୖ䚸ᕝᮧ䚸᭷䠖ᩘ್䝅䝭䝳䝺䞊䝅䝵䞁䛻䜘䜛㧗ᥭຊ⯦䛾ᑻᗘᙳ 㡪䛾ホ౯䚸᪥ᮏ⯪⯧ᾏὒᕤᏛㅮ₇ㄽᩥ㞟 (4), 305-308, 2007 3. ᕝᮧ䚸᳃䠖䝥䝻䝨䝷༢⊂ᛶ⬟䛻ᑐ䛩䜛䝺䜲䝜䝹䝈ᩘ䛾ᙳ㡪䚸᪥ᮏ ⯪⯧ᾏὒᕤᏛㄽᩥ㞟(10), 29-36, 2009 4. 㯤䚸ᒣཱྀ䚸ᕝᮧ䚸᳃䠖 ᐇ⯪䝇䜿䞊䝹䛻䛚䛡䜛⯪యᢠ䛾ᩘ್ண 䚸ᖹᡂ22ᖺᗘ᪥ᮏ⯪⯧ᾏὒᕤᏛᮾ㒊ᨭ㒊⛅Ꮨㅮ₇ㅮ₇ㄽ ᩥ㞟䚸2010 • ⪃ᐹ䛸ㄢ㢟 ὀ┠Ⅼ • ᐇ⯪䝇䜿䞊䝹䝺䜲䝜䝹䝈ᩘ䛻䛚䛡䜛ᦶ᧿ᢠ ಀᩘ • 䛂⾲㠃⢒䛥䛃䛾ᙳ㡪䛾ᙳ㡪 • ᙧ≧ᙳ㡪ಀᩘ䠄⢓ᛶᅽຊᢠ䠅䛻ᑐ䛩䜛䝺䜲 䝜䝹䝈ᩘᙳ㡪 6 Y. Tahara, T. Katsui, Y. Himeno (1) • 2-Layer k-H䝰䝕䝹䛸Wall-function k-H䝰䝕䝹䛻䜘䜛 ᐇ⯪䝺䜲䝜䝹䝈ᩘ䛾ᖹᯈ䛸Series 60࿘䜚ὶ䜜䛾ィ ⟬⤖ᯝ 2-Layer Wall function 䜙䛛䛺ᖹᯈ≧䛾ὶ㏿ศᕸ Y. Tahara, T. Katsui, Y. Himeno (2) 䜙䛛䛺ᖹᯈ䛾ᦶ᧿ᢠಀᩘ 7 Y. Tahara, T. Katsui, Y. Himeno (3) • ⢒䛥䛾ᙳ㡪䛻䛴䛔䛶䠄ᖹᯈ䠅 Y. Tahara, T. Katsui, Y. Himeno (4) Series 60࿘䜚ὶ䜜䠄Wall-Function k-H䠅 • 1+K䛾್(Schoenherr䝧䞊䝇) – ᶍᆺᐇ㦂 – ᶍᆺReィ⟬ – ᐇ⯪Reィ⟬ ᐇ⯪Re䛻䛚䛡䜛కὶศᕸ 1.18 ? 1.20 • ᦶ᧿ᢠಀᩘ䛜ᖹᯈ䛾ሙྜ 䛸ྠ䛨䛸䛩䜛䛸1+K䛻䛿ᐇ㉁ⓗ 䛻䝺䜲䝜䝹䝈ᩘᙳ㡪䛿↓䛔䛸 ᛮ䜟䜜䜛䚹 8 ᮧୖ䚸ᕝᮧ䚸᭷ (1) • ప䝺䜲䝜䝹䝈ᩘᆺSST-k-Z䝰䝕䝹䛻䜘䜚䝅䝸 䞁䜾䝷䝎䞊䛸ᬑ㏻⯦䠄NACA0017䠅䛾ᢠಀ ᩘ䛾䝺䜲䝜䝹䝈ᩘ౫Ꮡᛶ䜢ホ౯ ¾ 䝧䜽䝒䜲䞁A ¾ ᬑ㏻⯦ (NACA0017) ¾ 䝧䜽䝒䜲䞁B ¾ ⯦C-1 ¾ ⯦C-2 ᮧୖ䚸ᕝᮧ䚸᭷ (2) 㻜㻚㻜㻤 㻝㻚㻡 㻟㻰ィ⟬ ᐇ㦂㻔ᅇὶỈᵴ㻕㻭 㻝 㻞㻰ィ⟬ 㻟㻰ィ⟬ ᐇ㦂䠄ᅇὶỈᵴ䠅㻭 ᐇ㦂䠄ᅇὶỈᵴ䠅㻮 㻜㻚㻜㻣 㻜㻚㻜㻢 㻜㻚㻜㻡 㻯㻸 㻯㻰 㻜㻚㻡 㻜㻚㻜㻠 㻜㻚㻜㻟 㻜 㻜㻚㻜㻞 㻙㻜㻚㻡 㻜㻚㻜㻝 㻙㻝 㻙㻣㻡 㻙㻡㻜 㻙㻞㻡 㻜 䃐㼇㼐㼑㼓㼉 㻞㻡 㻡㻜 㻜 㻝㻚㻜㻜㻱㻗㻜㻠 㻣㻡 㻝㻚㻜㻜㻱㻗㻜㻡 㻝㻚㻜㻜㻱㻗㻜㻢 㻾㼑 CD 䛸Reᩘ䛾㛵ಀ CL 䛸㏄ゅ䛾㛵ಀ 9 㻝㻚㻜㻜㻱㻗㻜㻣 ᮧୖ䚸ᕝᮧ䚸᭷ (3) 㻢 㻭 㻮 㻯㻙㻝 㻯㻙㻞 㻺㻭㻯㻭㻜㻜㻝㻣 㻡 㻝㻗㻷 㻠 䝅䝸䞁䜾䝷䝎䞊 㻟 㻞 NACA 㻝 㻜 㻝㻚㻜㻜㻱㻗㻜㻠 㻝㻚㻜㻜㻱㻗㻜㻡 㻝㻚㻜㻜㻱㻗㻜㻢 㻝㻚㻜㻜㻱㻗㻜㻣 㻝㻚㻜㻜㻱㻗㻜㻤 㻾㼑 ᮧୖ䚸ᕝᮧ䚸᭷ (4) 㻜㻚㻜㻤 䝧䜽䝒䜲䞁A -2 [deg] 㻯㼐䠖ᢠಀᩘ C D 䠖ᢠಀᩘ C 㻯㼐㼜䠖ᅽຊᢠಀᩘ DP 䠖ᅽຊᢠಀᩘ 㻜㻚㻜㻣 㻜㻚㻜㻢 C 㻯㼒䠖ᦶ᧿ᢠಀᩘ f 䠖ᦶ᧿ᢠಀᩘ 2Cf 㻯㼒㻜䠖ᖹᯈᦶ᧿ᢠಀᩘ 0䠖ᖹᯈᦶ᧿ᢠಀᩘ 㻜㻚㻜㻡 㻜㻚㻜㻠 㻜㻚㻜㻟 㻜㻚㻜㻞 㻜㻚㻜㻝 㻜 㻝㻚㻜㻜㻱㻗㻜㻠 㻝㻚㻜㻜㻱㻗㻜㻡 㻝㻚㻜㻜㻱㻗㻜㻢 㻾㼑 10 㻝㻚㻜㻜㻱㻗㻜㻣 㻝㻚㻜㻜㻱㻗㻜㻤 ᮧୖ䚸ᕝᮧ䚸᭷ (5) 㻜㻚㻜㻢 㻯㼐㼜䠖ᅽຊᢠಀᩘ 㻯㼐㼎㼜䠖䝧䞊䝇㒊ศ 㻯㼐㼜㻙㻯㼐㼎㼜䠖䝧䞊䝇㒊ศ௨እ 㻯㼒㻜䠖ᖹᯈᦶ᧿ᢠಀᩘ 㻜㻚㻜㻡 㻜㻚㻜㻠 㻜㻚㻜㻟 䝧䞊䝇㒊ศ 㻜㻚㻜㻞 㻜㻚㻜㻝 䝧䞊䝇㒊ศ௨እ䛾ᅽຊᢠ䛿 㧗䛔Reᩘ䛷Cf0䛻ẚ䠛 㻜 㻝㻚㻜㻜㻱㻗㻜㻠 㻝㻚㻜㻜㻱㻗㻜㻡 㻝㻚㻜㻜㻱㻗㻜㻢 㻝㻚㻜㻜㻱㻗㻜㻣 㻝㻚㻜㻜㻱㻗㻜㻤 㻾㼑 ᕝᮧ䚸᳃ (1) • ప䝺䜲䝜䝹䝈ᩘᆺSST-k-Z䝰䝕䝹䛻䜘䜚䝥䝻䝨䝷䛾 ༢⊂ᛶ⬟䛾䝺䜲䝜䝹䝈ᩘ౫Ꮡᛶ䜢ホ౯ 0.8 Exp. Cal. k-ω Cal. k-ω-trans 0.7 ηO KT, 10KQ, ηO 0.6 0.5 0.4 10KQ 0.3 0.2 KT 0.1 0 0.1 㟷㞼CP 0.2 0.3 0.4 0.5 0.6 J Rn( K ) 3.23 u 105 11 0.7 0.8 0.9 1 D=0.25mᶍᆺ䝇䜿䞊䝹 ᕝᮧ䚸᳃ (2) 1.2 Exp. Cal. k-ω Cal. k-ω-trans KT, 10KQ, ηO 1 0.8 ηO ᐇ㦂 㒊ศὶィ⟬ 0.6 㠃ὶィ⟬ 10KQ 0.4 0.2 KT 0 0.2 0.4 0.6 0.8 1 1.2 J MP282 Rn( K ) 3.5 u105 D=0.25mᶍᆺ䝇䜿䞊䝹 ᕝᮧ䚸᳃ (3) 䝺䜲䝜䝹䝈ᩘᙳ㡪䛻䛴䛔䛶䛾⪃ᐹ KT KTf 'KT ↓㝈䝺䜲䝜䝹䝈ᩘ䛷䛾್ 'KT KQ ᭷㝈䝺䜲䝜䝹䝈ᩘᙳ㡪 'KTP KTV ᅽຊᡂศ䛾ኚ K Qf 'K Q 'K Q 'K QP K QV ᦶ᧿ᡂศ䛾ኚ䠙ᦶ᧿ᡂศ 12 ᕝᮧ䚸᳃ (4) 0.004 ΔKTV 0.002 0.002 Seiunmaru CP J=0.6 Seiunmaru CP J=0.4 MP282 J=1.1 ΔKQP, ΔKQV -0.002 -0.004 ΔKTP 0.0005 0 -0.0005 ΔKQP -0.001 -0.008 -0.0015 -0.01 100000 1e+06 1e+07 1e+08 -0.002 100000 1e+06 1e+07 1e+08 Rn(K) Rn(K) ᕝᮧ䚸᳃ (5) 0.025 Seiunmaru CP J=0.6 Seiunmaru CP J=0.4 MP282 J=1.1 0.02 ⣙3% 10ΔKQ 0.015 0.01 ΔKT, 10ΔKQ ΔKTP, ΔKTV ΔKQV 0.001 0 -0.006 Seiunmaru CP J=0.6 Seiunmaru CP J=0.4 MP282 J=1.1 0.0015 4Cf0 0.005 0 -2.5Cf0 -0.005 ΔKT -0.01 ⣙4% -0.015 -0.02 0 0.001 0.002 0.003 Cf0 0.004 0.005 0.006 Kempf䛾䝺䜲䝜䝹䝈ᩘ䛻䛚䛡䜛ᖹᯈᦶ᧿ᢠಀᩘ 13 㯤䚸ᒣཱྀ䚸ᕝᮧ䚸᳃(1) • SST-k-Z䝰䝕䝹䛻䜘䜛䝍䞁䜹䞊⯪ᆺ࿘䜚䛾ィ⟬ • Re=1e7䡚ᐇ⯪䝇䜿䞊䝹 㻜㻚㻜㻜㻠㻜 㻯㼢㼜㼋㼏㼍㼘 㻯㼒㼋㼏㼍㼘 㻜㻚㻜㻜㻟㻡 㻯㼠㼋㼏㼍㼘 㻯㼒㻜 㻜㻚㻜㻜㻟㻜 㻜㻚㻜㻜㻞㻡 㻜㻚㻜㻜㻞㻜 㻜㻚㻜㻜㻝㻡 㻜㻚㻜㻜㻝㻜 㻜㻚㻜㻜㻜㻡 㻜㻚㻜㻜㻜㻜 㻝㻚㻜㻱㻗㻜㻢 㻝㻚㻜㻱㻗㻜㻣 㻝㻚㻜㻱㻗㻜㻤 㻝㻚㻜㻱㻗㻜㻥 㻝㻚㻜㻱㻗㻝㻜 㻾㼑㼥㼚㼛㼘㼐㼟㻌㼚㼡㼙㼎㼑㼞 㯤䚸ᒣཱྀ䚸ᕝᮧ䚸᳃(2) 㻲㼛㼞㼙㻌㼒㼍㼏㼠㼛㼞 K_cal / K_exp 㻝㻚㻢㻜 㻝㻚㻠㻜 㻝㻚㻞㻜 㻷㻛㻷㼋㼑㼤㼜 㻷㻓㻛㻷㼋㼑㼤㼜 㻷㻓㻓㻛㻷㼋㼑㼤㼜 㻝㻚㻜㻜 㻜㻚㻤㻜 㻝㻚㻜㻱㻗㻜㻢 㻝㻚㻜㻱㻗㻜㻣 㻝㻚㻜㻱㻗㻜㻤 㻝㻚㻜㻱㻗㻜㻥 㻾㼑㼥㼚㼛㼘㼐㼟㻌㼚㼡㼙㼎㼑㼞 14 㻝㻚㻜㻱㻗㻝㻜 㻯㼠㻌㻌㼣㻛㼛㻌㻯㼣 㯤䚸ᒣཱྀ䚸ᕝᮧ䚸᳃(3) 㻜㻚㻜㻜㻞㻡 㻔㻝㻗㻷㼋㼑㼤㼜㻕㻖㻯㼒㼟㻗䂴㻯㼒 㻜㻚㻜㻜㻞㻠 㻯㼢㼜㼋㼏㼍㼘㻗㻯㼒㼋㼏㼍㼘 㻜㻚㻜㻜㻞㻟 㻜㻚㻜㻜㻞㻞 㻜㻚㻜㻜㻞㻝 㻜㻚㻜㻜㻞㻜 㻜㻚㻜㻜㻝㻥 㻜㻚㻜㻜㻝㻤 㻤 㻤㻚㻡 㻥 㻥㻚㻡 㻝㻜 㻸㼛㼓㻔㻾㼑㻕 ⪃ᐹ • Cf䛾ィ⟬್䛿䝰䝕䝹䛾ಀᩘ䛻౫Ꮡ䛩䜛䛯䜑䚸 ィ⟬䛛䜙᪂䛯䛺▱ぢ䜢⏕䜏ฟ䛩䛣䛸䛿ᅔ㞴䛷 䛒䜛䚹 • ⩼ᆺ䛾䜘䛖䛺䛺ὶ⥺ᆺ䛾ሙྜ䛿1+K䛿 Cf䛻ẚ䛩䜛䛜䚸䛺ὶ⥺ᆺ䛷䛺䛔ሙྜ 䛿䚸㧗䝺䜲䝜䝹䝈ᩘ䛻䛚䛔䛶್䛜ቑຍ䛩䜛䚹 • ᐇ⯪㤿ຊ᥎ᐃ䛻䛚䛡䜛'Cf䛻䛿⢒䛥䛾ᙳ㡪䛸 1+K䛾ቑຍ䛾ᙳ㡪䛜ྵ䜎䜜䜛䚹 • 1-t䛻ᑐ䛩䜛䝺䜲䝜䝹䝈ᩘᙳ㡪䛿䛒䜛䛾䛛䠛 • Cw䛻ᑐ䛩䜛䝺䜲䝜䝹䝈ᩘᙳ㡪䛿䛒䜛䛾䛛䠛 15 ᐇ⯪䝇䜿䞊䝹CFD䛾ㄢ㢟(1) • k-w䝰䝕䝹䛾ḞⅬ Cf䛾᮰䛜ᝏ䛔䠄y+䜢㠀ᖖ䛻ᑠ䛥䛟䛩䜛ᚲせ䛜䛒䜛䠅 㻝㻚㻞 㻯㼒㻛㻯㼒䛾᮰್ 㻝㻚㻝㻡 㻝㻚㻝 㻝㻚㻜㻡 㻲㼘㼡㼑㼚㼠 㻻㼜㼑㼚㻲㻻㻭㻹 㻝 㻜㻚㻥㻡 㻜㻚㻥 㻜㻚㻤㻡 㻜㻚㻤 㻜㻚㻜㻝㻜 㻜㻚㻝㻜㻜 㻝㻚㻜㻜㻜 㼥㻗 㻝㻜㻚㻜㻜㻜 㻝㻜㻜㻚㻜㻜㻜 ᐇ⯪䝇䜿䞊䝹CFD䛾ㄢ㢟(2) • 䝯䝑䝅䝳䛾ၥ㢟 Re=1e9䛸䛩䜛䛸Cf0=0.0015 Lpp=1䛸䛩䜛䛸y+=0.1䛸䛩䜛䛻䛿'y=3.6e-9 ಸ⢭ᗘ䛷䜒䝯䝖䝸䝑䜽䛾ィ⟬䛷᱆ⴠ䛱䛜Ẽ䛻䛺䜛 䠄୍㒊䛾䝋䝣䝖䛷䛿䝯䝑䝅䝳సᡂ䛛䝯䝖䝸䝑䜽䛾ィ⟬䛷䜶 䝷䞊䛻䛺䜛䠅 • ᙧ≧ฎ⌮䛾ၥ㢟 ⯦䛾᭷↓䜔䚸䝅䝱䝣䝖䚸䝪䝇䛾ฎ⌮䛻1+K䛜౫Ꮡ䛩䜛䚹 16 䝥䝻䝨䝷ᛶ⬟䛻ᑐ䛩䜛⾲㠃⢒䛥䛾ᙳ㡪䛾 䠟䠢䠠䛻䜘䜛᥎ᐃ 䠄ᰴ䠅ᩘ್ὶయຊᏛ䝁䞁䝃䝹䝔䜱䞁䜾 ᕝᮧ㝯ᩥ 䠄ᰴ䠅MTI ᰗ⏣ᚭ㑻 ┠ⓗ • ⯪⯧䛾᥎㐍ᛶ⬟䛿䚸⯪య䛸䝥䝻䝨䝷䛾ởᦆ䛻䜘䜚పୗ䛩䜛䚹 • ᭱㐺䛺䝯䞁䝔䝘䞁䝇䛾䛯䜑䛻䛿䚸⯪య䛾ởᦆ䛸䝥䝻䝨䝷䛻䜘 䜛ởᦆ䛾ᙳ㡪䜢⢭ᐦ䛻ண ཬ䜃ホ౯䛩䜛䛣䛸䛜㔜せ䛷䛒䜛䚹 • ㏻ᖖ䛿㏿ຊ䛸ᅇ㌿ᩘ䛸䝖䝹䜽䛾䜏䛜ィ 䛥䜜䛶䛔䜛䛜䚸䛣䜜 䛻ຍ䛘䛶᥎ຊ䛾ィ 䜢⾜䛖䛣䛸䛻䜘䜚䚸⯪య䛸䝥䝻䝨䝷䛾ở ᦆ䛾ᙳ㡪䜢ศ㞳䛩䜛䛣䛸䛜ฟ᮶䜛䚹 • ୍᪉䚸䝥䝻䝨䝷䛾䝖䝹䜽䛾ኚ䛸᥎ຊ䛾ኚ䛾㛵ಀ䛜ศ䛛䛳 䛶䛔䜜䜀䚸ィ 䛧䛯䝖䝹䜽䛛䜙᥎ຊ䛾ኚ䜢᥎ᐃ䛷䛝䜛䚹 • 䛥䜙䛻䚸ୖ䛾୧᪉⾜䛖䛣䛸䛻䜘䜚┦䛻᳨ド䛜ྍ⬟䛸䛺䜚䚸⢭ ᗘ䛾ྥୖ䛜ᮇᚅ䛷䛝䜛䚹 • ᮏ◊✲䛷䛿䚸CFD䛻䜘䜚䝥䝻䝨䝷䛾䝖䝹䜽䛸᥎ຊ䛾ኚ䛾ண 䜢⾜䛖䚹 17 ඛ⾜◊✲ • Wan et al., The Experiment and Numerical Calculation of Propeller Performance with Surface Roughness Effects, 㛵す㐀⯪༠ㄽᩥ㞟 (238), 49-54, 2002 • ☐⋢䜙䚸ᐇᾏᇦ⯟⾜୰⯪⯧䛾᥎㐍ᛶ⬟ศᯒἲ䛻㛵䛩䜛 ◊✲ : ⯪⯧䝥䝻䝨䝷⾲㠃⢒ᗘᙳ㡪䛾ホ౯䚸㛵す㐀⯪༠ㄽ ᩥ㞟 (239), 55-60, 2003 – ⢒ᗘ䜢䛡䛯䝥䝻䝨䝷ᶍᆺ䛾ᐇ㦂 – ቃ⏺ᒙ⌮ㄽ䛻䜘䜛ᩘ್ィ⟬ – ⚄ᡞၟ⯪䛾⦎⩦⯪䛂῝Ụ䛃䛾ᐇ⯪ィ • ᕝᮧ 㝯ᩥ䚸᳃ ᣅஓ䚸䝥䝻䝨䝷༢⊂ᛶ⬟䛻ᑐ䛩䜛䝺䜲䝜䝹 䝈ᩘ䛾ᙳ㡪䚸᪥ᮏ⯪⯧ᾏὒᕤᏛㄽᩥ㞟(10), 29-36, 2009 – ᦶ᧿ᢠಀᩘ䛾ኚ䠄䝺䜲䝜䝹䝈ᩘ䛻䜘䜛䠅䛻䜘䜛䝥䝻䝨䝷༢⊂ᛶ⬟ 䛾ኚ䛾CFD䛻䜘䜛ண ᐇෆᐜ • 䛒䜛䝁䞁䝔䝘⯪䛾䝥䝻䝨䝷䜢䛻䚸⾲㠃⢒ᗘ䜢ኚ 䛥䛫䛶䝥䝻䝨䝷༢⊂ᛶ⬟䛾ண ィ⟬䜢ᐇ⯪䝺䜲䝜䝹 䝈ᩘ䛷⾜䛖䚹 • 䝥䝻䝨䝷ᛶ⬟䛾ィ⟬䛿Fluent䜢⏝䛔䛶䚸㐣ཤ䛾◊✲ 䛸ྠᵝ䛾᪉ἲ䛷⾜䛖䚹 • ⾲㠃⢒ᗘ䛾ᙳ㡪䛿k-w-SST䝰䝕䝹䛾⢒ᗘ䝰䝕䝹䛻 䜘䜚⾜䛖䚹 • 䠄ᐇ⯪䝕䞊䝍䛸䛾ẚ㍑᳨ド䜢⾜䛖䠅 18 ᑐ㇟䝥䝻䝨䝷 せ┠ 㻰 㼆 㻼㻛㻰㻌㼍㼠㻌㻜㻚㻣㻾 㼏㻌㼍㼠㻌㻜㻚㻣㻾 㻱㻭㻾 㻿㼑㼏㼠㼕㼛㼚 㻮㼛㼟㼟㻌㻾㼍㼠㼕㼛 ⣙㻥 㻢 ⣙㻝 ⣙㻟 ⣙㻜㻚㻥 㻺㻭㻯㻭 㻜㻚㻝㻥㻜 㼙 㼙 POT䛸䛾ẚ㍑ 1 CFD Exp. 0.9 10KQ 0.8 ηo KT, 10KQ, ηo 0.7 KT 0.6 0.5 0.4 0.3 0.2 0.1 0 0 0.2 0.4 0.6 J 0.8 1 㠃䜢ᐃ䛧䛯ィ⟬䠄Rn(K)=2.9e5䠅 䝥䝻䝨䝷䜸䝣䝉䝑䝖䛜䛺䛟䚸ᙧ≧䛿୍㒊᥎ᐃ 19 1.2 ᖹᯈ䛾⢒ᗘ䛸ᦶ᧿ᢠಀᩘ䛾㛵ಀ • ᖹᯈ䛾㛗䛥䛿⣙3m 䠄0.7R䛾䝁䞊䝗㛗䠅 • 䝺䜲䝜䝹䝈ᩘ䛿ᐇ⯪䛾Kempf䛾䝺䜲䝜䝹䝈ᩘ Re ⢒㠃ᖹᯈ䛾ᦶ᧿ᢠಀᩘ䛾ィ⟬್ ks 㼗㼟㻌㻔P㼙㻕 㼗㼟㻛㻯㻜㻚㻣㻾 㼗㼟㻗 㻯㼒 㻜㻚㻜 㻜㻚㻜㻜㻱㻗㻜㻜 㻜㻚㻜 㻞㻚㻜㻢㻱㻙㻜㻟 㻟㻚㻝 㻝㻚㻜㻜㻱㻙㻜㻢 㻟㻚㻝 㻞㻚㻜㻣㻱㻙㻜㻟 㻢㻚㻟 㻞㻚㻜㻜㻱㻙㻜㻢 㻢㻚㻞 㻞㻚㻞㻜㻱㻙㻜㻟 㻝㻡㻚㻣 㻡㻚㻜㻜㻱㻙㻜㻢 㻝㻡㻚㻢 㻞㻚㻡㻢㻱㻙㻜㻟 㻟㻝㻚㻠 㻝㻚㻜㻜㻱㻙㻜㻡 㻟㻝㻚㻞 㻞㻚㻥㻤㻱㻙㻜㻟 㻢㻞㻚㻤 㻞㻚㻜㻜㻱㻙㻜㻡 㻢㻞㻚㻠 㻟㻚㻠㻟㻱㻙㻜㻟 㻝㻡㻢㻚㻥 㻡㻚㻜㻜㻱㻙㻜㻡 㻝㻡㻡㻚㻥 㻠㻚㻜㻞㻱㻙㻜㻟 䠖➼౯◁⢒ᗘ k s uW Q '㻯㼒 㻜㻚㻜㻜㻱㻗㻜㻜 㻝㻚㻥㻞㻱㻙㻜㻡 㻝㻚㻠㻟㻱㻙㻜㻠 㻡㻚㻜㻠㻱㻙㻜㻠 㻥㻚㻞㻝㻱㻙㻜㻠 㻝㻚㻟㻤㻱㻙㻜㻟 㻝㻚㻥㻢㻱㻙㻜㻟 㻠㻚㻡㻜㻱㻙㻜㻟 㻠㻚㻜㻜㻱㻙㻜㻟 㻟㻚㻡㻜㻱㻙㻜㻟 㻟㻚㻜㻜㻱㻙㻜㻟 㻞㻚㻡㻜㻱㻙㻜㻟 㻯㼒 㻯㼒㻜 㻯㼒 㻞㻚㻜㻜㻱㻙㻜㻟 㻝㻚㻡㻜㻱㻙㻜㻟 㻝㻚㻜㻜㻱㻙㻜㻟 㻡㻚㻜㻜㻱㻙㻜㻠 㻜㻚㻜㻜㻱㻗㻜㻜 㻜㻚㻜 㻞㻜㻚㻜 㻠㻜㻚㻜 㻢㻜㻚㻜 㻤㻜㻚㻜 㻝㻜㻜㻚㻜 㼗㼟㻌㻔䝬䜲䜽䝻䝯䞊䝖䝹㻕 㻝㻞㻜㻚㻜 㻝㻠㻜㻚㻜 㻝㻢㻜㻚㻜 㻝㻤㻜㻚㻜 㻞㻚㻡㻜㻱㻙㻜㻟 㻞㻚㻜㻜㻱㻙㻜㻟 㻝㻚㻡㻜㻱㻙㻜㻟 㻰㼑㼘㼠㼍㻌㻯㼒 ks 9.66 u 10 7 㻰㼑㼘㼠㼍㻌㻯㼒 㼥㻩㻜㻚㻜㻜㻝㻠㻣㻌㼤㻌㻙㻌㻜㻚㻜㻜㻝㻞㻡 㻝㻚㻜㻜㻱㻙㻜㻟 㻡㻚㻜㻜㻱㻙㻜㻠 㻜㻚㻜㻜㻱㻗㻜㻜 㻝㻚㻜 㻝㻜㻚㻜 㻝㻜㻜㻚㻜 㼗㼟㻌㻔䝬䜲䜽䝻䝯䞊䝖䝹㻕 20 㻝㻜㻜㻜㻚㻜 ⢒䛥䛾䛒䜛ᐇ⯪䝥䝻䝨䝷䛾ィ⟬ ks 0, 5, 10, 20, 50, 100, 200Pm 1 CFD Smooth CFD ks=200μm Est. Full 0.9 10KQ 0.8 ηo KT 0.6 0.5 0.4 0.3 0.2 0.1 0 0 0.2 0.4 0.6 J 0.8 1 1.2 㻜㻚㻞㻡㻤 㻜㻚㻞㻡㻢 㻜㻚㻞㻡㻠 㻜㻚㻞㻡㻞 㻷㼀 㻜㻚㻞㻡 㻜㻚㻞㻠㻤 㻜㻚㻞㻠㻢 㻜㻚㻞㻠㻠 㻜㻚㻞㻠㻞 㻜㻚㻞㻠 㻜 㻡㻜 㻝㻜㻜 㻝㻡㻜 㼗㼟㻌㻔䝬䜲䜽䝻䝯䞊䝖䝹㻕 㻞㻜㻜 㻞㻡㻜 㻜 㻡㻜 㻝㻜㻜 㻝㻡㻜 㼗㼟㻌㻔䝬䜲䜽䝻䝯䞊䝖䝹㻕 㻞㻜㻜 㻞㻡㻜 㻜㻚㻜㻠㻡㻤 㻜㻚㻜㻠㻡㻢 㻜㻚㻜㻠㻡㻠 㻜㻚㻜㻠㻡㻞 㻷㻽 KT, 10KQ, ηo 0.7 㻜㻚㻜㻠㻡 㻜㻚㻜㻠㻠㻤 㻜㻚㻜㻠㻠㻢 㻜㻚㻜㻠㻠㻠 㻜㻚㻜㻠㻠㻞 タィⅬ (J=0.7)䛻䛚䛡䜛➼౯◁⢒ᗘ䛸KT䛸KQ䛾㛵ಀ 21 㻜 㻜 㻜㻚㻜㻜㻜㻡 㻜㻚㻜㻜㻝 㻜㻚㻜㻜㻝㻡 㻜㻚㻜㻜㻞 㻜㻚㻜㻜㻞㻡 㻙㻜㻚㻜㻜㻞 㻙㻜㻚㻜㻜㻠 㻰㼑㼘㼠㼍㻌㻷㼀 㻙㻜㻚㻜㻜㻢 㻙㻜㻚㻜㻜㻤 㻙㻜㻚㻜㻝 㼥㻌㻩㻌㻙㻢㻚㻡㻞㻤㻣㼤 㻙㻜㻚㻜㻝㻞 㻙㻜㻚㻜㻝㻠 㻙㻜㻚㻜㻝㻢 㻰㼑㼘㼠㼍㻌㻯㼒 㻜㻚㻜㻜㻝㻠 㻜㻚㻜㻜㻝㻞 㻜㻚㻜㻜㻝 㻰㼑㼘㼠㼍㻌㻷㻽 㼥㻌㻩㻌㻜㻚㻡㻤㻝㻟㼤 㻜㻚㻜㻜㻜㻤 㻜㻚㻜㻜㻜㻢 㻜㻚㻜㻜㻜㻠 㻜㻚㻜㻜㻜㻞 㻜 㻜 㻜㻚㻜㻜㻜㻡 㻜㻚㻜㻜㻝 㻜㻚㻜㻜㻝㻡 㻜㻚㻜㻜㻞 㻜㻚㻜㻜㻞㻡 㻰㼑㼘㼠㼍㻌㻯㼒 ᦶ᧿ᢠቑຍ'Cf䛸'KT, 'KQ䛾㛵ಀ ITTC1978䛸䛾ẚ㍑ ITTC1978䛷䛿䚸䝥䝻䝨䝷䛾ᑻᗘᙳ㡪䛻䛴䛔䛶௨ୗ䛾ᘧ䛜♧䛥䜜䛶䛔䜛䚹 C P 'K T 0.3Z 'C D DD 'K Q 0.25Z C 'C D D ୖ䛛䜙'CD䜢ᾘཤ䛧䚸䝢䝑䝏ẚ1.05䜢௦ධ䛩䜛䛸 'K T 1.26'K Q ୍᪉䚸ᅇ䛾ィ⟬⤖ᯝ䛛䜙䛿 ' K T 6 .5 ' C f 'K Q 0.58'C f 'K T 11.2'K Q ITTC1978䛾ᘧ䛿᥎ຊ䛾ኚ䜢㐣ᑠホ౯䛩䜛䚹 䠄䛣䛾䛣䛸䛿䜙䜒ᣦ䛧䛶䛔䜛䠅 22 ITTC1978䛸䛾ẚ㍑䠄⥆䛝䠅 ITTC1978䛾ᘧ䛾ᐃᩘ㒊ศ䛰䛡䜢ᅇ䛾ィ⟬⤖ᯝ䛷⨨䛝䛘䜛䛸௨ୗ 䛾䜘䛖䛻䛺䜛䚹 'K T 2.96 Z 'K Q 0.28Z C P 'C f DD C 'C f D 'K T 0.3Z C P 'C D DD 'K Q 0.25Z C 'C D D ITTC1978 䛺䛚䚸ITTC1978䛾'CD䛿᩿㠃䛾ᢠಀᩘ䛺䛾䛷䚸 'C D | 2 ' C f 䛷䛒䜛䚹 䚸すᕝ䜙䛻䜘䜛ᐇ⯪ィ 䛸䛾ẚ㍑ ᅇ䛾CFD䛻ᇶ䛵䛟ಀᩘ 'K T 9 .0 ' K Q ITTC1978䛾ಀᩘ 'K T 23 1.02'K Q 䜎䛸䜑 • ⾲㠃⢒ᗘ䜢⪃៖䛧䛯CFDィ⟬䛻䜘䜚䚸⾲㠃䛾ᦶ᧿ᢠಀᩘ 䛾ቑຍ䛸䝥䝻䝨䝷ᛶ⬟䛾ኚ䛾㛵ಀ䜢ホ౯䛧䛯䚹 • ᦶ᧿ᢠ䛾ቑຍ('Cf)䛸KT䚸KQ䛾ኚ('KT,'KQ)䛿ẚ㛵 ಀ䛻䛒䜛䚹 • ᚑ䛳䛶䚸'KT䛸'KQ䛿ẚ㛵ಀ䛻䛒䜛䚹 • ITTC1978䛾┦㛵ᘧ䛿'KT䜢୍᱆㏆䛟㐣ᑠホ౯䛧䛶䛔䜛ྍ⬟ ᛶ䛜㧗䛔䚹 • 䝺䜲䝜䝹䝈ᩘ䚸⢒ᗘ䛸'Cf䛾㛵ಀཬ䜃䝥䝻䝨䝷せ┠䛸'Cf 䛸 'KT䛸'KQ䛾㛵ಀ䛻䛴䛔䛶ᩚ⌮䛩䜛䛣䛸䛻䜘䜚䚸୍⯡䛥䜜 䛯䝥䝻䝨䝷ᛶ⬟ኚ䛾ண ᘧ䜢స䜛䛣䛸䛜ฟ᮶䜛䛸ᛮ䜟䜜䜛䚹 24 田中委員の発表資料 田中「粗度高さ定義比較」では様々な粗度の定義(計測器も含めて)があるが、同じ粗度 高さであっても、どの定義を使っているか認識することが必要との話がなされた。 田中「管内流を利用した摩擦抵抗の計測」では、これまでのパイプを使った研究がレビュ ーされた。チャンネル流れでの計測との比較もなされた。 田中「回転円筒を用いた摩擦抵抗の計測」ではこれまで田中委員により行われた回転円筒 試験装置による試験が説明された。 25 2010/04/16 粗度高さ定義の比較 ユニバーサル造船 26 田中 管内流を利用した摩擦抵抗の計測 ユニバーサル造船 田中寿夫 1 直線円管を用いた摩擦抵抗計測:概要 • • • • 山崎・小野木・仲渡・姫野・田中・鈴木:「表面粗 度による抵抗増加の研究(第1報告)、日本造 船学会論文集153号、1983 小野木・山崎・仲渡・姫野・田中・鈴木:「表面粗 度による抵抗増加の研究(第1報告)、日本造 船学会論文集155号、1984 直線円管における圧力損失を計測することによ り、円管内面の摩擦抵抗を計測 円管内面の粗度あるいは塗装状態が摩擦抵抗 に及ぼす影響を明らかにすることが目的 27 2 直線円管を用いた摩擦抵抗計測:抵抗の計測方法 • 内径50mm・全長 4,000mmの直線円管を 使用 • 側壁に設けた静圧孔を 用いて管路の圧力損失 を計測し、これをDarcy の摩擦抵抗係数に換算 • 静圧孔から総圧管を挿 入して円管断面内の流 速分布も計測 3 直線円管を用いた摩擦抵抗計測:粗度の計測方法 28 • 円管内側に研磨用砂 を接着して砂粗度を模 擬 • 円管内側の粗度を計 測する代わりに、同様 の方法で作成した粗 度平板について、BS RA式可搬型粗度計で 表面粗度を計測 • BSRA粗度は、タング ステン球を対象面に 接触させ、面に沿って 100mm移動させたとき の最大粗度を示す 4 直線円管を用いた摩擦抵抗計測:管内の速度分布 • 総圧管を断面内でトラ バースさせて、速度分 布を計測 • 管直径の40倍程度の 助走区間をとっている ため、計測部では安 定した速度分布が得 られている 5 直線円管を用いた摩擦抵抗計測:滑面の摩擦抵抗 • 圧力損失から求めた管摩擦抵抗係数fをPrandtlの実験式と比較 • 広範囲のReynolds数にわたって、実験値とよく一致 • ばらつきも少ない 29 6 直線円管を用いた摩擦抵抗計測:粗面の摩擦抵抗 • ほとんどの供試粗面 円管はReynolds数に よらず一定値の摩擦 抵抗となっている→流 体力学的に完全粗面 の状態 • 管摩擦抵抗係数fは Reynilds数に依存せ ず,Nikuradseの砂粗度 ks/Dの関数となってい る 7 直線円管を用いた摩擦抵抗計測:粗度の影響 Pipe No. f Ks/D Ks (μm) KBSRA (μm) Ks/kBSRA 2 0.018 0.0007 36 64 0.49 3 0.028 0.0038 196 130 1.51 4 0.031 0.0054 266 202 1.32 5 0.044 0.0151 778 538 1.45 6 0.059 0.0324 1685 1132 1.46 30 8 直線円管を用いた摩擦抵抗計測:粗度の影響 • 計測された摩擦抵抗 係数から求めた Nikuradseの砂粗度ks と、BSRAの粗度は比 例関係にある • 粗度が小さい場合は、 必ずしも比例にはなら ない • 新造船の場合の粗度 は高々50~150μm 程度であり、比例関係 が当てはまるとは言い 切れない 9 溶接ビードが摩擦抵抗に及ぼす影響 ・「白勢:粗面と溶接ビードによる船の抵抗増加(西部造船会報75 号)」 ・「白勢:粗面と溶接ビードによる船の抵抗増加(西部造船会報75号)」 ・Lpp=225m の船体が10 10ブロックからなると仮定 ブロックからなると仮定 ・Lpp=225mの船体が ・溶接ビードは幅20mm ・高さ5mm 5mmと仮定 と仮定 ・溶接ビードは幅20mm・高さ ・摩擦抵抗に及ぼす影響は2%程度⇒粗度の1/10 オーダー ・摩擦抵抗に及ぼす影響は2%程度⇒粗度の1/10オーダー 5mm 31 10 S7委員会#6 回転円筒を用いた 摩擦抵抗の計測 ユニバーサル造船 田中寿夫 回転円筒試験装置(外観) モーター トルク計 外円筒(固定) 32 回転円筒試験装置(内部) 回転軸 エンドプレート (2次流れを抑制) 供試円筒 (側面を塗装) 実船における摩擦抵抗推定法 1. 回転円筒-固定円筒管に生じる境界層内にお ける速度分布に壁法則を仮定 2. 壁法則から円筒表面に作用する平均摩擦応力 を推定 3. 回転円筒試験で得られた摩擦抵抗係数に一致 するように壁法則で等価砂粗度Keを決定 4. 得られた等価砂粗度によって実船尺度におけ る摩擦抵抗の増減量を評価 33 流速分布の比較 -人工粗度円筒の場合- 1 •境界層内速度分 布に壁法則を仮定 •表面粗度の異なる 円筒の実験値と比 較 •等価砂粗度Keを 仮定して求めた速 度分布は実験結 果と定量的に良好 な一致を示す Estimated (Bout=500m) Ks= 0m Ks= 34m Ks=121m Measured RF1(Rz= 6.2m) RF3(Rz= 16.6m) RF5(Rz=100.5m) 0.9 0.8 0.7 u/U 0.6 0.5 0.4 0.3 0.2 0.1 0 1 1.5 2 2r/D 2.5 3 平均摩擦応力の比較 -人工粗度円筒の場合- 0.0036 0.0035 0.0034 Estimated (Log law×1.96) Ks= 0m Ks= 34m Ks=121m Measured RF1(Rz= 6.2m) RF3(Rz= 16.6m) RF5(Rz=100.5m) 0.0033 0.0032 Ct 0.0031 0.003 0.0029 0.0028 0.0027 0.0026 2 3 4 5 6 7 Rn 8 9 10 34 11 12 +6 [10 ] •流速分布から 決定した等価 砂粗度Keを用 いて供試円筒 に作用する平 均摩擦応力を 推定 •レイノルズ数の 変化が摩擦応 力に及ぼす影 響はよく推定さ れている 塗膜面の表面状態変化を 考慮した摩擦抵抗の計測法 1)供試塗膜を側面に塗装した円筒を作製 2)試験装置で回転数0~700rpmの範囲で回 転トルクを計測→摩擦抵抗係数を算出 3)表面粗度をJIS方式で計測 4)エイジング用池で1ヶ月間連続回転(円筒 表面における回転速度が4.5ノット相 当) 5)2)~4)の過程を3ヶ月間繰り返す エイジング装置 新鮮な海水が常時循環するプール内で供試円筒を連続回転 実船まわり流れにおける塗膜面の暴露状態を模擬 35 供試塗膜の要目 No. 初期粗度 消耗度 接触角 (μm) (μm/年) (°) 性質 RF1 無塗装滑面(基準円筒) 11.9 - - SF1 自己研磨型 32.3 78.0 - SF3 自己研磨型 45.6 41.0 - SF5 自己研磨型 32.5 162.0 - SF5R 自己研磨型 87.3 162.0 - SW1 SF5R 撥水性アクリル系 23.1 - 85 撥水性シリコン系 24.0 - 129 初期粗度:JIS方式で計測した最大値 消耗度:15ノット相当回転速度で研磨した場合の値 エイジングによる生物付着 (撥水性塗膜) エイジング過程でスライム(藻類の死骸)が付着 初期状態 1ヶ月経過 36 自己研磨型塗膜の抵抗係数 (初期状態) 初期粗度大のSF5Rの抵抗が非常に大きい 他の塗膜面は滑面を若干上回る程度 0.0036 0.0035 0.0034 0.0033 0.0032 Ct 0.0031 0.003 0.0029 0.0028 0.0027 00/09/11 RF1 SF1 SF3 SF5 SF5R 0.0026 2 3 4 5 6 7 Rn 8 9 10 11 12 +6 [10 ] 自己研磨型塗膜の抵抗係数 (3ヶ月経過後) 初期粗度大のSF5Rの抵抗が大幅に低下 他の塗膜面の抵抗は微増傾向 0.0036 0.0035 0.0034 0.0033 0.0032 Ct 0.0031 0.003 0.0029 0.0028 0.0027 00/12/18 RF1 SF1 SF3 SF5 SF5R 0.0026 2 3 4 5 6 7 Rn 37 8 9 10 11 12 +6 [10 ] 塗膜面摩擦抵抗の経時変化 3.5 3.4 3.3 RF1 SF1 SF3 SF5 SF5R SW1 SW3 3.1 3.0 2.9 2.8 2.7 2.6 2.5 Sep Oct Nov Dec 平均粗度Rzの経時変化 100 5.5kt 10.1kt 90 SF1 80 SF1R 70 SF3 60 SF5 50 Rz(m) Ct×1000 3.2 SF5R 40 SF5RR 30 20 10 0 0 100 38 Day 200 平均粗度Rzと抵抗係数の相関 4 at Rn=8,000,000 5.5kt 10.1kt SF–1 SF–1R SF–3 1000Cf SF–5 SF–5R SF–5RR Estimated 3 4 5 10 10 L/Rz 平均摩擦応力の比較 -自己研磨型塗膜の場合- SF5R Series 0.0036 0.0035 0.0034 0.0033 0.0032 Ct 0.0031 0.003 0.0029 0.0028 0.0027 Exp.(Rmax) Cal. 00/09/11(87m) Ke=115m 00/10/10(79m) Ke= 75m 00/11/13(74m) Ke=60m 00/12/18(59m) 0.0026 2 3 4 5 6 7 Rn 39 8 9 10 11 12 +6 [10 ] 最大粗度Rzmaxと 等価砂粗度Κeの相関 200 180 160 140 Ke(m) 120 100 at Rn=8,000,000 5.5kt 10.1kt 80 SF–1 SF–1R SF–3 SF–5 SF–5R SF–5RR 60 40 20 0 0 20 40 60 80 100 120 140 160 180 200 Rzmax(m) ΔCFとレイノルズ数の関係 Whiteの式を用いて等価砂粗度KeからΔCFを推定 相対粗度高さ一定の場合のΔCFの変化を表示 0.002 Ke/L=1×10 –5 Ke/L=5×10 CF 0.001 Ke/L=1×10 –5 –6 –6 Ke/L=5×10 –7 0 6 10 Ke/L=1×10 7 8 10 10 Rn 40 10 9 10 10 実船におけるΔCFの推定 船速15ノット、海水温度15℃と仮定 等価砂粗度高さを一定とした場合のΔCFを表示 SF5Rの研磨によるΔCFの低下量は0.0002程度 0.0008 Ke=200m CF 0.0006 ITTC1978 Ke=100m 0.0004 Ke=50m Ke=25m 0.0002 0 100 200 300 L(m) 撥水性塗膜の摩擦抵抗係数 (初期状態) 0.0036 0.0035 0.0034 0.0033 0.0032 Ct 0.0031 0.003 0.0029 0.0028 0.0027 00/09/11 RF1 SW1 SW3 0.0026 2 3 4 5 6 7 Rn 41 8 9 10 11 12 +6 [10 ] 撥水性塗膜の摩擦抵抗係数 (3ヶ月経過状態) 0.0036 0.0035 0.0034 0.0033 0.0032 Ct 0.0031 0.003 0.0029 0.0028 0.0027 00/12/18 RF1 SW1 SW3 0.0026 2 3 4 5 6 7 Rn 8 9 10 11 12 +6 [10 ] 生物付着による摩擦抵抗増加 直径・高さとも1mm の円柱状の生物(セル プラ)が10cm角の 範囲に約40個付着 42 生物付着影響の推定例 u/U u/U 0.4 0.4 RF1 1 RF1 2 RF1 3 SF1(未使用、傷あり) SF5 SF5R SW3 0.3 RF1 1 RF1 2 RF1 3 SF1(未使用、傷あり) SF5 SF5R SW3 0.3 0.2 1 1.5 2 1 r/R 1.1 1.2 1.3 r/R 1.4 (c) 計測速度分布(拡大) (a) 計測速度分布 u/U u/U 0.4 0.4 0μ 50μ 100μ 0μ 50μ 100μ •セルプラの付 着による影響 を等価砂粗度 Keで評価する と100μmに 相当する 0.3 0.3 0.2 1 1.5 1 2 1.1 1.2 1.3 r/R 1.4 r/R (b) 計算速度分布 (d) 計算速度分布(拡大) トムズ効果の検証 -回転円筒試験装置による計測例- 0.005 1st 0.0045 2nd PEO3(0ppm) PEO3(118ppm) Ct 0.004 PEO3(350ppm) 分子量100万のPE O水溶液で最大18% の抵抗低減を確認 0.0035 0.003 0.0025 0.002 1 2 3 4 5 6 7 Re 8 9 43 10 11 12 13 [10 +6 ] トムズ効果の検証 -効果の持続性- 7 6.9 6.8 長時間にわたって剪 断力を加えると、摩 擦抵抗低減効果が消 失する ↓ 添加物の物性が変化 する? PEO3(0ppm) 6.6 PEO3(118ppm) 6.5 6.4 6.3 6.2 6.1 6 5.9 0 10 20 Time(min) 30 40 トムズ効果の検証 -物性値との関係- せん断率大で粘性係数小 (Stress Thinning) ↓ 摩擦抵抗低減効果あり 0.0014 せん断粘性係数(Pa・s) Q(Nm) 6.7 0.0012 0.001 せん断率大で粘性係数大 ↓ 摩擦抵抗低減効果なし 0 100 44せん断率(1/s) 200 まとめ -塗膜面と摩擦抵抗の関係- • 自己研磨型塗膜は研磨作用により表面粗度が 低下し初期状態より抵抗が低減する • 自己研磨型塗膜の抵抗が滑面の抵抗を下回る ことはない • 撥水性塗膜には摩擦抵抗低減効果は認められ ない • 強い撥水性があっても生物付着は生じる • 回転円筒試験の結果から塗膜面の等価砂粗度 を決定すれば、これを用いて実船スケールにお ける摩擦抵抗の増減量を推定することができる 45 勝井委員の発表資料 勝井「粗度影響を考慮した平板摩擦抵抗の算定について」では勝井委員が行なっている後 流関数を考慮した摩擦抵抗計算法に粗度の影響を入れた方法が説明された。 勝井「等価砂粗度による平板摩擦抵抗係数の増加量―計算結果の表示について」では勝井 委員が行なっている後流関数を考慮した摩擦抵抗計算法に粗度の影響を入れた方法の結果 が説明された。 勝井「後流関数を考慮した平板摩擦の粗度影響について」後流関数を考慮していない阪大 の方法との比較が示された。 46 摩擦抵抗低減ストラテジ研究委員会資料 平成 22 年 1 月 21 日 粗度影響を考慮した平板摩擦抵抗の算定について 神戸大学大学院 海事科学研究科 勝井 辰博 1. 平板摩擦抵抗係数 C F の算定手法 (1) 運動量積分式 二次元の圧力勾配のない平板周りの流れを考えると,運動量積分公式は以下のようになる. τ dθ 1 = w 2 = cf dx ρU 2 θ :運動量厚さ,τ w :壁面せん断応力,ρ:流体の密度, U :一様流速, c f :局所摩擦抵抗係数 (1) 運動量厚さの定義は θ ≡∫ δ 0 u u 1 − dy U U (2) u :主流方向の流速,δ:境界層厚さ これを x = 0 すなわち平板前縁で運動量厚さ θ が 0 となる条件のもと積分すれば x θ= x ∫0 τ w dx 1 = CF x 21 2 2 ρU x 2 (3) C F :平板摩擦抵抗係数 となる.つまり,運動量厚さ θ を定義する乱流境界層内の速度分布が分かれば,(2),(3)式より 平板摩擦抵抗係数 C F を算定することが可能となる. (2) 平板の乱流境界層内速度分布 平板の乱流境界層内速度分布は Fig.1 に示すような摩擦速度を用いた相似則が知られている.図 中に示したように境界層は I.粘性応力が卓越する粘性底層,II.粘性応力とレイノルズ応力が 同程度の Buffer 層,III.レイノルズ応力が卓越する対数領域から外層,の 3 領域に分類され, それぞれの領域で速度分布は異なる.粘性底層,Buffer 層の速度分布が C F に与える影響は微小 である.そこで本研究では,境界層内で,レイノルズ応力が卓越する対数領域から外層域の速 度分布を境界層内速度分布として用いた.その領域での速度分布は,Coles Law と呼ばれ,以 下のような式で与えられる. Coles Law ( ) + 1 Π δ + y+ + w + − F u = ln y + C + κ κ δ + + w y = 1 − cos π ⋅ y δ+ δ + + + u = u Uτ , y = Uτ ⋅ y ν ,δ + = Uτ ⋅ δ ν , ( ) 47 (4) 摩擦抵抗低減ストラテジ研究委員会資料 平成 22 年 1 月 21 日 ( ) U τ = τ w ρ :摩擦速度, κ = 0.41 :カルマン定数, ν :動粘性係数, C = 5.0 :(平板のとき), y :平板からの距離, Π (δ + ) = 0.62 − 1.21exp(− δ + 290 ) :後流パラメタ, w :後流関数 ここで式中 F は,粗度によって境界層内の速度分布が一様に減速する効果を表しており,粗面 の特性に応じて変化する.以後この F を F = ∆u U τ とし,粗度関数と呼ぶことにする. 30 Ⅰ Ⅱ Ⅲ u+ 20 Ⅰ: linear sublayer 10 Ⅱ: buffer layer Ⅲ: log region and outer layer 0 100 101 102 y+ 103 Fig.1 Similarity law of velocity profile in turbulent boundary layer. (3) 粗度関数 砂粗面的性質をもつ粗面の場合は摩擦速度 U τ と粗度高さ k で表される粗度レイノルズ数 k + (= U τ ⋅ k ν ) の増加とともに粗度関数 ∆u U τ が大きくなる.砂粗面の粗度関数 ∆u U τ は, White3)による実験式が与えられており,粗度レイノルズ数 k + が境界層内速度分布に与える影響 は(2-1-2-1)式のように表される. ∆u / U τ = 1 κ ( ln 1 + 0.3 ⋅ k + ) (5) この式を(4)式の F に代入することにより,砂粗面での,粗度影響を含む平板乱流境界層内速度 分布が得られる. (4) 平板摩擦抵抗係数を求めるための微分方程式 (4), (5)式より砂粗面の平板乱流境界層内速度分布式は(6)式のように表わされる. u+ = 1 κ ( ) ln y + + C + ( ) w y Πδ+ κ + 1 + δ + − κ ln 1 + 0.3 ⋅ k ( y+ w + δ ) y+ = 1 − cos π ⋅ + δ 平板乱流境界層の外端 y = δ で,流速 u が一様流速 U となるから ( ) U 1 2Π δ + 1 = ln δ + + C + − ln 1 + 0.3 ⋅ k + Uτ κ κ κ ( ) ( (7)式から(6)式を引けば,速度欠損は 48 ) (6) (7) 摩擦抵抗低減ストラテジ研究委員会資料 平成 22 年 1 月 21 日 ( ) y+ Πδ+ U −u 1 + = − ln y + / δ + + − 2 w κ κ Uτ δ ( ) (8) となる。両辺に u/Uτ を加え、さらに両辺を U/Uτ で割ると ( ) y + Πδ+ U u 1 + = − ln y + / δ + + 2 − w κ Uτ Uτ κ δ y + U Πδ+ u Uτ Uτ 1 + 1= ln y + / δ + + τ 2 w − − Uτ U U κ U κ δ すなわち速度欠損則は,無次元摩擦速度 σ (= U τ U ) を用いて, σ Π σ ⋅ u + = 1 + ln η + − σ ⋅ ⋅ 2 − w η + ( ) ( κ ただし,η + ( ) ) ( ) κ ( ( )) (9) (10) (11) + ≡ y+ δ + (2)式で定義される運動量厚さ θ は定義式において y を y+ に変数変換すれば u = σ ⋅ u , y + = U τ y /ν ( dy = ν / U τ dy + )より 1 δ+ θ = + ∫ σ ⋅ u + (1 − σ ⋅ u + )dy + δ δ (12) 0 と変換できる.同様に(3)式は R ⋅σ θ 1 = CF x + δ 2 δ (13) ただし, R x = Ux /ν :平板長さ x に対するレイノルズ数 となる.よって(12),(13)式より ∫ δ+ 0 u + (1 − σ ⋅ u + )dy + = 1 C F Rx 2 (14) の関係が得られる.左辺の積分を計算することで,(14)式は F1 (δ + ) − σ ⋅ F2 (δ + ) = 1 C F Rx 2 (15) ただし, F1 (δ + ) = (1 + Π(δ )) , F (δ ) = κ 1 + + 2 π sin θ 0 θ Si(π ) = ∫ 1 3Π 2 Si (π ) 2 + + 2Π 2 1 + 2 2 π κ dθ :積分正弦関数 と表される. ここで,無次元摩擦速度 σ には,局所摩擦抵抗係数 c f との間に σ≡ Uτ = U τw 1 = cf 2 2 ρU (16) という関係がある.また,局所摩擦抵抗係数 c f と平板摩擦抵抗係数 C F には,(3)式の微分と(1) 式から dθ 1 dC F 1 1 U dC F 1 1 = x + CF = x + CF = c f dx 2 dx 2 2 ν dRx 2 2 となり、 49 摩擦抵抗低減ストラテジ研究委員会資料 平成 22 年 1 月 21 日 c f = C F + Rx ⋅ dC F dRx (17) という関係が得られる.よって無次元摩擦速度 σ は C F + Rx ⋅ σ = dC F dR x (18) 2 と表される.(15),(18)式より, C F + Rx ⋅ ( ) F1 δ + − が成り立つ.ここで, RnL dC F dRx ( ) 1 CF Rx 2 ⋅ F2 δ + = (19) 2 = ln (R x ) という変数変換を行うと, dC F 1 dC F = dRx R x dRnL (20) となることから, dC F dRnL X = (21) とおけば,(19)式から ( ) ( ) f X , δ + = F1 δ + − CF + X 1 ⋅ F2 δ + − C F ⋅ exp(RnL ) = 0 2 2 ( ) (22) のように砂粗面での平板摩擦抵抗係数 C F を算定する微分方程式が得られる. + しかしながら,この式は X = dC F / dRnL と δ の2つの未知数を持つ方程式であるから,これだけで は,粗面での平板摩擦抵抗係数 C F を算定することができない.そこで,平板乱流境界層外端で,流 速が一様流速となることを考慮すれば,(7)式より,無次元摩擦速度 σ を用いて,(23)式が成り立つ必 要がある. 1 = σ 1 κ ( ) ln δ + + C + ( ) − 1 ln (1 + 0.3 ⋅ k ) κ κ 2Π δ + + (23) + また,式中,粗度レイノルズ数 k は,定義式から無次元摩擦速度 σ を用いて U τ Ux k U τ R k L k k = ⋅ R x ⋅ ⋅ = σ ⋅ R x ⋅ n ⋅ = σ ⋅ Rn ⋅ U ν x U x L ν Rx L L UL ただし, R n = :平板長さに対するレイノルズ数 ν k+ = Uτ k = となることから,(23)式は 1 σ = 1 κ ( ) ln δ + + C + ( ) − 1 ln1 + 0.3 ⋅ σ ⋅ R 2Π δ + κ κ n ⋅ (24) k L (25) となる.この式に(18)を代入し,先ほど用いた変数変換を行うことで, ( ) g X ,δ + = ( ) CF + X 2 1 2Π δ + 1 k + − ln δ − C − + ln1 + 0.3 ⋅ ⋅ Rn ⋅ = 0 CF + X κ κ κ 2 L ( ) (26) + を得る.(26)式も(22)式同様 X = dC F / dRnL と δ の2つの未知数を持つ方程式であり, k / L を与え + れば,(26)式と(22)式を連立させて解くことで,各レイノルズ数に対して dC F / dRnL と δ が得られ るから順次 dC F / dRnL を積分すれば平板摩擦抵抗係数が得られる. 50 摩擦抵抗低減ストラテジ研究委員会資料 平成 22 年 1 月 21 日 2. 平板摩擦抵抗係数に与える粗度影響の計算例 (1) 計算条件 平板長さ:L=300 [m] 粗度高さ:k=0, 0.03, 0.3, 3, 30, 150 [µm] 計算レイノルズ数:Rn=1.0*105 ~ 1.0*109 (2) 計算結果 1.4 k=0 (smooth) k=0.03[µm] k=0.3 [µm] k=3 [µm] k=30 [µm] k=150 [µm] 1.2 CF*102 1 0.8 0.6 0.4 0.2 0 105 106 107 108 109 Rn Fig. 2 Frictional resistance coefficient of flat plate with sand roughness 0.5 k=0 (smooth) k=0.03[µm] k=0.3 [µm] k=3 [µm] k=30 [µm] k=150 [µm] CF*102 0.4 0.3 0.2 0.1 0 107 108 109 Rn Fig.3 Frictional resistance coefficient of flat plate with sand roughness in high Reynolds number. 51 ➼౯◁⢒ᗘࡼࡿᖹᯈᦶ᧿ᢠಀᩘࡢቑຍ㔞 㸫ィ⟬⤖ᯝࡢ⾲♧ἲࡘ࠸࡚ ⚄ᡞᏛᏛ㝔ᾏ⛉Ꮫ◊✲⛉ ㎮༤㸪Ἠ ༟ᚿ G G G G G 5H ⯪㏿୍ᐃ࡛ᩚ⌮ G G G G G G G N/ />P@ 5H N N N N />P@ 5H 8 >NQRW@ >ȣP@ >ȣP@ >ȣP@ >ȣP@ >ȣP@ >ȣP@ >ȣP@ >ȣP@ 8 >NQRW@ N N N N N N N N 8 >NQRW@ >ȣP@ >ȣP@ >ȣP@ >ȣP@ Ǽ&) N N N N Ǽ&) 8 >NQRW@ 5Q 5Q 5Q 5Q 5Q 5Q 5Q Ǽ&) Ǽ&) Ǽ&) N/ N/ N/ N/ N/ Ǽ & ) N/ ࡛ᩚ⌮ N㸸◁⢒ᗘ㧗ࡉ㸪/㸸⯪㛗 >ȣP@ >ȣP@ >ȣP@ >ȣP@ />P@ 5H />P@ N ȣP 5Q 5Q 5Q 5Q 5Q ( ( ( ( ( N ȣP &) 5Q 5Q 5Q 5Q 5Q ( ( ( ( ( &) 8>PV@ 52 8>PV@ 5H 5Q 5Q 5Q 5Q 5Q N ȣP ( ( ( ( ( N ȣP ( ( ( ( ( &) &) 5Q 5Q 5Q 5Q 5Q 8>PV@ 8>PV@ 5Q 5Q 5Q 5Q 5Q N ȣP ( ( ( ( ( &) &) 5Q ( 8 8 8 8 8 >NQRW@ >NQRW@ >NQRW@ >NQRW@ >NQRW@ 8>PV@ N>ȣP@ 5Q ( 8 8 8 8 8 >NQRW@ >NQRW@ >NQRW@ >NQRW@ >NQRW@ &) &) 5Q ( 8 8 8 8 8 >NQRW@ >NQRW@ >NQRW@ >NQRW@ >NQRW@ N>ȣP@ &) 5Q ( 8 8 8 8 8 >NQRW@ >NQRW@ >NQRW@ >NQRW@ >NQRW@ N>ȣP@ 53 N>ȣP@ 摩擦抵抗低減ストラテジ研究委員会資料 平成 22 年 10 月 8 日 後流関数を考慮した平板摩擦の粗度影響について - 阪大の方法との比較 神戸大学大学院海事科学研究科 勝井 辰博 1. 速度一定の場合 (実線:神戸大学、破線:大阪大学) 計算条件 速度:U=8.0,12.0,16.0,20.0,24.0 [knot] 粗度高さ:k=0.0,100.0,160.0,240.0,320.0,400.0 [µm] 計算レイノルズ数 :Rn=1.0*106 ~ 1.0*1010 0.012 k=400.0μm k=400.0μm k=320.0μm k=320.0μm k=240.0.μm k=240.0μm k=160.0μm k=160.0μm k=100.0μm k=100.0μm k=0.0μm k=0.0μm U=8.0(knot) 0.01 CF 0.008 0.006 0.004 0.002 106 107 108 109 1010 Rn 0.012 k=400.0μm k=400.0μm k=320.0μm k=320.0μm k=240.0μm k=240.0μm k=160.0μm k=160.0μm k=100.0μm k=100.0μm k=0.0μm k=0.0μm U=12.0(knot) 0.01 CF 0.008 0.006 0.004 0.002 106 107 108 Rn 54 109 1010 摩擦抵抗低減ストラテジ研究委員会資料 平成 22 年 10 月 8 日 0.012 k=400.0μm k=400.0μm k=320.0μm k=320.0μm k=240.0μm k=240.0μm k=160.0μm k=160.0μm k=100.0μm k=100.0μm k=0.0μm k=0.0μm U=16.0(knot) 0.01 CF 0.008 0.006 0.004 0.002 106 107 108 109 1010 Rn 0.012 k=400.0μm k=400.0μm k=320.0μm k=320.0μm k=240.0μm k=240.0μm k=160.0μm k=160.0μm k=100.0μm k=100.0μm k=0.0μm k=0.0μm U=20.0(knot) 0.01 CF 0.008 0.006 0.004 0.002 106 107 108 Rn 55 109 1010 摩擦抵抗低減ストラテジ研究委員会資料 平成 22 年 10 月 8 日 0.012 k=400.0μm k=400.0μm k=320.0μm k=320.0μm k=240.0μm k=240.0μm k=160.0μm k=160.0μm k=100.0μm k=100.0μm k=0.0μm k=0.0μm U=24.0(knot) 0.01 CF 0.008 0.006 0.004 0.002 106 107 108 109 1010 Rn 2. 平板長さ一定の場合(実線:神戸大学、破線:大阪大学) 計算条件 平板長さ:3.0[m] 速度:U=1.0~10.0 [knot] 粗度高さ:k=0.0,100.0,160.0 [µm] 計算レイノルズ数:Rn=1.0*106 ~ 2.0*107 0.006 k=0.0μm(OSAKA) k=100.0μm(OSAKA) k=160.0μm(OSAKA) k=0.0μm(KOBE) k=100.0μm(KOBE) k=160.0μm(KOBE) CF 0.005 0.004 0.003 0.002 106 Rn 56 107 日夏、川島委員の発表資料 NMRI 流体設計系「平行平板曳航法による平板の摩擦抵抗評価」では、様々な水槽試験で の影響を除去して高精度に平板摩擦抵抗を計測する方法について示され、適用例が示され た。 日夏、川島「摩擦応力計測法について」では摩擦応力の計測法について広範囲にレビュー した結果を紹介した。 57 平行平板曳航法による 平板の摩擦抵抗評価 海上技術安全研究所 流体設計系 研究の背景と目的 船舶の全抵抗の内、摩擦抵抗成分が50%∼80%を占めるため、 摩擦抵抗の低減が可能であれば、船舶の省エネ化に有効 NEDOプロジェクト 海水摩擦抵抗を低減する船舶用塗料の基礎技術の研究開発 ・塗料の種類による摩擦抵抗の差を精密に評価したい ・1%程度の摩擦抵抗の差を正確に評価することが目標 58 1 開発目標 ●塗料の種類による摩擦抵抗の差を精密に評価する。 ●外部流れでの摩擦抵抗を評価する。 ●発達した乱流境界層での摩擦抵抗を評価する。 ●なるべく実船に近いレイノルズ数で摩擦抵抗を評価する。 ●実船と同程度の局所摩擦応力(剪断応力)の条件で摩擦抵抗 を評価する。 ●1%程度の摩擦抵抗の差を評価可能とする。 35 実船14kt 30 平板4.5m/s τw 25 Re = 平板4m/s 20 L ×V µ L :代表長さ 10 V :速度 5 µ :動粘性係数 15 0 0 50 100 150 200 250 300 350 L (m) 長水槽での摩擦抵抗評価における誤差要因 長水槽における曳航試験で摩擦抵抗を評価する場合の誤差要因 ●計測系起因の誤差 ・検力計の精度 ・計測装置の可動部、摺動部の摩擦、変形部のバネ定数等の誤差 ・計測値の振動と平均値の求め方 ●水槽試験起因の誤差 ・静振、残留、水温の不均一と変化、レール高さ、速度制御 ●抵抗成分の影響 ・造波抵抗成分、形状抵抗成分、浸水表面積に占める被検部面積 の割合、造波による浸水表面積の変化 ●被試験体の影響 ・模型の製作精度、模型の設置状態 ・乱流遷移の安定性 59 2 平行平板曳航法の精度向上のための工夫 ●2枚の試験用平板を同時に曳航・計測することで、水槽内の残流、 静振、温度勾配、レール高さの変動、曳航台車の速度変動、計測区 間の設定などの誤差要因が、両平板におなじように影響を与える ようにして、緩和させた。 ●試験用平板は前後の板バネを介してブランコ式にぶら下げることで、 摩擦・摺動抵抗の影響を無くし、装置起因のヒステリシスが小さくなる ようにした。 ●試験用平板は、高精度圧延アルミニウム板に、精密に機械加工した 整流部を取り付ける構造として、個体差により生じる誤差を小さくした。 ●長さ2.25m厚さ10mmのごく薄い平板模型を用いることで、 造波抵抗成分、形状抵抗成分が極力小さくなるようにした。 ●流体力学的な干渉の影響が無視できる距離をCFDにより計算して 平板の間隔を2.0mとした。 ●後部整流覆いに設置した高精度水温計で水温を常時モニタ。 平行平板曳航法による摩擦抵抗計測装置 試験用平板 全長 2250mm(内前後250mmは、円弧翼型フェアリング) 全高 1160mm(喫水760mm) 厚さ 10mm 平板の間隔 2000mm 検力計 抵抗計測用1分力計2台(定格200N、誤差0.02%) 平板の固定方法 平板の進行方向の軸のみ自由、他は拘束 吊り下げ方式 板バネ方式 乱流促進 スタッド方式(2mm角、高さ2mm、間隔10mm、1条) 試験平板の取付調整 レーザーシート光を基準面とする 喫水線 平板間距離2000(mm) 760(mm) 2250(mm) 側面図 正面図 60 3 摩擦抵抗計測方法模式図 計測方法模式図(抵抗計測時) 進行方向 検力計 板バネ 曳航ロッド 試験用平板 側面図 検力計と曳航ロッドの取り付け状態 検力計 曳航ロッド 61 4 乱流促進装置とブランコの板バネ 乱流促進装置 (2mm角立方体を 10mm間隔で配置) 板バネ 前部整流覆いと乱流促進装置 平板をつり下げる板バネ 試験用平板取り付け調整方法 レーザーシート光を 基準面にして試験用平板 を取り付け・調整する。 計測レールの駒を基準に レーザーシート光で基準面をつくる 平板とレーザーシート光の 距離を計測する 62 5 計測装置水槽設置状態 乱流状態の確認 0.005 CT, CF 全抵抗係数、摩擦抵抗係数 0.0045 0.004 0.0035 0.003 0.0025 0.002 CT (FAPB) CT (FBPA) CF (Shoenherr) CF*1.03 0.0015 0.001 0.0005 0 0.0E+00 2.0E+06 4.0E+06 6.0E+06 8.0E+06 1.0E+07 1.2E+07 Re Shoenherrの式で求められる摩擦抵抗係数との比較 63 6 抵抗成分の分離 RT = RR + RFleading −edge + RFtest − surface + RFtrailing −edge + RFbottom −end RR :剰余抵抗(造波抵抗及び形状抵抗) RT :全抵抗 RFtest − surface :検査面の摩擦抵抗 RFleading −edge :前部整流覆の摩擦抵抗 RFtrailing −edge :後部整流覆の摩擦抵抗 RFbottom −end :下部整流覆の摩擦抵抗 喫水線 125mm 1150mm 750mm 乱流促進 検査面 125mm 2000mm 10mm 前部整流覆 後部整流覆 下部整流覆い 抵抗成分の割合 100% 90% 80% 70% 剰余抵抗 60% 整流覆摩擦抵抗部分 50% 試験部摩擦抵抗成分 40% 30% 20% 10% 0% 0.5 1 1.5 2 2.5 3 3.5 4 4.5 試験速度(m/s) 64 7 計測装置の精度① 検力計を装置に取り付けた状態での精度を以下に示す。 精度の確認は平板を取り付けた状態で、校正用プーリーを 用いて定格容量の490Nまで実施。 右検力計 490N 直線性 ヒステリシス (%) (%) 0.07 0.04 -0.03 左検力計 490N 0.06 -0.06 定格 0.06 計測装置の精度②(精度確認試験) ・試験対象 同一寸法、同一形状の無塗装アルマイト地肌の基準板 ・抵抗試験 速度範囲 0.5m/s∼4.5m/s Re数:1×106∼1×107 ・繰り返し試験 速度:4.0m/s 試験回数:10回 65 8 計測装置の精度③整流部の固有抵抗 整流部、板の交換による整流部固有抵抗差の確認 FA:フェアリングA、FB:フェアリングB、PA:平板A、PB:平板B 2.00% FBPA-FAPB FAPA-FBPB(フェアリング交換) FBPA-FAPB(フェアリング戻し) FAPB-FBPA(平板左右交換) 全抵抗の差[%] 1.50% 1.00% 0.50% 0.00% -0.50% 0 1 2 3 4 5 -1.00% -1.50% Vm[m/s] 左右の前部フェアリングの固有抵抗の差が0.3%程度あることが判った。 計測装置の精度②繰り返し試験結果① 同一形状・材質の試験用平板2枚の繰り返し試験結果(4m/s) 計測された全抵抗値の差は0.18%の範囲に分布 1.00% 0.80% FAPB-FBPA(4m/s) dR/R[%(15℃)] 左右平板の抵抗差(%) 0.60% 0.40% 0.18% 0.20% 0.00% -0.20% 0 1 2 3 4 5 6 7 8 9 10 11 -0.40% -0.60% -0.80% -1.00% Test Number 66 9 計測装置の精度③繰り返し試験結果② 全抵抗値の分布の範囲は、左側平板で0.46%、右側平板で0.45% 左右の平板を同時に計測することにより、試験状態の相違が緩和されていることが判る 1.0% Right plate(4m/s) Left plate(4m/s) 0.6% 0.4% 0.2% 0.0% -0.2% 0.45% 0 0.46% 1 2 3 4 5 6 7 8 9 10 11 -0.4% -0.6% -0.8% -1.0% Test Number 計測装置の精度④平板の脱着 同一形状・材質の試験用平板の検査面を左右取り替えて計測 平板の脱着による差は最大で0.1%程度 0.50% FAPA-FBPB 0.45% dR/R[%] 左右平板の抵抗差(%) 平板抵抗値の平均値との差(%) 0.8% 0.40% FAPB-FBPA 0.35% 0.1%程度 0.30% 0.25% 0.20% 0.15% 0.10% 0.05% 0.00% 5.0E+06 6.0E+06 7.0E+06 8.0E+06 9.0E+06 1.0E+07 Re 67 10 舶用塗料の評価①(試験条件) ・試験対象 無塗装アルマイト地肌の基準板 加水分解型塗料A塗装板 シリコン系塗料B塗装板 サンドブラスト加工粗度板 ・速度範囲 0.5m/s∼4.5m/s Re数:1×106∼1×107 加水分解塗料A シリコン系塗料B 舶用塗料の評価②(塗膜の厚みの影響の補正) depth (m) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.75 average 9.99 10.00 10.00 10.00 10.00 10.00 10.00 Bare plate 10.00 10.00 thickness 10.56 10.50 10.54 10.48 10.49 10.47 10.47 10.49 10.50 (mm) Paint A Paint B 10.97 10.98 10.93 10.94 10.92 10.92 10.94 10.98 10.95 0.1 With 12 sheets 0.09 0.08 DCR/CR 0.07 0.06 0.05 With 6 sheets 0.04 0.03 0.02 0.01 0 0 0.2 0.4 0.6 Additional thickness of the plates (mm) 0.8 1 DCR = CRsheets − CR0 CR0:厚みが付加されていない状態 CRsheets:厚みが付加された状態 での剰余抵抗係数 での剰余抵抗係数 68 11 舶用塗料の評価③(摩擦抵抗計測結果) 0.0041 Bare plate 1 (vs Roughness) Bare plate 2 (vs Paint A) 0.0039 Bare plate 3(vs Paint B) 0.0037 Paint A (vs Bare plate) Paint A (vs Paint B) CF 0.0035 Paint B (vs Bare plate) 0.0033 Paint B (vs Paint A) Roughness (vs Bare plate) 0.0031 0.0029 0.0027 0.0E+00 2.0E+06 4.0E+06 6.0E+06 8.0E+06 1.0E+07 1.2E+07 Re 舶用塗料の評価④(同時計測の摩擦抵抗の評価) 1.035 1.03 1.025 CF/CF 1.02 1.015 Roughness/Bare plate Paint A/Bare plate Paint B/Bare plate Paint B/Paint A 1.01 1.005 1 0.995 0.99 0.0E+00 2.0E+06 4.0E+06 6.0E+06 8.0E+06 1.0E+07 1.2E+07 Re 69 12 舶用塗料の評価④(試験平板の表面粗度) 走査型共焦点レーザー顕微鏡 非接触レーザー変位計 2.5mm×1.9mm 30mm×30mm 2Ra Rzjis Rz Rz Paint A 3.22 6.48 10.48 100 粗度(μm) Paint B 0.74 1.64 2.62 106 Roughness plate 15.04 33.86 48.59 61 測定範囲 粗度定義 粗度と摩擦抵抗の関係(Schlichtingの図表から) 走査型共焦点レーザー顕微鏡 非接触レーザー変位計 2.5mm×1.9mm 30mm×30mm 2Ra Rzjis Rz Rz Paint A 6.99E+05 3.47E+05 2.15E+05 2.25E+04 粗度(k/L) Paint B 3.04E+06 1.37E+06 8.59E+05 2.12E+04 Roughness plate 1.50E+05 6.65E+04 4.63E+04 3.69E+04 測定範囲 粗度定義 1.35 CF(rough)/CF(smooth) 1.3 1.25 1.2 1.15 1.1 1.05 1 0.95 0.9 0.E+00 5.E+04 1.E+05 2.E+05 2.E+05 3.E+05 L/k 70 13 まとめ ・左右の平板を同時に計測することにより、水槽試験に つきものの計測毎の条件の相違が緩和され、抵抗の差 がより精度良く評価できる。 ・繰り返し試験の結果、左右平板の抵抗差の再現性は 非常に高い。 ・摩擦抵抗の差1%以下の2種類の船舶用塗料の摩擦抵抗 を評価できた。 ・塗膜の表面粗度は、波長の大きいうねり成分ではなく、 波長の短い粗度で評価する必要がある。 謝辞 本研究は (独)新エネルギー・産業技術総合開発機構による 「海水摩擦抵抗を低減する船舶用塗料の基礎技術 の研究開発」の一部として実施しました。 ここに謝意を表します。 71 14 摩擦応力計測法について 摩擦抵抗低減ストラテジー委員会 平成23年1月21日 海技研 日夏宗彦、川島英幹 摩擦応力計測法(チャンネル流)についてのレビュー 摩擦応力計測法について、1950年代から70年代にかけて活発に行われた。 今回の紹介ではチャンネル流にとらわれず、摩擦応力計測法に関する過去の文献から、 以下の4件を取り上げて、紹介することとする。これらの論文では、摩擦応力計測法に関 するレビューや考察が詳細に記述されており、一読しておく価値のある文献と思われる。 1)Direct Measurements of Skin Friction, b y S.Dhawan, NACA Report 1121 (1953) 2)Skin-Friction Measurements in Incompressible Flow, by D.W.Smith & J.H.Walker NACA-TN-4231, (1958) 3) Calibration of the Preston tube and limitations on its use in pressure gradients, by V.C.Patel, JFM vol23, part 1, 185-208 (1965) 4) The Measurement of Skin Friction in Turbulent Boundary Layers with Adverse Pressure Gradients, by K.C.Brown, P.N.Joubert, JFM Vol.35 part 4, 737-757 (1969) 72 摩擦応力計測法(チャンネル流)についてのレビュー 我が国(船舶系)においても下記のような摩擦応力計測に関する研究が行われている。 (今回は紹介を割愛した) 1)A New Skin Friction Meter of Floating-Element Type and the Measurements of Local Shear Stress by T.Hotta, JSNAJ Vol. 138, (1976) 2)表面粗度による抵抗増加に関する研究(第1,2報)、山崎、小野木他、造論153号 (1983)、155号(1984) 3)油膜を用いた限界流線と壁面摩擦応力の計測、奥野他、造論176号、(1994) 4)船体表面の摩擦応力分布および境界層内の2次流れに関する研究、奥野、造論139号、 (1976) なお、今回のレビューの最後に光学的手法による最近の論文を簡単に紹介した。先の英 文4件とは異なる手法であるため、新しい動向の自答という位置づけで取り上げた。 また、ここで紹介する4件の英文論文や上記の論文は著名なものばかりなので、既に読ま れた方がほとんどと思われるが、復習の意味も込めてご容赦願いたい。 Dhawan の論文 概要: 超音速域での摩擦抵抗式を求める。従来の計測法についてのレビューをした結果、直接法を採用し た。本論ではレビュー内容が詳細に述べられている。 直接法に対しても、圧縮性流体を視野に入れているので、温度計測による方法もレビューしている。 最終的には直接摩擦応力を計測する方法を採用。 Floatingタイプの方法を採用。 ・floatingタイプの場合、センサー板と支持部のgap影響は? Gap前後の境界層速度分布を計測。 影響なしと判断。 73 Dhawan の論文 微小力の計測方法: いくつかの方法があり、それぞれについてレビューの後、reactanceタイプを採用。外部の振動影響を 除去、温度変化(±20度)による出力変化がないことを確認。 計測部のピックアップ部 風胴に取り付けられた摩擦応力計測装置の詳細(図では0.2cmx2cmの受感板だが、これは音速用) (非圧縮、低音速の場合は、1.15cmx6.3cmとした) 校正では、直線性、繰り返し荷重による再現性等も確認した。 Dhawan の論文 実験時のセットアップ: 受感板が長方形のため、tilt影響による 誤差修正も考慮。 境界層速度分布計測例 層流境界層の判定として、熱線データか らTS波が検出されるか否かでも判断 74 Dhawan の論文(圧縮性の部分は省略) 摩擦応力係数の結果非圧縮の場合) 層流の場合、計測した速度分布と右図に示す圧力勾配デー タからzero圧力勾配下のデータに修正。 乱流の場合、1/7乗則で速度分布を近似 Smith & Walkerの論文 概要: Zero圧力勾配下での摩擦応力計測について詳述。3つの方法で計測。 ・境界層速度分布計測から境界層パラメータを求め運動量積分式からcfを計算。 ・直接法:floatingタイプ ・Preston管 試験のセットアップ(単位はインチ) 前縁の小孔から空気を 吹き出して、遷移させ ている 75 Smith & Walkerの論文 摩擦応力計測装置 境界層速度分布計測用の平型Pitot管 Smith & Walkerの論文 Preston管 ゼロ圧力勾配の確認 乱流境界層の見かけの始点は、d(log 2θ)/dxで決定 76 Smith & Walkerの論文 境界層速度分布計測例 乱流境界層の見かけの始点は、d(log 2θ)/dxで決定 形状係数Hとレイノルズ数の関係 Smith & Walkerの論文 77 Smith & Walkerの論文 境界層速度分布結果から運動量厚さ経由 でCFを推定した値と、Cf計測結果を積分し た結果の比較 Smith & Walkerの論文 今回の結果(tableIV)と従来の試験結果の比較 78 Smith & Walkerの論文 今回の結果(tableIV)と従来の試験結果の比較 Smith & Walkerの論文 直接摩擦応力計測法とPreston管で得た結果の比較。Preston管の方が小さいが、Prestonの 校正曲線が正しくないことが原因と考えられる。(Patelらの指摘に通じる) 79 V.C.Patelの論文 概要: Preston管による摩擦抵抗計測法を考案したPrestonが提案した式は誤差が大きい。正し い、校正式を提案する。さらに圧力勾配下で、この式がどの程度正しいか見極める。 試験方法: パイプ流れを用いる。真とする摩擦抵抗の値は圧力降下で求める。14種類のPreston管 で試験。(圧力勾配の影響小のとき) V.C.Patelの論文 境界層を下記3つの領域に分ける。て、それぞれについて定式化 それぞれについて下記のように定式化 80 V.C.Patelの論文 圧力勾配があるとき 右図のような実験装置で 実験 Prston管には新たにフェ ンスが設けられている。 フェンス前後の圧力差を 計測 前述の校正曲線が圧力 勾配下でどの程度使える のか調べルことを目的と したが、難しいことがわ かった。 圧力勾配下での速度分 布の考察を行う。 V.C.Patelの論文 Preston管の読みとフェンス前後の圧力差の読みが圧力勾配の影響を受けないとすると、これらの関係は一つの線 に乗る。しかし、実際はPreston管の読みとフェンス前後の圧力差の関係が一つの曲線に乗らない。 Preston管は圧力勾配下では摩擦力を過大評価している傾向にあるように見える。順圧力勾配下では、Preston管径 が小さくなるほど、誤差は増加。 当初の予期とは異なる。 速度分布の変化にテーマを変えた。 81 V.C.Patelの論文 Δ= 速度は0.054インチ径のピトー管で計測 摩擦応力はフェンス前後の圧力差で決める。(別途校正) 著者が導いたPreston管の使用限界 Brown & Joubertの論文 概要: 逆圧力勾配下での摩擦抵抗計測を行う。種々の方法をレビューし、その結果直接計測法を採用。 著者らの摩擦応力計測法の分類 論文では上記手法について興味深いレビューがされている。 82 Brown & Joubertの論文 直接計測法の模式図。ギャップによ る影響について考察されている。 右図は著者らの摩擦応力計測装置 Aの計測部の直径は3/4インチ ギャップは.003インチ、 Cの青銅板バネで支持、 Dはダンパーで風洞の振動影響を除 去 Brown & Joubertの論文 キャリブレーションの方法(2種類でチェック) (b)では糸の角度が必要、写真で読み取る。 試験風洞 総圧管の径:0.04インチ Preston管の径: 0.0362、0.029、0.02イ ンチ Preston管の校正係数 はPatelの結果を使用 83 Brown & Joubertの論文 結果 Clauserの方法は、次ページに示すClauserのチャートに境界層速度分布をプロットし、Cfを補間して決定 直接法とPreston管の違いは、圧力勾配によるslight secondary force、アラインメントの誤差等の影響と考えられ る。 Brown & Joubertの論文 84 Brown & Joubertの論文 圧力勾配下での結果 Preston管と速度分布から摩擦応力を決める。 圧力勾配下でのPreston管の精度限界マップ Patelの6%リミットは楽観的 Brown & Joubertの論文 直接法における圧力勾配によるsecondary forceの影響マップ 摩擦応力はPreston管の読みを用いた。 1.0のときsecondary force の影響なし 85 最近の論文より COHERENT STRUCTURES AND THEIR CONTRIBUTION TO TURBULENT INTENSITY IN TURBULENT CHANNEL FLOW S. Imayama、Y.Yamamoto、YTsuji (名大 辻先生より原稿入手) 最近の論文より uk:フリンジ速度, n:屈折率、Δh:両隣のフリンジ高さの差 h0:オイルフィ ルム端の最初のフリンジ高さ 86 戸田委員による報告の概要 1.資料1の論文と発表資料により、空気潤滑法であるがこの結果により摩擦抵抗低減が あるとプロペラ面流速(1-w)に変化があり、この場合は同じ回転数、同じ CPP 翼角 で摩擦抵抗が減ると、船速はほとんど増加せず、馬力が下がる。これを推力、トルク 計測を行なっていたため抵抗が小さくなり、1-w が大きくなっていることがわかったこ とを説明し、抵抗が下がっても単純に速度が上がる場合ばかりではないことを説明し た。これにより摩擦抵抗が変わると当然 1-w の推定もやり直す必要があること、推力 を実船で計測が可能であれば直接船体抵抗に関連するものが取られるということを説 明し、燃料消費や馬力での検討より少し細かい内容が分かることを説明した。 2.資料2の論文と発表資料(報告書では省略)により、塗膜の種類によっては同じような 幾何学敵粗度であっても、抵抗が異なる場合があること、かなり平滑面に近づくよう な場合もあることが紹介された。回転円筒装置と 3m の模型船を使った検討で、ある種 の親水性塗料では浸漬後計測すると等価砂粗度がかなり小さくなり、この等価なもの を用いて実船を推定した結果なども示された。またこの推定により同じ等価砂粗度高 さで長さを変化した時の変化を ITTC の手法と比較して説明した。現在の ITTC の相関 に関するものと粗度に関するものの粗度の部分とは少し異なる傾向があることを示し た。 3.資料3のパワーポイントにより、粗度の影響を考慮した境界層計算を行い、等価砂粗 度が変わる塗膜を半分塗る場合、前半でも後半でも同じことを示した。これは境界層 厚さの発達が異なるためで、資料4の空気潤滑でも同じことが得られることやこれは 青雲丸の実験でも見られたことなどが紹介された。 4.資料4により大学のような専門家がいないところでは浮かす単純船型模型による実験 が今までの経験上再現性が高く、その方法を様々な塗膜に行い、データベースにより さまざまな塗膜にたいする実船推定法の考察を示した。 5.深江丸のドック前後の推力、トルク計測結果を示し、推力トルク計測を行うことで汚 損の船体への影響とプロペラへの影響が分離可能ではないかという報告がなされた。 資料5 6.ITTC の表面処理委員会のレポート(資料6)と、グループディスカッションでの関連 講演の資料(資料7)が示され概略が説明され、粗度計測装置について概略が示され た。これは資料4に示した。 7.なお山盛オブザーバによる解説も戸田委員よりお願いしたのでここに資料 8 として入 れる 87 Full scale experiment for frictional resistance reduction using air lubrication method C.L. Hoang, Y. Toda, Y. Sanada Department of Naval Architecture and Ocean Engineering, Graduate school of Engineering, Osaka University Suita, Osaka, Japan the previous two experiments, the full-scale experiment using the same ship, Pacific Seagull, was carried out in 2008. This full-scale experiment was conducted by the cooperative research project with National Maritime Research Institute Japan (NMRI), Hokkaido university, Osaka university and Azuma shipping company. New Energy and Industrial Technology Development Organization (NEDO) sponsored for this project. Kodama (2008) showed a brief summary of this full-scale experiment with about 4% net fuel consumption reduction in case of full load condition and 7% in case of ballast condition. In this paper, the results from shear stress, thrust and torque measurement done by the authors are presented and considered using simple momentum integral equation of the boundary layer. The data was taken from January 6th to 11th, 2008. ABSTRACT This paper describes the full scale experiment using air lubrication method to reduce the frictional resistance. The full scale experiment with the cement carrier Pacific Seagull was conducted from January to March, 2008. Torque and thrust are decreased due to the effect of bubbles. If we assume the value of thrust deduction is constant with and without bubbles, the effect of bubbles in reducing frictional resistance or ship resistance is clearly proved by the experimental results. The maximum total resistance reduction in case of ballast condition and full load condition are about 11% and 6% respectively. The mean propeller inflow velocity was increased for with air lubrication from no air condition due to the viscous resistance reduction. This phenomenon was considered using very simple boundary layer method. KEY WORDS: EXPERIMENTAL EQUIPMENTS General Arrangement of Experimental Equipments Full scale experiment; energy saving; air The principal dimensions of Pacific Seagull ship are shown in table 1. In order to conduct the full scale experiment, the ship was equipped with experimental equipments such as blowers, cameras, ultrasonic velocity profiler (UVP), thrust and torque gauge on the propeller shaft, shear stress sensor on the hull surface and etc. lubrication; frictional resistance reduction. INTRODUCTION Air lubrication method is a promising method to reduce frictional resistance which is nearly 70% of total resistance of low speed ship. Bubbles were injected at the fore bottom part of the ship. After injection, it is expected that bubbles will cover all the bottom part downstream and take effect on local frictional resistance reduction. In 2002, the full-scale experiment was carried out in SR 239 project for the first time using the training ship Sein-maru. The net energy saving in that experiment was 2% at air injection rate 40 m3/min. Based on this result, the effect of bubbles on frictional resistance reduction of ship was proved (Nagamatsu et al. 2003). There are 5 sets of blowers, 3 on starboard and 2 on the port side. The pressure is 100 kPa. The ability of air supply of one blower is about 22 m3/min, so maximum bubble generation is 110 m3/min. Air was fed from blowers to bubble generation device using the related piping system which was installed from the main deck to the bottom of ship. Three cameras were installed at propeller plane, bubble injector position and near shear stress sensors position. The main purpose of these cameras is to capture the images of bubble when blowers were active. Three years later, in 2005, the second full-scale experiment was done using the cement carrier Pacific Seagull. This ship has a box shape hull and was equipped with blowers which could be used to supply air for bubbles. However, injected bubbles did not cover the bottom of ship sufficiently so maximum frictional resistance reduction was only 1% at air injection of 50 m3/min (Kodama et al. 2007). In order to keep bubble more efficiently inside the bottom area of ship, end plates were welded along the side end under the bottom of ship. These end plates have the same height of 0.15 m and the total length of end plates is 47.2 m. Figure 1 shows the general arrangement of equipments in full scale experiment. Overall brief description of experiments was shown in Kodama(2008). Based on the results and accumulation of experience obtained from 88 are shown in Toda et al.(2005) and the size of the fairing plate was changed to 1174x1174 mm to reduce the effect of the mound. The flat part is 400x400 mm, so the 27 mm height is reduced using 387 mm slope (less than 1/14). In this experiment, 3 sensors were installed under the bottom of the ship. 2 sensors were on the starboard and the other one was on the port side. The position of these sensors was 50 m toward the stern direction from the bubble injection position. Table 1. Principal dimensions of Pacific seagull Length over all Length between perpendiculars Breadth Depth Draft (designed full) Draft (Full experiment) Draft (ballast) in experiment Speed (service) Main engine Propeller Diameter of propeller 126.6 m 120.0 m 21.4 m 9.9 m 7.1m 7.0 m even 4.0 m (trim by stern 1.5 m) 12.4 kt 3883 kW x1 4 blades CPP 3.6 m Blower Thrust and torque gauge Bubble generator Air pipe Fig. 2 Thrust gauge and torque gauge End plate Shear stress sensor UVP transducers Camera Fig. 1 General arrangement of equipment Strain Gauge and Shear Stress Sensor To measure the thrust and torque, the strain gauges were attached on the shaft directly and to minimize the temperature effect, Hylarides method (Hylarides, 1974) with dummy plate and temperature insulation using two direction strain gauges were employed to measure thrust and torque. In figure 2, two pictures on top were focused on the images of torque gauge and thrust gauge. To minimize the misalignment, the 10mm gauge length was used for measurement as shown in Fig. 2. Here, torque gauge is the strain gauge on the left and thrust gauge is the strain gauge on the right. The remain two pictures of Fig. 2 show the installation work from the beginning when the first strain gauges were glued on propeller shaft to until the entire job have been done. Preamplifier with transmitters and batteries were tied with belts around the shaft. After finished the installation, propeller shaft was covered with thermal insulation material. The system which was constituted from these strain gauges will detect thrust, torque and temperature and transmit the measuring data as radio signals to the data acquisition system via telemeter. Fig. 3 Shear stress sensor EXPERIMENTAL RESULTS During the operation of ship, the large difference in ship speed between with and without bubble injection was not observed. The measurements were carried out for full load and ballast conditions and the blade pitch angle of controllable pitch propeller was changed to change the average speed. Figure 3 shows the images of shear stress sensor before and after it was installed under the bottom of the ship in the dockyard. As shown in the left figure, the sensing plate was held with three blade springs and frictional stress was detected by load cell. The sensing plate was made of acrylic resin and in a square shape with dimensions of 200 mm x 200 mm, 5 mm in thickness and 238 g in weight. The height of sensor was quite thin and 27 mm. The right figure shows the installation by stud bolts. After this installation, the fairing plate was installed as shown in the bottom figure. It was suitable for mounting sensor to the ship surface smoothly with fairing. Fairing plates were installed to the sensor to reduce the height difference between the sensor plate and the surrounding surface. Detailed information and structure of this sensor Figure 4 shows the example of shear stress measurement results for sensor No. 1 (near the bilge keel on starboard side) and sensor No. 2 (near the centre plane). From the figure, the clear reduction of local skin friction for both sensors can be seen at 50 m downstream from the injection point and the time lag from the start time of blower operation due to the distance from the injection point. It shows that the effect of bubbles remains whole bottom area and the larger reduction seems to be obtained in the upstream region. This result can be referred to the result obtained from the 50 m model experiment in NMRI (Kodama et 89 al. 2007). From the figure, the amount of reduction depends on the location and the reduction rate is larger near the centre plane. About 40% reduction was observed for sensor No. 2. 5 [×10 ]4 Thrust (N) Shearing Force (N) ~ 5%reduction 3 Shearing Force (N) Without bubble and with bubble by 2 blowers (No.3,4) Propeller pitch 16.2degree, ship speed 13.1kt and 12.9kt ∼20% reduction 2 ∼40% reduction Blower On Blower Off 1 Sensor No.1 t(s) ~ 5%reduction Torque(N.m) Sensor No.2 t(s) t(s) 00 500 1000 Fig. 6 Example of raw time history of thrust and torque without bubble and with bubble by 2 blowers in full load condition Fig. 4 Example of raw time history of the local shear force (acting on the sensing plate) when five blowers were active From the thrust identity analysis using measured thrust and the propeller open characteristics measured in NMRI, the effective mean velocity at propeller plane is estimated. Figure 7 shows the ratio of resistance and effective wake fraction between with and without bubble. As showed in this figure, with the appearance of bubble, ratio of resistance decreased opposite with the increasing tendency of ratio of effective wake fraction. It means the mean flow in the propeller plane increases due to the skin friction reduction. Figs. 5~6 show two examples of thrust and torque measurement in two cases: ballast condition and full load condition. As shown in these figures, torque and thrust are decreased due to the effect of bubble and similar time delay can be observed due to the distance between the injection point and the propeller. The value of thrust deduction can be assumed constant with and without bubble, because the main cause of thrust deduction is the upstream pressure drop by producing the thrust. So, in this case the total resistance seems to be reduced about 10% in Fig. 5 and about 5% in Fig. 6. The total resistance reduction of the ship is about 11% and 6% in case of ballast condition and full load condition, respectively. 1.2 R/R0, (1-w)/(1-w)0 1.1 In experiment, number of revolution was fixed, so the torque reduction means the power reduction. It means that the fuel consumption should be reduced by this reduction. 1 0.9 0.8 0.7 R/R0 (1-w)/(1-w)0 0.6 0.5 0 1 2 3 4 5 6 Number of blower Fig. 7 Analyzed ratio of R and 1-w between with and without bubble for ballast condition, pitch angle 16.9 degree Propeller pitch 16 degree, ship speed 13.1 and 13.2kt Total resistance consists of 30% wave making resistance and 70% viscous resistance based on full scale prediction from model experiment. The ship which was used in full-scale experiment has large bottom area and this area is nearly 50% of wetted surface area in ballast condition. The effect of bubble was only observed at the bottom of ship. It means that 11% total resistance reduction obtained in experiment is the reduction in viscous resistance of bottom part. From the above analysis, if we consider only bottom area of ship, the viscous resistance reduction of covered area by bubbles will be 35%. From Fig. 7, if resistance is reduced 11%, nearly 12% of increase of 1-w is observed. The ratio of resistance and 1-w is shown for one condition in table 2. Fig. 5 Example of raw time history of thrust and torque without bubble and with bubble by 5 blowers in ballast condition 90 dθ 7 υ 14 ) = 0.0225( dx 72 θU Table 2. Values of 1-w, 1-t and total resistance rate when 5 blowers were active and propeller pitch angle was set 16.9 degree. Total resistance ratio Viscous resistance ratio of bottom area 1-w 1-t (assumed constant from model exp.) Without bubble 1 1 With bubble 0.89 0.65 0.573 0.81 0.638 0.81 This is the well known relation and the non-dimensional form is as following. The over bar ̄ represents the non-dimensional value. 1 − dθ 7 14 − 14 = 0.0225( ) θ = a ( Rnθ ) 4 72 Rn dx where From table 2, 1-w is increased by 0.65. The viscous wake wv is estimated from ITTC procedure (wv = w-wp = w-(t+0.04), wv: viscous wake component, wp: invisid wake component, 0.04: rudder effect). If wv for with bubble condition is estimated using wv is proportional to viscous resistance of bottom viscous resistance because the propeller plane flow almost comes from the bottom area, predicted 1-w is 0.642. This value is a little bit higher than the measured value, but the increase of mean velocity can be explained by the resistance decrease in bottom area considering that the density change and details of the flow field were ignored. a = 0.0225( 4 ν : Reynolds number 1 ⎛ 5 ⎞5 − C f = 2a ⎜ a ⎟ Rn 5 x ⎝4 ⎠ (7) 1 − 1 5 (8) When bubbles were injected, due to the effect of bubbles, frictional coefficient will be smaller. Assume that we can express the relation between Cf (local frictional coefficient with bubble) and Cf0 (local frictional coefficient without bubbles for same momentum thickness Reynolds number) like the equation below: We assume velocity distribution in boundary layer by using the 1/7 power law like in Eq. 1 ⎛ Uθ ⎞ C f = k (ta , void fraction distribution)C f 0 ⎜ ⎟ ⎝ υ ⎠ 1 (1) (9) In Eq. 9, ta is air layer thickness. The value of ta is expressed as follow. And using the following local skin friction law 1 UL Using Eq. 2 with the value of momentum thickness received from Eq. 7, we obtain The simple integral method for two dimensional boundary layer is employed to consider the phenomena obtained in the full scale experiment. For without bubble conditions, the following equation is well known as the simple method (Schlichting, 1979). ⎛ υ ⎞4 τ = 0.0225ρU ⎜ ⎟ ⎝δ ⎠ Rn = ⎛ 5 ⎞5 − θ ( x) = ⎜ a x ⎟ Rn 5 ⎝4 ⎠ 4 7 4 7 14 ) 72 (6) After solving the above equation, momentum thickness will be represented as CONSIDERATION USING SIMPLE INTEGRAL METHOD u ⎛ y ⎞7 =⎜ ⎟ U ⎝δ ⎠ (5) ta = 1 τ ⎛ υ ⎞4 Cf = = 2i0.0225 ⎜ ⎟ 1 ⎝ δU ⎠ ρU 2 2 (2) Qa ( BaU ) (10) where, Qa is injected air flow rate, Ba is the width of the injection plate. Therefore B Where δ: boundary layer thickness, U: the uniform flow velocity L: ship length, θ : momentum thickness y: the distance from the surface, ρ: the density τ: shear stress, Cf: local skin friction coefficient υ: kinematic viscosity δ u U 0 θ =∫ ⎛ u ⎜1 − ⎝ U 7 ⎞ ⎟dy = δ 72 ⎠ 1 1 − − dθ 1 = kC f 0 = kaRn 4 θ 4 dx 2 To the point x = x0 (injected point), we obtain the momentum thickness using original Eq. 7. So, the momentum thickness at x0 is shown as follows (3) The momentum integral equation is shown as the following. dθ τ = dx ρU 2 (11) 5 5 4 − 1 θ ( x0 ) 4 = aRn 4 x0 (4) (12) Momentum thickness at initial value of x = x0 must be the same in case of bubbles and without bubbles. So, we can obtain the momentum thickness for with bubble condition as follows Where x : the distance from the leading edge in flow direction So the momentum thickness will be obtained as follow 91 5 − 5 4 1 5 4 − 1 position x0 and k. In full scale experiment, bubbles were injected at 26 m downstream from the bow. In other words, injected bubble location is about 20% from the bow when it is compared with the length of real ship. From this and the above mentioned analysis, as shown in Fig 9, in case x0 = 0.2, k = 0.5 total frictional resistant coefficient reduction between with and without bubbles is 35%. This value shows a good agreement with the aforementioned result obtained in full scale experiment. 5 θ 4 ( x) = kaRn 4 x − kaRn 4 x0 + θ 4 ( x0 ) After transformation, this equation become 4 1 − ⎛5 ⎞5 θ ( x) = ⎜ aRn 4 k x + (1 − k ) x0 ⎟ ⎝4 ⎠ ( ) (13) From Eq. 13 the value of local frictional coefficient will be obtained as follow: − ⎛5 C f = 2akRn ⎜ aRn ⎝4 1 − 4 1 − 4 ⎞ ( k x + (1 − k ) x ) ⎟ 0 Figure 10 displays the momentum thickness for k=0.5 along with without bubble condition at different air injection positions. The solid curve depicted the momentum thickness without bubble. At the injection points x0 = 0.2 and x0 = 0.4 momentum thickness changed to dash curve and dash dot curve, respectively. Boundary layer development will change due to the local skin friction reduction. This phenomenon could be used to explain the increasing tendency of 1-w when bubble takes effect at the bottom of ship. 1 5 (14) ⎠ In case k = 1/2 , Eq. 14 can be rewritten as follow: − 1 − ⎛5 ⎞ C f = aRn ⎜ aRn 4 x + x0 ⎟ ⎝8 ⎠ − ( 1 4 ) 1 5 (15) The calculated value is decided by the value without bubbles and shown in Fig. 8. The Cf00 is the value for without bubble condition. Although we assume the constant k=0.5, the value of Cf/Cf00 is increasing towards the downstream from the injection point. This tendency is similar as the results obtained in NMRI using 50 m model with end plates (Kodama et al., 2007). x0=1 x0=0.2 x0=(0:1) x0=0 Cf/Cf00 k Fig. 9 CF/CF0 at different x0 k= 0.5, x0= 0.2 θ .Rn 1 5 x Fig. 8 Cf/Cf00 at k = 0.5, x0 = 0.2 Total frictional resistance coefficient is shown as follows CF = R 1 ρU 2 L 2 = θ (1) L k=0.5 1 1 R = ∫ τ dx = ρU 2 L ∫ C f d x 2 0 0 (16) Where R: total frictional resistance So, the value of frictional coefficient can be obtained by Eq. 7 and Eq. 13 for without and with bubble conditions, respectively. Fig. 10 Momentum thickness at different x0 Fig. 9 shows the relation among the ratio of total frictional resistant coefficient between with and without bubbles CF/CF0, injected bubble 92 CONCLUSIONS REFERENCES The effect of bubbles in reducing frictional resistance or ship resistance is clearly proved by full scale experiment result. The mean velocity at propeller plane is increased due to the viscous resistance reduction from the thrust measurement results. It seems the cause of the small speed gain against the large resistance reduction. The torque reduction is also observed and the required power reduction is shown. The phenomena are considered using very simple boundary layer theory. But the mechanism of frictional resistance reduction by bubbles is complicated. It is necessary to have further research to elucidate this problem. Hylarides. “Thrust Measurement by Strain Gauge without the Influence of Torque” Shipping World and Shipbuilder, Dec. 1974, pp. 1259-1260 Kodama, Y, Takahashi, T, Makino, M., Hori, T, Kawashima, H, Ueda, T, Suzuki, T, Toda, Y, Yamashita, K (2005). “microbubbles – a large scale model experiment and a new full-scale experiment” Proceedings of the 5th Osaka colloquium, pp. 62-66. Kodama, Y, Hinatsu, M, Kawashima, H, Hori, T, Makino, M, Ohnawa, M, Takeshi, H, Sakoda, M, Kawashima, H, Maeda, M(2007). “A progress report of a research project on drag reduction by air bubbles for ships” 6th International conference on multiphase flow, ICMF 2007. Kodama, Y et al. (2008). “A full-scale air lubrication experiment using a large cement carrier for energy saving-result and analysis”, Conference proceedings, the Japan Society of Naval Architects and Ocean Engineers, pp. 163-166 (in Japanese) Nagamatsu, T et al (2002). “A Full-scale Experiment on Microbubbles for Skin Friction Reduction Using ”SEIUN MARU” - Part 2: The Full-scale Experiment-”, Journal of the Society of Naval Architects of Japan, No. 192. ACKNOWLEDGEMENTS This study is sponsored by NEDO and done as the cooperative research project with NMRI, Azuma Shipping Co. Ltd., Hokkaido University and University of Tokyo. The authors appreciate of those supports. The authors would like to express the special thanks to Dr. Yoshiaki Kodama and Munehiko Hinatsu for the guidance of the project. The special thanks are extended to the crew members of Pacific Seagull. Schlichting, H. (1979). “Boundary layer theory-seventh edition” McGraw – Hill, pp. 636-639 Toda, Y, Suzuki, T, Yuda, N, Lee, Y.S(2005). “Shear stress sensor for full-scale experiment” Proceedings of the 5th Osaka colloquium, pp. 67-75. 93 International Symposium on Marine Engineering (ISME) 2009, BEXCO, Busan, Oct. 2009 Frictional Resistance Reduction using Lower Frictional Paint N.Yamamori 1, Y. Toda 2, Y. Yano 3 1. Nippon Paint Marine Coating Co, Ltd., 19-17 Ikedanakamachi, Neyagawa City, Osaka572-8501, Japan, [email protected] 2. Osaka University, Department of Naval Architecture and Ocean Engineering 2-1 Yamadaoka, Suita City, Osaka 565-0871, Japan, [email protected] 3. Kobe University, Training Ship Fukae Maru, 5-1-1 Fukaeminamimachi, Higashinadaku, Kobe City, Hyogo 658-0022, Japan, [email protected] Corresponding author Y. Toda Abstract The effect of paint coating on hull surface to the ship frictional resistance is studied. The frictional resistance acting on the newly developed anti-fouling Lower Frictional paint (LFC-AF) is compared with that on the conventional Self Polishing Copolymer (SPC) through rotational cylinder tests, towing tank experiment. The viscous resistance reduction using LFC was observed in those experiments. The results show the promising results. So, the full scale experiment and full scale monitoring during actual service voyages were conducted and the lower fuel consumption was obtained for the condition with LFC surface. This paint seems to reduce the roughness effect in the water. Keyword: Ship Resistance, Lower Friction Paint, Surface Roughness, Towing tank Experiment 1. Introduction Energy-saving technology is studied in various fields with the pressure from environmental protection and the unpredictable fuel price. In the field of ship building and operation, the energysaving by reducing the ship resistance or high efficiency propulsion system have been investigated by many researchers, for example, the group discussion 3 in 25th ITTC[1]. In this study, the Lower Frictional paint (LFC) on ship surface is studied through rotational cylinder test, towing tank experiment, full scale experiment and full scale monitoring during actual service voyages. The paint is developed by Nippon Paint Marine Coating Co. Ltd. to get the lower frictional resistance than the conventional Self Polishing Copolymer(SPC). In the rotational circular cylinder tests, LFC surface shows 5% lower frictional resistance than the conventional SPC for around 100μm. In the towing tank experiment, three same geometry ship models which have different surface condition were tested. Two of them were painted with new LFC and Self-polishing paint (SPC), respectively. These two model have similar roughness(150μm). The remaining one was not painted and the FRP surface was polished to make the surface smooth (very low roughness). The resistance tests and velocity measurement in boundary layer were conducted. From the results of resistance test, total resistance coefficient of LFC surface model was about 6% lower than that of SPC surface model where fluid number was 0.25 to 0.4. And viscous resistance coefficient of LFC model was about 10% lower than that of SPC model where Reynolds number was 3.5 million to 5.5 million. From the velocity measurement, the axial velocity component in the boundary layer around new paint surface was larger than that around SPC surface. Therefore, roughness effect of LFC should be smaller than that of actual roughness. The simple consideration using White’s equation was done based on the measured results. In result, roughness effect of LFC on geometrical roughness of 153μm was 94 N. Yamamori, Y. Toda and Y. Yano equivalent to that of 50μm. The full scale performance was estimated using equivalent roughness. The LFC seems to have the potential to reduce fuel by 5 % for 150μm roughness. The results of monitoring for actual ships and full scale experiment of ship resistance are also presented and the results show very promising feature. 2. Laboratory Experiment In the laboratory, the rotating cylinder test and resistance test using 3m model were carried out. The measurement of roughness was made by non-contact type roughness meter using laser displacement meter. The roughness of test cylinder surface was measured directly by special device. The roughness of the model surface was measured by measuring the replica surface taken from the model surface. 2.1 Rotating circular cylinder test To measure the difference of frictional resistance acting in the paint surface, the rotational cylinder testing device was used to select the good paint. It is similar as the device used in Tanaka and Toda et. al[2] and the size of the cylinder is different and the devices have the similarity. The cylinder size is 10cm diameter and 10cm height. It was rotating in the 30cm diameter cylinder tank. The side surfaces of the cylinders were painted by several paints and top and bottom surfaces were treated as smooth surface. Before the tests using paint surfaces, the cylinders that have the artificial roughness similar as sand roughness were tested and the device was checked. The results show the test device can show the change of frictional resistance due to roughness. The measurement device is shown Fig.1. The torque acting on the rotating cylinder was measured by subtracting the torque acting on the shaft and by the support bearings using the test without a cylinder (shaft only). The examples of results are shown in Fig.2. In the figure, the torque is nondimensionalized using surface velocity and side surface area as shown in Eq.(1) and plotted versus Reynolds number Rn based on the circumferential length and surface velocity. Ct means frictional resistance coefficient or local skin friction coefficient. Ct Torque 1 D 2 nD D 2 2 2 Torque Rn 1 2 n 2 D 5 4 n 2 D 2 (1) where n: number of revolution of cylinder per second D:Diameter of circular cylinder :density : kinematic viscosity 0.0070 0.0065 0.0060 従来型 1 SPC1 従来型2 SPC2 従来型3 SPC3 LFC1 LFC2 LFC3 従来型4 SPC4 Ct 0.0055 0.0050 0.0045 0.0040 0.0035 0.0030 1 Fig.1 Experimental device for rotating cylinder. 6 11 16 21 26 31 36 41 46 [x10 5] Fig.2 Example of test results. Re In Fig.2, frictional resistance with several LFC surface are compared with frictional resistance with conventional SPC surface. Those surfaces have similar surface roughness around 90-100 m . Although those surface have the similar roughness, frictional resistance acting on the LFC surface clearly lower than that on SPC surface for all surface speed range. The frictional resistance acting on the smooth surface finished by buffing is lower than those results. To investigate the paint surface effect on the frictional resistance, the frictional resistance increase from smooth surface to paint surface is shown in Fig.3 at Rn=4,000,000 for LFC and SPC surface with various roughness. 95 N. Yamamori, Y. Toda and Y. Yano Fig.3 frictional resistance increase due to paint surface versus surface roughness As shown in figure, the frictional resistance of LFC group is lower than that of SPC group. Usual paint surface using usual painting device is 100-150 m , so LFC surface frictional resistance seems to be lower around 5% than usual SPC surface. LFC surface seems to reduce the effect of roughness. 2.2 Towing tank experiment To measure the effect to the frictional resistance in the developing boundary layer due to painted surface, usual resistance tests using 3 m mathematical models were conducted in Osaka University towing tank (length: 100m, width: 8m, depth: 4.35m). The model geometry is shown by Eq.(2). y B z 1 2 d 2 2 x 2 1 L L 3.0m B 0.5m d 0.2m where x : distance from midship in lengthwise direction y : distance from center plane in lateral direction z : distance from still water plane in depthwise direction (2) The three FRP models were made from same mold and geometry of the models were checked before painting. The conventional SPC and present LFC chosen by rotating cylinder tests were painted on two model surface by same painting procedure, respectively. The roughness of conventional SPC surface and LFC surface were 160 m and 153 m , respectively. The other model surface was finished by buffing to the hydrodynamically smooth surface (the roughness 11 m ). The surface roughness was the mean of the measured values on the replica surfaces taken from several model surface points. The photographs of the model are shown in Fig.4. After painting, the models were dipped into artificial seawater for three weeks and tested. Four resistance tests were conducted every one month and the painted models were dipped between the tests. Before the fresh water towing tank test, then models were washed by water. The test results for four tests were very similar, so the final test result is shown in this paper. As shown in top photographs, no turbulence stimulation device was installed on the model. The resistance test was conducted using usual two yawing guides, dynamometer (100N full scale) and towing rod as shown in the bottom photographs. The displacement weight (bare hull weight +ballast weight) of the models was kept to same value (1,306N) during experiment. The carriage speed U was changed from 0.4m/sec to 2.4m/sec. The example of resistance test result is shown in Fig.5. Fig.5(a) shows the measured resistance and (b) shows the total resistance coefficient. The resistance coefficient curve shows the laminar effect at low Froude number (Fn) and usual curve which has the large wave making resistance at high Fn. The resistance increase of the painted surface from the smooth surface due to the roughness is observed in the figure. But, the increase is clearly different between SPC surface and LFC surface. From the comparison between two painted surface, even in (a), the clear resistance reduction for LFC surface model from conventional SPC model resistance is observed in high speed range. From Fig.5 (b), the resistance reduction due to LFC paint compared with the model of SPC paint is seen in all speed range. The reduction is 4-5%. Although two painted models have similar roughness on their surface, the resistance of LFC model increases only 3-4% on the contrary that of SPC model is 8-10%. 96 N. Yamamori, Y. Toda and Y. Yano Fig.4 Models for towing tank experiment and resistance test apparatus (a) (b) CT R 1 U 2 S 2 Fn U Lg R :Total resistance (N) L: Model length(m) S :Wetted surface area(m 2 ) :Water density(Kg/m3 ) g :gravity acceleration(m/sec 2 ) Fig.5 Results of resistance tests To investigate the effect of paint surface to viscous resistance, usual analysis of resistance test was done for hydrodynamically smooth surface model. Form factor K is estimated as 1.11 from low Fn data. Wave making resistance coefficient was estimated by subtracting viscous resistance (1+K)CF0 from CT total resistance coefficient. Frictional resistance coefficient CF0 of equivalent flat plate is calculated by Schonherr equation. For painted models, the viscous resistance coefficient is estimated by subtracting wave making resistance at same Fn from total resistance coefficient due to the same geometry. Fig.5 shows the total and resistance coeeficient for three models along with frictional resistance coefficient of the equivalent flat plate and wave making resistance. The viscous resistance coefficient of the painted models is larger than the smooth model due to roughness. R UL Rn 1 U 2 S 2 R :Total resistance (N) L: Model length(m) CT CF 0 0.242 log10 ( RnCF 0 ) S :Wetted surface area(m 2 ) :Water density(Kg/m3 ) : kinematic vis cos ity (m 2 /sec) K : Form Factor CT ( smooth) (1 K )CF 0 CW ( Fn ) (a) CV ( smooth) (1 K )CF 0 ( K :determined at low Fn ) (b) CV (SPC or LFC) CT (SPC or LFC) CW ( Fn ) Fig.5 Resistance coefficient and ratio of resistance coefficient versus Reynolds number 97 N. Yamamori, Y. Toda and Y. Yano The increase due to roughness on painted surface is smaller for LFC than for conventional SPC and the viscous resistance for LFC is smaller than for SPC. The ratio of resistance coefficient is also shown in Fig.5. From Fig.5(b), viscous resistance for LFC is lower around 10% than for SPC around Rn =3.5 to 5.5 million. The ratio of viscous resistance between two models increases as Rn increases, while the ratio of total resistance shows similar value for all Rn due to the ratio of viscous resistance and wave making resistance. From these results, LFC seems to have low equivalent hydrodynamic roughness. To investigate this effect, the simple consideration using White’s equation [3] was done based on the measured results. In the equation, equivalent roughness height k is used. Frictional resistance coefficient increase CF 0 of equivalent flat plate for a certain k was obtained by the total frictional resistance coefficient calculated by same equation (k=0) from the total resistance coefficient calculated for a certain k. Viscous resistance of painted model was estimated by adding CF 0 to viscous resistance of smooth model. The result is shown in Fig.6. Fig. 6 Prediction by White equation Fig.7 Full scale prediction Fig.8 Boundary layer profiles As shown if Fig.6, the prediction using k=160 m agrees well with experiment for SPC, on the contrary the prediction using k=50 m agrees well with that for LFC. It means that LFC has the effect to reduce the roughness effect. In result, roughness effect of LFC on geometrical roughness of 153μm was equivalent to that of 50μm. The full scale viscous resistance for ship length 50 to 300m was predicted by assuming equivalent roughness 160 m and 50 m for SPC and LFC, respectively. The ship speed was assumed 15kt. Note that k/L decreases as ship length increases due to the constant k. Result is shown in Fig.7. Viscous resistance can be reduced by using LFC instead of SPC in case of painted rough surface(around 150 m roughness). If viscous resistance and wave making resistance are similar, the total resistance can be reduced about 5%. The reduction rate depends on hull form and Froude number (the ratio of wave making resistance and viscous resistance). The boundary layer measurement at 95% length position(x/L=0.95) was conducted for three models. The velocity profile shows that the velocity in boundary layer for LFC is higher than that for SPC. It also show that LFC reduce the roughness effect and momentum loss. 3. Deceleration test using training ship ‘Fukae Maru’ To investigate the effect of paint on the full scale ship, deceleration test using the training ship ‘Fukae Maru’ of Kobe University was conducted in 2006 and 2007 after docking. In 2006, LFC was painted on the former paint and conventional SPC was painted in 2007 in similar way. So, the roughness was similar for both experiments. The test was conducted for similar draft and inside the breakwater of Kobe port to minimize the wave, wind and tidal current effect as shown in Fig.9. The four tests were carried out for following wind, head wind, port side beam wind and starboard side beam wind case. CPP propeller is installed on the ship, so the experiment was done as following. The steady speed was accomplished at S/B Full Ahead Engine(CPP blade pitch angle 20degree) around 10knot for some 98 N. Yamamori, Y. Toda and Y. Yano period and the pitch angle was changed to Stop Engine condition(pitch angle -1degree). After this change, the ship speed and position were recorded. Stop Engine condition means that the propeller does not produce the thrust at zero advance speed, so the propeller produce the drag force approximately proportional to U2. If the total resistance acting on hull is assumed to be constant around some speed, the total drag force including propeller and hull is proportional to U2. So, if the viscous resistance coefficient is smaller around 8kt, the period for deceleration from 8kt to 6kt is longer and the distance is longer. The example of ship speed time history is shown in Fig.10. From these time histories, the coefficient related to drag force is calculated by using the data between 8kt and 6kt and compared for two paint conditions. If this coefficient a is smaller, the drag force is smaller. Fig. 9 Example of experimental route Fig.10 Example of ship speed time history Table 1 shows the analyzed coefficient a. The averaged values of a for LFC(No.4-10) and SPC(No.1116) are 12.017 and 12.650, respectively. It means the total resistance of LFC surface is 5% lower than that of SPC surface. By monitoring the real operation from docking to docking for some Ferry and PCC, the fuel consumption per mile or hour was reduced by LFC. From those results, LFC seems to reduce the fuel consumption about 5% by reducing the roughness effect. Table 1 analyzed coefficient related to drag 4. Conclusion The viscous resistance of newly developed anti-fouling Lower Frictional paint (LFC-AF) was investigated through rotational cylinder test, towing tank model experiment, full scale experiment and full scale fuel consumption monitoring. In the laboratory experiment, the viscous resistance of LFCAF is clearly lower than that of conventional Self Polishing Copolymer (SPC). LFC seems to have the effect to reduce the roughness effect of real geometrical roughness. In the full scale tests, the results shows LFC paint is very promising. References [1] Hubregtse A.(Chaiman), “Group Discussion 3: Global Warming and impact on ITTC Activities”, Proc. of 25th ITTC, Vol.III, Fukuoka, Japan (2009). [2] Tanaka H., Toda Y. Higo K. Yamashita K ., “Influence of Surface Properties of Coatings to Frictional Resistance”, Journal of Kansai Soc. Nav. Archi., Japan, No.239(2003) . [3] White F. M., “Viscous Fluid Flow : 2nd Edition”, McGraw-Hill, (1991). 99 資料3 親水性ペンキによる 摩擦抵抗 減 摩擦抵抗低減に関する一考察 す 考察 大阪大学 戸田保幸、眞田有吾、植原靖子 今回のものは委員会での話の中で出てきた部分的に高性能塗 料を利用する等のことに対して検討したものであり、簡単な検 討を行った手始めで論文にまとめるほどのものではないと思わ れるが1考察としてお話させていただく • ISME2009のYamamori,Toda,Yanoの結果がベースでるのでそ れを少し見ていただいた後今回の説明をさせていただく。 100 1 Ship Models Wigley船 L=3000mm B=500mm d=200mm 排水量 33 3k f 排水量=133.3kgf 図1 Plain (無塗装船) 図2 LFCN30 (親水性塗料) 図3 LFC46(自己研磨型塗料) 図2 LFC46表面状態 (粗度 160μm) 図1 LFCN30表面状態 (粗度 153μm) 粗度の影響を計算式で表すために、レプリカで計測された10点平均 粗度の影響を計算式で表すため 、 リカで計測された 点平均 粗度高さRzを用いた。等価砂粗度との関係はこの程度の平均波長 の場合1/2の高さの砂粗度となる。 101 2 実験時の摩擦抵抗推定法 山盛らではWhiteの近似式を用いて推定されてい た。 今回はこれを直接運動量積分式を解くことによって 高価な塗料を塗る位置などについても検討。より複 雑な境界層内速度分布に対しても簡単に拡張可能 (たとえば勝井らの摩擦抵抗式を求めた速度分布な ど) 今回のアプローチ ①摩擦抵抗係数CFを、近似式ではなく運動量積 分式を直接解いてもとめる 分式を直接解いてもとめる。 ②実船で考えた場合、親水性塗料にどれほど省 エネルギ 効果があるのかを調べるとともに エネルギー効果があるのかを調べるとともに 一部に用いた場合の効果などについても検討 102 3 粗度を考慮した平板周りの境界層 d 1 cf dx U 2 2 運動量積分式 運動量厚さの定義 u u (1 )dy U U 0 乱流境界層内の速度分布 u 1 u* y u ln( ) 5.5 ΔB : U u* * U 2 粗度関数ΔB ①Whiteの式 B 1 ln(1 0.3 0 3k ) k u *k ②CebeciらのNikuradseの粗度を考慮した式 k <2.25 B 0 2.25 k <90 B ( B 8.5 90 k B ( B 8.5 1 103 1 ln k ) sin(0.4258(ln k 0.811)) ln k ) 4 u u (1 ) dy U U 1 1 1 (1 ln )( ln )d 0 ln ( ln ) 2 d 0 2 ( 2 2 ) U 1 u* 1 ) 5.5 ln(1 0.3k ) ln( * u * U u 1 u 1 u* y ln( ) ln( ) u* 1 ln y 0 1 1 ln( u 1 u* y ln 1 U U 1 y 1 ln : u u* ln( u* U e e B ' 5.5 - B 1 B ') e e B ' B ' 1 ) ( u* * U ) B' u * e e B ' 1 ( 2 2) subroutine bibun(y,f,U) y: momentum thickness θ non-dimensional f:dθ/dx nondimensional real k,Rn,c,L,U,m k=0.4 c=0.0001 L=300. am 1.11 am=1.11 z0=0.02 Rn=(U*L*1.e6)/am do i=1,50 B=5.5-1/k*log(1+0.3*Rn*c/L*z0) z=k/(log(Rn*y/exp(-k*B)/(1/k-2*z0/k*k)) zsa=abs(z-z0) if(zsa.lt.1.e-12) then go to 200 else z0=z endif end do 200 continue f=z0*z0 return end 104 5 Rougness function ΔB 14 12 ΔB 10 ΔB 8 ΔB=ln(1+0.3k)/κ 6 4 2 0 ‐2 0 100 200 300 400 k+ k <2.25 B 0 2.25 k <90 B ( B 8.5 90 k B ( B 8.5 1 1 ln k ) sin(0.4258(ln k 0.811)) ln k ) Momentum thickness L=3m L 3m 0 004 0.004 0.0003 0.002 0.0002 0.001 0 0 k=160μm k=50μm plain 運動量厚さ θ 運動量厚さ θ k=160μm k=50μm plain 0.003 L=200m L 200m 0 0004 0.0004 0.0001 1 2 Rn 0 0 3 [10 ] U 1.0(m / s ) 1.11*106 CF 1 2 Rn 6 3 4 [107] 2 CF : Frictional Resistance Coeffi L 105 6 Frictional Resistance 摩擦 擦抵抗係数CF -6 10 0* -6 84 10 =3 0* -6 *k 0 0 U =32 0*1 -06 *k 6 1 U =25 20* -06 *k 19 1-6 U k= 00*10 * U =12 0* -6 0 *k 0 0 U k=1 0*1-6 * 0 0 U k=8 *1 -6 * 0 U =60 * 1 0 *k 0 U =4 0 *k U 0.003 k/L=1.0*10-6 0.002 -6 k/L=0.5*10 -6 6 k/L=0.25*10 0.001 7 10 108 plain 109 Rn 実験の摩擦抵抗と計算値の比較 6 3 10 CF 5 103ΔCF0 4 Cv (plain) 実験値Cv (k=160μm) 実験値Cv (k=153μm) (k 153 ) 計算値 CF(k=160μm) 計算値 CF(k=50μm) 計算値 CF(plain) 3 2 1 0 1 2 3 4 Rn×10-6 5 ΔCF0 (k=160μm) ΔCF0 ((k=153μm) μ ) ΔCF0 (k=160μm) ΔCF0 (k=50μm) ただし、L=3m,動粘性係数 1.109256*106 U=0.4~2.4(m/s) 106 7 速度ごとの実船の摩擦抵抗推定値 0.003 摩擦抵抗係 係数 CF 摩擦抵抗 抗係数 CF 0.003 U=8.0knot 0.0025 0.002 0.0015 0 002 0.002 0.0015 0.001 0.0005 50 U=12knot 0.0025 0.001 50 100 150 200 250 300 350 400 100 150 200 250 300 350 400 船長 L(m) U=16.0knot 0.0025 U=24.0knot 0.0025 0.002 0.0015 0.001 50 船長 L(m) 0.003 摩擦抵抗係数 C CF 摩擦抵抗係数 CF 0.003 0.002 0.0015 100 150 200 250 300 船長 L(m) 350 0.001 50 400 k=50,80,120,160,200μm 100 150 200 250 300 350 400 船長 L(m) 親水性塗料による摩擦抵抗値減少率 16.00 実船レベルでのCF減少率 14.00 CF減少率(%) 12.00 10.00 U=8.0(knot) U=12.0(knot) 8.00 U=16.0(knot) 6.00 U=20.0(knot) U=24 0(knot) U=24.0(knot) 4 00 4.00 2.00 0.00 50 150 250 350 450 船長L(m) 107 8 cf L=3m 0 01 0.01 L=200m 0 006 0.006 局部 部的摩擦抵抗係数 cff 局部 部的摩擦抵抗係数 cff 局部摩擦抵抗係数 k=160μm k=50μm plain 0.005 0.008 0.004 0.006 0.003 0.004 0.002 0 4 10 0.002 k=160μm k=50μm plain 105 0.001 106 0 6 10 107 Ux/ν 107 108 Ux/ν U 1.0(m / s ) 1.11*106 1.40E+00 摩擦抵 抵抗係数 CF 1.20E+00 1.00E+00 8.00E‐01 6.00E‐01 4.00E‐01 2.00E‐01 0.00E+00 1 ①plain ②ks=50(μm) 2 3 ③ks=160(μm) 108 4 ④f:ks=50(μm) b:ks=160(μm) 5 ⑤f:ks=160(μm) b:ks=50(μm) 9 ③k=160 ⑤back k=50 ④front k=50 ②k=50 ①plain 運動量厚さ θ 0.001 0.0008 0.0006 0.0004 0 0002 0.0002 0 0 0.2 0.4 0.6 0.8 1 x ③k=160 ⑨中央k=50 ⑥両端k=50 ⑧後方2/3 k=50 ⑦前方2/3 k=50 ②k=50 ①plain 運 運動量厚さ θ 0.001 0.0005 局部摩擦抵抗 抗係数 cf 0 0 0.2 0.4 0.6 0.8 1 0.0025 0.002 0.0015 0 0.2 0.4 0.6 0.8 1 ③k=160 ⑨中央k=50 ⑥両端k=50 ⑧後方2/3 k=50 ⑦前方2/3 k=50 ②k=50 ①plain x 109 10 ただしこれは平板での検討で あるので船尾付近のガース長 さの減少や逆圧力勾配による 境界層の厚くなる部分では異 なると思われる。これについて は粗度関数への圧力勾配影 響も加味して積分型解法で検 討予定 塗料の部分使用 摩擦抵抗が小さいと考えられる塗料の塗り方による違いは 、塗布領域以上の効果は見込めなかった。 摩擦が高い前半部に塗るのも後半部に塗るのも摩擦抵抗 に違いはないという計算結果になった。 現在模型を5mとし検討中(次ページ) 110 11 1. 初めに 5m数式模型船を用いて水槽実験により塗膜の抵抗特性を求めた。塗膜はかなり表面粗 度が大きいものをつくり模型船における計測でも大きな差が出るものを作成し調査したも 塗装模型船を用いた水槽実験。 のである。 2. 5m の FRP 模型船を多数作成し、その表面をさまざまな粗度で塗装した(粗度12,3,4) 模型船 4 隻を用意し抵抗試験を行った。これに加え表面が滑面である無塗装模型船も実験 した。また無塗装、粗度 1 と 2 については、抵抗の差と速度分布や乱れ度の大きさの変化 の差を比較するためステレオ PIV 装置による流場計測も行ったが委員会では省略する。ま た粗度1と2については表面粗度計を試作し表面形状の計測を行い、実際の幾何粗度計測 も行った。また、抵抗から等価砂祖度を推定し、実船推定の方法を提案した。以下それら について示す。また PIV 試験用に黒色に塗装した。 2.1模型船 5000mm ま伸ばした垂直舷側 喫水より上部は喫水の形をそのま z : 水面からの深さ L : 全長 x:長さ方向距離船体中心より B z 2x y (1 ( )2 )(1 ( )2 ) d L 2 y : 各点の幅 B : 全幅 d : 喫水 模型船は表 1 に示す主要目を持つ Wigley 船型で船型を表す数式は表に入れている 全長 600mm 表 1 模型船主要目 全幅 399.8kgf 300mm 排水量 400mm 喫水 全深さ 模型船の写真を図1、図2に示す。図1が無塗装滑面模型船であり、PIV 計測のため船尾 部分を艶消しブラックで薄く塗装し研磨して滑面とした。図2は今回作成した塗装表面を 持つ模型船の一例である。塗装模型船は全体の写真は同じように見えるので表面の写真を 図3に示す。 図1 滑面模型船 抵抗試験 (a) 概要 2.2 図3 各塗装模型船の表面 図2 塗装模型船の一例 大阪大学船舶海洋試験水槽(長水槽)において、抵抗試験を表2のような日程と水温の下で 実施した。模型船は外形は完全に仕上げられているが、FRP の厚み等が異なるため模型船 重量は異なる。そのため抵抗試験に必要な治具を取り付けたのち重量を測定し、排水量が 同じになるようにバラスト重量を調整した。また船体に引いた喫水線によりトリムの調整 表 2 実験条件 使用した模型船 PLAIN船 LFC(粗度大) LFC(粗度小),LFC(粗度中) SPC(粗度中) 水温(℃) 23.4 23.4 23.2 23.2 は行った。トリム、シンケージのみフリーとしたので重心高さは厳密に調整していない。 実施日 9.12 9.13 9.14 9.15 111 が粗い。見た目の粗度の大きいほどこの場合では抵抗が大きい。 図に示すように明らかに粗度の影響が表れていることがわかる。粗度は番号が少ないほう それを模型船中央にピン接続し、各種船速(0.4m/s~2.8m/s まで 0.2m/s 毎)で曳航し、模型 す。 抵抗を無次元化し全抵抗係数で示したものを図7に示す。図中の PLAIN は滑面模型船を示 図 4、図 5 に示すように斜航軸(曳航ロッド)に検力計(型式:LMC-3502-20)を取り付け、 船抵抗(全抵抗値:Rt)を計測した。その際に、模型船が斜航、ロールをしないように模型船 図 5 斜航軸(曳航ロッド) る。これは理論的な考察から得られるものと 高速になるほど境界層が薄くなるため粗度の影響が出やすく差が大きくなる様子が見られ 抗試験解析より得られた造波抵抗係数を示す。粘性抵抗にすると同じ模型船租度であれば、 め全体の粘性抵抗傾向を見るために使用する。図8に粘性抵抗係数と滑面模型船の通常抵 塗装面での粘性抵抗を求めた。これは計測値の引き算が入るためばらつきが大きくなるた が同じであるので造波抵抗を各フルード数で全抵抗からさし引くことにより、それぞれの (低速で造波抵抗を0と仮定することにより0.05が得られた)と造波抵抗を求め、船型 さの順に変化している。次に滑面模型船で通常の抵抗試験解析をおこない、形状影響係数 の全抵抗の差がありかなり大きな差が生じている。抵抗は滑面より目視による粗度の大き 全抵抗係数にするとより粗度による抵抗変化が顕著に見える。滑面とは粗度1で約12% 図7 全抵抗係数 の前後端付近にガイドを挿入した。 図 4 抵抗試験の様子 抵抗試験結果 計測した全抵抗値 Rt を図6に示す。横軸をフルード数、縦軸を全抵抗値 Rt とする。 (b)実験結果 図6 112 図8 粘性抵抗係数 等しい傾向であるのでこの図から等価砂祖度を算出する。 (c)砂粗度による粗度関数を仮定した計算との比較による等価砂粗度の算定 2 f : 壁 面 せ ん 断 応 力 , : 流 体 の 密 度 1 c 2 運動量積分式は二次元の圧力勾配のない平板周りの流れを考えると運動量積分式は以下 のようになる. w d U dx :運動量厚さ, w U :一 様 流 速 , c : 局 所 摩 擦 抵 抗 係 数 f ここで,運動量厚さの定義は u u 1 dy U 0 U u : 主 流 方 向 の 流 速 , : 境 界 層 厚 さ これを x=0 つまり平板全縁で運動量厚さθが 0 となる条件で積分すると, x x 0 w dx 1 CF x 2 1 U 2 x 2 2 CF : 平板摩擦抵抗係数 となる.運動量厚さθを定義する乱流境界層内の速度分布がわかれば,平板摩擦抵抗係数 CF を算定することができる. 平板の乱流境界層内速度分布に対して粗度の影響を考慮した乱流境界層内の速度分布を次 式で表わす. u 1 u* y ln 5.5 B u* 0.41 : カ ル マ ン 定 数 y : 平板表面から法線方向の距離 u * ( / ) : 摩 擦 速 度, w : 動粘性係数, u *k ここで, B は粗度関数とよばれ,粗度の影響を含む項である.今回は White の式を 1 ln(1 0.3 k ) k 用いた.White の式を以下に示す. B k : 砂粗度高さ これらを用いて、模型船の抵抗試験範囲のスピードに対し等価平板の摩擦抵抗曲線を計算 した。これをさまざまな等価砂粗度に対して示したものが図9である。図9でも実験結果 の粘性抵抗と同様の傾向を示している。ただしこの計算により得られる滑面の摩擦抵抗係 CV ( k ) と表わすこと 数は若干シェーンヘルの式と値が異なるため粗度面と滑面の差をシェーンヘルに加えたも のを各粗度の摩擦抵抗係数としている。 以下,粗度 k(μm)の摩擦抵抗係数,粘性抵抗係数をそれぞれ C F ( k ) , にする. C F ( k ) のグラフを以下に示す.粗度を 0μm から 200μm まで変化させて計算し 113 た. 図9摩擦抵抗係数 CF (k ) 計算結果 図9の摩擦抵抗係数と形状影響係数を用い粘性抵抗を推定したものが、計算の粘性抵抗で それを作っておき実験をプロットし全体で傾向の合ように等価砂祖度を推定した。推定の ために実験値をのせたものを図 10 に、推定した等価砂粗度による粘性抵抗計算値と実験を 図10に示す。 図 10 作成した図9に実験の粘性抵抗を表示したもの 図 10:実験値と等価砂粗度の曲線の比較 114 される.この計算結果と実験結果の比較により,水中では LFC 粗度1が 100μm,粗度2 このように全体の傾向が一致するように等価粗度を決めることで,細かい実験誤差は除去 図 12 に今回試作した装置を示す。これにより実船塗膜なども計測可能と考えられるが、そ た計測装置を試作した。 粗度1、2について粗度を計測した。このためにレーザー距離計とトラバース速度を用い 2.3 粗度計測 が 50μm,粗度3が 25μm,粗度4が 10μm の砂粗度と等価であることが確認できた. 表3 粗度計測結果 粗度を計測すれば等価砂祖度を推定できる可能性もある。 膜面でも実粗度の約半分の高さの等価砂粗度が得られており同じような塗装面であれば実 表3に示す。等価砂祖度の比率とほぼ同じように得られており相関がある。また以前の塗 子を図16に示す。得られた結果を図 17,18 に示す。これを用いて粗度を算出したものを 船首付近、船体中央付近、船尾付近の三点で船の深さ方向に変位測定を行った。計測の様 1000μs に設定した。水槽実験を行った模型船の内、粗度1と粗度22隻についてそれぞれ 計測はレーザの移動速度を 2.0mm/s,移動距離を 50.0mm,データのサンプリング周期を 図 12 面粗度計測装置 れによるデータベース蓄積と公表は委員会では否定的であった。 この等価砂粗度を用いて実船の抵抗を推定する方法を考察する. 船の長さをさまざまに変えて同じフルード数で計算した、摩擦抵抗曲線を図 11 に示す。 これによると実船で差がある粗度であれば模型船でも差があること、また模型の計測精度 が高いことを考えれば実船で有意な差が生じる表面粗度の影響は 5m 程度の模型船で十分 同じフルード数で試験することが可能であるとみることもできる。したがって今回のよう な数式船型で数多くの塗装面に対して等価砂祖度を得ておけばその粗面に対する実船の摩 擦抵抗、あるいは粘性抵抗が推定可能である。通常の滑面模型船で通常の模型試験を行い 形状影響係数 K と各フルード数での造波抵抗係数がわかれば、図 11 の対応する塗装面で対 応する長さの船の摩擦抵抗曲線を(1+K)倍し、それに造波抵抗を足すのが 1 つの方法で あるが、これまでの相関との関係から、デザインスピードでのこれまで使用してきた塗膜 さまざまな船長に対する摩擦抵抗曲線 と新しい塗膜のΔCF の差を図 11 から推定し通常の推定結果にそれをたしひきする方法も 考えられる。 図11 115 (a) 船首面粗度計測の様子 図13 計測 (b) 船体中央付近面粗度計測の様子 得られた全データを最小二乗法で三次多項式に近似し、求めた曲線と各データの最短距離 Zp5th Zv4th Zp3th Zv2th lr Zp1th=Rp Zv1th=Rv 面粗度の基本パラメータ Zp2th Zv5th Zp4th Zv3th 図17 0.25 0.2 0.15 0.1 0.05 0 -0.05 -0.1 図18 20 X 30 表面形状計測結果 10 表面形状計測結果 50 LFC 粗度大 40 LFC 粗度中 116 を船体表面粗度として算出した。得られた船体表面粗度から(6. 1),(6. 2)でそれぞれ定義され る最大高さ粗さ、十点平均粗さを求めた。 RZ : 最大高さ粗さ V 基準長さにおける輪郭曲線の 山高さの最大値と谷深さの最大値との和 P R R R Z R ZJIS : 十点平均粗さ 1 5 ( Z PJ ZVJ ) 5 j 1 粗さ曲線で最高の山頂から高い順に 5番目までの山高さの平均と, 最深の谷底から深い順に 5番目までの谷深さの平均の和 R ZJIS ROUGHNESS, zero 0 0 100 1 0 .9 0 .8 0 .7 0 .6 0 .5 0 .4 0 .3 0 .2 0 .1 0 Vx 100 境界層でも差が出ていたので概略を示す。粗度1、粗度2、PLAIN であればこの順に協会 0 y 層の厚さが大きい。乱れ強度もこの順に大きい。 -1 0 0 -5 0 -1 0 0 -1 5 0 -2 0 0 -2 5 0 -3 0 0 -3 5 0 y 図 30Plain 32×32pixel 解析 -1 0 0 Vx -2 0 0 -200 -1 0 0 -100 0.8 0.7 y 0 -5 0 -1 0 0 -1 5 0 -2 0 0 -2 5 0 -3 0 0 -3 5 0 0.6 0.6 0 0 y 0 0.3 -50 0.5 -100 0.3 0.5 0.3 0.7 0.6 0.4 -150 0.6 0.7 0.7 -200 0.8 0.4 0.4 0.5 1 0.7 0.6 0.9 1 -250 1 0.3 0.8 0.8 0.9 0.9 1 1 1 0.9 100 1 0 .9 0 .8 0 .7 0 .6 0 .5 0 .4 0 .3 0 .2 0 .1 0 Vx 100 図32:粗度232×32pixel 解析結果 0.9 0.9 0.8 1 0 .9 0 .8 0 .7 0 .6 0 .5 0 .4 0 .3 0 .2 0 .1 0 -300 1 -350 0.9 図33:3隻の比較(赤:粗度1,青:粗度2,黒:PLAIN) 1 0.4 0 -5 0 -1 0 0 -1 5 0 -2 0 0 -2 5 0 -3 0 0 -3 5 0 粗度132×32pixel 解析結果 0.5 0.6 0.5 0.6 0.9 0.4 117 z z 1 -2 0 0 -2 0 0 図30 0.8 z z 資料5 深江丸を用いての推力トルク計測 3.1概要 通常船舶では馬力は計測される場合が多いが、推力は計測されることは少ない。プロペ ラ作動時の船体抵抗とプロペラ推力は釣り合うので、推力を計測すれば推力減少率の変化 が小さいと考えれば船体抵抗の増減がわかり、馬力はそのほかの影響、たとえばプロペラ 汚損による効率の低下(同じスラストを出すために必要なトルクの増加)が入っているた め、それらを分離して船体の抵抗の変化のみを計測できる。したがって推力を計測するこ とは大きな意味を持つ。計測手法は軸にゲージを張り付ける資料1の方法である。 3.2計測器の概要 神戸大学海事科学部の練習船深江丸がドックにおいて新しい塗料を塗装する前に深江丸 の中間シャフト(直径 145mm)にゲージを張り付けスラストトルクを計測した。装置の概 要図 36 に示す。図に示すようにシャフトに直接ゲージを張り、その出力をテレメータで送 信している。シャフト温度等も計測し温度の影響も考慮している図 37 に受信機側の表示を 示す。 図36 シャフト直貼りによるスラストトルク計測装置概要 図37 受信機とデータ取得用パソコン 118 3.3 計測結果 回転数 305rpm、可変ピッチ翼角 12,14,16,18 度において速力とスラストトルクの関係 を求めた。速度は深江丸の計測機によるものである。図 38 に推力、トルクの時系列を示す。 馬力 (PS) 推力 (ton) 時間(分) 図38 推力馬力の時系列 同じ翼角で 2 回とっているが安定しており、速度が増加するときは、速度が上がる前は翼 角が大きくなると推力、馬力とも先に一度大きくなっていることがわかる。これなスピー ドが小さく前進率が小さい部分で回っているためで、翼角を落とすときは逆の現象がみら れる。この平均値を横軸に船速を取り書いたものが推力の図 39 と馬力の図40である。 119 スラスト (ton) 船速(Kt) 図39 船速(kt)とスラスト(ton)の関係 同じ船速で見ると推力は下がっており、新しい塗料を塗った直後は大きく抵抗が下がって いることがわかる。しかし同じ翼角では推力が同じで船速が大きくなった結果が出ている。 これは J の大きいところで同じ推力を出せることを意味し、揚力特性がよくなっているこ とがわかる。これはプロペラの汚損による影響であると思われる。船速と馬力の関係を見 ると推力よりも大きく減少しており、プロペラの効率改善が大きいことがわかる。ドック 前には非常にプロペラが汚損していたものと思われる。 馬力(PS) 船速(Kt) 図40 船速と馬力(PS)の関係 120 Proceedings of 26th ITTC – Volume I 419 Specialist Committee on Surface Treatment 1. Membership Introduction 1. 2. 3. 4. Review state of the art of different surface treatment methods Review the possible impact on ship performance in the following areas in the light of the recent rapid development of coating systems: a.) Resistance (friction line) b.) Propeller characteristics c.) Cavitation behavior d.) Comfort (propeller induced noise) e.) Acoustic signature Review the existing measurement methods for surface roughness at model-scale and at full-scale Propose methods that take into account surface roughness and other relevant characteristics of coating systems in model testing. a.) Check the need for changes to the existing extrapolation laws b.) Study the roughness allowance for high-speed and conventional ships (hull, appendages and propellers) Final report and recommendations to the 26th ITTC 1.1. Meetings R. Anzböck, VMB, Austria, (Chairman) M. Leer-Andersen, SSPA, Sweden, (Secretary) M. Atlar, Newcastle University, UK J. H. Jang, Samsung HI, Korea, H. Kai, Yokohama National University, Japan E. Carillo, CEHIPAR, Spain M. Donnelly, NSWCCD, USA, left the committee on 29-01-2010 1.2. Tasks The committee met 4 times: November 24, 25, 2008, Vienna May 11, 12, 2009, Madrid February 1, 2, 2010, Daejeon October 28,29, 2010, Gothenburg 1.3. Below we list the tasks given to the committee by the 25th ITTC Specialist Committee on Surface Treatment 420 Fouling: Self cleaning from 8knots. Silicon polymers form a hydrogel microlayer between the paint surface and the seawater, resulting in enhanced antifouling capability, and improved self-cleaning potential. Service inter: 90months Toxicity: low toxicity, biocide free (VOC=Volatile organic compound) TASK 1: REVIEW STATE OF THE ART OF DIFFERENT SURFACE TREATMENT METHODS The committee found practically no support from paint manufacturers; except brochures where they claim reduction of fuel consumption up to 10 % neither reliable measurements nor serious data were provided by the industry. In the following a short overview over the products of several paint manufacturers given and a few essential comments are added to the single products. Hempel: Hempasil X3 Type: Silicone Hydrogel, low surface energy Friction: Hempel does not claim reduction in frictional resistance per se, but claims reduced resistance due to less fouling. They claim 4-8% fuel savings (see XXXXXX). Tested at Force towing tank, plates of about 1m2. Have not obtained test report. 121 Proceedings of 26th ITTC – Volume I HEMPASIL 77500 Type: Silicone, water repellent low surface tension, second generation Toxicity: biocide free Fouling: Self cleaning above 8knots Service inter: 40months 421 Friction: As seen below they claim big improvements in power, however underlying data must be investigated if possible. They claim AHR of 20micron compared to 125-150 for convetional Friction: self smoothing, exists in low (deep sea) and high polishing (coastal) Friction: self smoothing, exists in low (deep sea) and high polishing (coastal) Fouling: self polishing toxic anti fouling self smoothing Service inter:? Friction: self smoothing, exists in low (deep seae) and high polishing (coastal) Figure1:Comparedtoselfpolishingantifouling Anti-fouling nanocapsule, Cuprous oxide and other GLOBIC NCT Type: Toxicity: biosides fibres, fibres, Fouling: self polishing toxic anti fouling self smoothing Service inter:60months OLYMPIC Type: Anti-fouling mineral high mechanical strength Toxicity: Low level of VOC (400g/litres) OCEANIC Type: Anti-fouling mineral medium mechanical strength Toxicity: Fouling: Service inter:36month fouling OCEANIC Very good Fair 60 10-30knot Very good 430g/litre Zinc carboxylate Medium OLYMPIC good Neutral 36 10-25knot good 450g/litre Natural rasin Fair The following graphs, which are copies of the manufacturer’s brochure, show, what “International” claims for their products “Intersleak 700” and “Intersleak 900”. They promise a reduction of the friction coefficient of 38% without any proof; nevertheless a fuel reduction of 6% is guaranteed ignoring the type of ship, the Froude numbers and the ratio of frictional resistance to total resistance. claims better efficiency parameter (wave length). With below method claiming 38% lower Cf than intersleek 700 Friction: Claims 4% fuel savings compared to traditional SPC. Average AHR 100 Service inter:36month GLOBAL NCT Excellent High 60 0-35knot Excellent 400g/litre Nanocapsule High Specialist Committee on Surface Treatment 422 Hempasil Exellent Exellent +60 >13kn None 275g/litre Silicon None Comparison of Hempel paints Mechanical Fuel saving Drydock inter Speed Self polishing VOC Binder Biocide efficiency elastomer INTERNATIONAL INTERSLEEK 700 Type: Silicone release, self cleaning Toxicity: None Fouling: Speed: 15-30knots INTERSLEEK 900 Type: Fluropolymer fouling release, self cleaning Toxicity: None Fouling: Hydrophobic waterreppelent surface, 40% lower barnacle shear adhesion strength than intersleek 700. Better slime repellent Speed: >10knots Service inter:36month Friction: Claims 6% fuel savings compared to intersleek 700. Average AHR 75 (Intersleek 700 AHR=100, typical SPC(Self Polishing copolymer)=125micron. Also 122 Proceedings of 26th ITTC – Volume I INTERSWIFT 655 Type: Self polishing copolymer (SPC) Toxicity: Copper Acrylate biocide release INTERSMOOTH 746 Type: Self polishing copolymer (SPC), lower solvent emission Toxicity: Copper Acrylate biocide release INTERSHIELD 163 INERTA 160 Type: Anti-corrosive, Ice resistant, no ice adhesion, high mechanical strength, low temperature Toxicity: Low VOC (40g/litre) Fouling: Biocide release Service inter:36month Friction: No info found Fouling: Biocide release Service inter:up to 60month Friction: No info found 423 Fouling: No anti fouling normally Service inter:No information found Friction: Claims 7-10% fuel saving compared to traditional ani corrosive paint. Specialist Committee on Surface Treatment 424 Comparisons between International paints Data taken from http://www.international-marine.com/Literature/HRPC_Folder_Paper.pdf ”Hull roughness calculator” Figure2:Savings 123 Proceedings of 26th ITTC – Volume I Fouling: Service inter:>60month Friction: No information found 425 Figure3:Fuelincreaseusage(hybrid=mixofCDPandSPC(Interswift),CDP=ControlledDepletionPolymer(Interspeed),SPC=Self polishingcopolymer(Intersmooth),Foulrelease(Intersleek)).Allfigureshavesamedescription? JOTUN Very little information found SEALION Type: Foul release Silicone elastomer Toxicity: Fouling: Service inter: Friction: SeaQuantum Type: Self smoothing and self polishing (SPC) Hydrolising Toxicity: Specialist Committee on Surface Treatment 426 Paintsfordifferentapplicationareas Figure1:Typicalpaintsystemsfordifferentapplication Typesoffouling Severalthousandspeciesofmarineorganismscanfoulthesurfaceofaship.Mostwillstayattachor releasewhentheshipspeedisabove45knots.Whichorganismscanattachisaffectedbymany factorssuchaspH,temperature,salinity,dissolvedsaltsandoxygenconcentration. Figure2:MainMarinefoulingorgasms Typeofantifoulingpaintsinsecondhalfof20thcentury Allthoughthesepaintshavebeenlargelyphasedoutsomewherestilluseduntil2001whereIMObannedthe useofTBTpaintsworldwide,becauseoftheirtoxiceffectsonmarinelife. 124 Proceedings of 26th ITTC – Volume I Specialist Committee on Surface Treatment order to take surface roughness effect into account. In order to determine the velocity shift function by surface roughness, experiment using long pipe in which the wall can be roughened is taken place. Full scale skin friction calculated by “SHIPFLOW” is shown in Fig.14. We can not see any reliable experiment data in this paper. 428 TASK 2: REVIEW THE POSSIBLE IMPACT ON SHIP PERFORMANCE IN THE FOLLOWING AREAS IN THE LIGHT OF THE RECENT RAPID DEVELOPMENT OF COATING SYSTEMS 1. Resistance (friction line) 2. Propeller characteristics 3. Cavitation behavior 4. Comfort (propeller induced noise) 427 Task 2.1. Impact on the Resistance (friction line) In the following an overview over the recent papers concerning the impact of coating systems on the resistance of a ship is given: Lars-Erik Johansson, “The Local Effect of Hull Roughness on Skin Friction. Calculations Based on Floating Element Data and Three-dimensional Boundary Layer Theory”, Read in London at a meeting oh the Royal Institution of Naval Architects on April 11, 1984 The effect of surface roughness on skin friction is calculated. The author takes place experiment using floating element and measure both skin friction and velocity profile in boundary layer. Using those data obtained, velocity shift is determined. A boundary layer program for three-dimensional turbulent boundary layers is employed. Roughness effect upon flat plate and two ship hulls are presented. Increase in viscous resistance due to roughness from painted surface of ship is shown in Fig.14. This paper firstly shows cause of hull roughness. The effect of coating on ship performance is calculated by some formula. The effect of biocide free foul release coating to fuel saving is shown. The author concludes foul release products give lower hull roughness than biocidal AF and lower environmental impact whereas higher initial costs. 2.1.2. Ship Resistance: Resistance Data are not published Y. Yano, N. Wakabayashi : “Presumption of Bottom Fouling in Real Ship”, J. of Japan Institute of Navigation , 2008 The authors attempted to presume the degree of bottom fouling of real ship by trial test. They conducted short stopping test with conventional paint and new type paint. From experimental data, they obtained coefficient of stain. From its value, the degree of bottom fouling was assumed and the effect of paint was investigated. Friction drag by slime and shell and weed are discussed. Research history about them is shown. Methods to measure the hard paint roughness of antifouling coatings are summarized. The author refers to the relation between surface roughness and skin friction. Economic considerations are also made. Y. Yamazaki, H. Onogi, M. Nakato, Y. Himeno, I. Tanaka, T. Suzuki : “Resistance Increase due to Surface Roughness (2nd Report)”, Journal of the Five roughed plate which were obtained in hull of real ships were tested in the circulating water channel and measured frictional resistance coefficient. Speed decrease estimated by plate frictional resistance coefficient was 0.2 ~ 2 knot in case of blunt ships, and 0.3 ~ 3 knot in case of high speed ships. H. Doi, O. Kikuchi : “Frictional Resistance Due to Surface Roughness (1st Report) Effect on Reducing of Ship's speed by Roughness Models –“, Journal of the Kansai Society of Naval Architects, Japan, No.194 , 1984 Leer-Andersen M, Larsson L, “An experimental/numerical approach for evaluating skin friction on full-scale ships with surface roughness”, J. of Marine Science and Technology Vol. 8, No1, 2003 J. Willsher : “The Effect of Biocide Free Foul Release Systems on Vessel Performance”, SHIP EFFENCY, 1st International Conference, Hamburg, October 8-9 , 2001 Townsin RL : “The ship hull fouling penalty”, International Congress on Marine Corrosion and Fouling No11, San Diego, California , 2003 The authors evaluate the increased skin friction of full-scale ships by surface roughness. CFD code “SHIPFLOW” is modified and velocity shift function is used in Speed trial data of training ship during past 8 years are shown. Variations of Ship speed, shaft horse power, fuel consumption are shown in order to estimate the effect of bottom fouling. The results show shaft horse power increases about 20% in full speed condition because of fouling. Trial data are analyzed and variations of friction resistance are also shown. We can see the shaft-horse power and fuel consumption versus days after dock with self-polish. K. Yokoi, “On the Influence of Ship's Bottom Fouling upon Speed Performance”, Toyama National College of Maritime Technology, Bulletin of Toyama National College of Maritime Technology in Japan2004 decreases about 10% due to propeller polishing. We can see the increase of resistance(%) to days for developments. 2.1.1. Ship resistance: Resistance Data are published M. P. Schultz, “Effects of coating roughness and biofouling on ship resistance and powering”, Biofouling, 2007, Vol. 23, No.5, pp.331-341 Increased resistance of full-scale ship by surface roughness is calculated in some roughness conditions. Calculation methods are based on model ship resistance results and boundary layer similarity law analysis. The calculation results show increased resistance in heavy calcareous fouling is up to 86%. Values of shaft power of full-scale ship obtained by trial data are given and compared to calculation results. Both results agree well with each other. The resistance coefficient Ct of typical naval ship is shown in Fig.1. However, the data in this figure is NOT so reliable. T Munk, M Sc, “Fuel Conservation through Managing Hull Resistance”, Motor ship Propulsion Conference, Copenhagen April 26th, 2006 In this paper, variations of increased resistance of some actual ships in service are shown. The data shows clearly the effect of dry-dock and propeller polishing. One example shows increase of resistance decreases over 20% thanks to dry-docking. Another example shows increase of resistance 125 Proceedings of 26th ITTC – Volume I Society of Naval Architects of Japan, No.153 , 1984 Since hydrodynamic characteristics of sand roughened surface and painted surface were different in previous report, the author investigated this problem experimentally using simple wavy roughened surfaces. Frictional resistance and velocity distribution in boundary layer were measured in wavy surfaces. Roughness functions were obtained by experimental results. Y. Yamazaki, H. Onogi, M. Nakato, Y. Himeno, I. Tanaka, T. Suzuki : “Resistance Increase due to Surface Roughness (1st Report)”, Journal of the Society of Naval Architects of Japan, No..155 , 1983 The authors conducted experiments using roughened pipes in order to measure frictional resistance and velocity distribution in boundary layer. Relation between roughness height measured by BSRA analyzer and equivalent sand roughness was obtained. Velocity shift by surface roughness is used in order to get resistance increase. K. Tokunaga, E. Baba :” Approximate Calculation of Ship Frictional Resistance Increase due to Surface Roughness”, Journal of the Society of Naval Architects of Japan · No.152 , 1982 In order to calculate frictional resistance of a ship by surface roughness, the authors applied a-two dimensional turbulent boundary 2.1.3. Resistance of Flat Plates M. Candries, M. Atlar : “Experimental Investigation of the Turbulent Boundary Layer of Surfaces Coated With Marine Antifoulings”, 2005 Velocity distributions on turbulent boundary layers on flat plates coated with two 429 layer theory for rough surface to potential streamlines over the hull surface. Potential streamlines were calculated by Hess-Smith method. Increased resistance in full-scale ship was calculated. M. Sone : “Influence of the Fouled Ship Bottom on the Propulsion Horsepower of the Seikan Ferry-boats”, J. of the Marine Engineering Society in Japan, Vol.16, No.2 , 1981 Variations of Propulsion horsepower and fuel consumption of Seikan-Ferry boats were investigated in 10 years using measurement and abstract log-book data. This ship is docked every year and annual increase in delivered horse power due to the ship bottom fouling is about 8%. Since the paint was changed from higher-toxic one to lower toxic one, increase of propulsion horsepower seems to become higher. H. Orido, M. Kakinuma : “Speed Decrease Due to Hull Surface Roughness (in Japanese)”, Bulletin of the Society of Naval Architects of Japan · Vol.616 , 1980 The authors showed practical analysis using data of some ships in service. Relation between surface roughness and ship age was shown. Empirical approximate formula was also shown in the graph and compared with measured data. However, the accuracy of analysis seemed not to be high since the theory was not established enough. different new generation marine antifouling paints were measured. The two paints were Foul Release paint and Tin-free SPC respectively. Smooth flat plate and plate covered with sand grit were also used in order to make sure the performance of two new paints. Remarkable point is that LDV Specialist Committee on Surface Treatment 430 measurements for marine coatings have been published in the open literature. M. P. Schultz : “Frictional resistance of antifouling coating systems”, Journal of fluids engineering, vol. 126, No.6, 2004 resistance of 6.3 m long plate coated with Foul Release coating was 1.4% lower on average than that coated with SPC. Roughness functions of two paintings were shown. Towing test is carried out on three surface conditions in order to compare drag characteristics. The surface conditions are Aluminum, SPC and Foul Release coating respectively. From the experimental results, above Reynolds number 2 * 10^7, it is shown total drag coefficient of the foul release surface was on average 1.41% lower than the SPC surface. Candries M., Atlar, M. and Anderson, C.D. :” Low-energy surfaces on high-speed craft”, Proceedings HIPER '01, Hamburg, 2001 Frictional resistance and velocity distribution on several ship hull coatings in the unfouled, fouled, ad cleaned conditions were measured. Test surface coated with silicone, ablative copper, SPC copper and SPC TBT were used. The experimental results indicated little difference in frictional resistance coefficient among the coatings in the unfouled condition, however, after 287 days of marine exposure, test surface coated with silicone showed the largest increases in frictional resistance coefficient. M. P. Schultz : “Turbulent Boundary Layers on Surfaces Covered With Filamentous Algae”, Journal of fluids engineering, Vol. 122, No.2, 2000 Turbulent boundary layers over natural marine biofilms and a smooth plate were compared. Profiles of the mean and turbulence velocity components were measured. An average increase in the skin friction coefficient was 33 to 187 % on the fouled specimens. The skin friction coefficient was found to be dependent on both biofilm thickness and shape of surface. M. P. Schultz and G. W. Swain : “The Effect of Biofilms on Turbulent Boundary Layers”, Journal of fluids engineering, Vol. 121, No.1, 1999 The effect of algae to frictional resistance was investigated. The surfaces covered with filamentous algae were prepared and put in a closed return water tunnel. A two-component LDV was used to obtain velocity distribution in turbulent boundary layer. Significant increases in the skin friction coefficient for the algae-covered surfaces were measured. M. P. Schultz :” The Relationship Between Frictional Resistance and Roughness for Surfaces Smoothed by Sanding”, Journal of Fluids Engineering, Vol.124, 2002 The effect of sanding on surface roughness was investigated. The author prepared 7 kinds of plates. One of them was not sanded and the others were sanded by different fineness. Plates were towed and frictional resistance was measured in each case. The results showed resistance increase of unsanded plate against polished one was 5% in average. Roughness function U was shown of all plates. M. Candries, M. Atlar, A. Guerrero and C.D. Anderson : “Lower frictional resistance characteristics of Foul Release systems”, Pro. of the 8th Int. Symp. on the PRADS, Vol. 1, 2001 The roughness and drag characteristics of surface painted with SPC (tin-free SelfPolishing Co-Polymer) and non-toxic Foul Release were investigated. Two plates coated with these two paints were towed in tank and drag was measured. The results showed total 126 Proceedings of 26th ITTC – Volume I 2.1.4. Resistance of Circular Cylinders S.M. Mirabedini, S. Pazoki, M. Esfandeh, M. Mohseni, Z. Akbari : “Comparison of drag characteristics of self-polishing copolymers and silicone foul release coatings: A study of wettability and surface roughness”, Progress in organic coatings, Vol. 57, No.4, 2006 Drag on some surfaces coated with some paints is measured using a smooth aluminum cylinder connected to a rotor device. Downward shift of the velocity distributions and frictional resistance coefficients for each test cylinder by Reynolds number are also measured. The drag characteristics of a surface are affected by its free energy and roughness parameters. Weinell CE, Olsen KN, Christoffersen MW, et al. : “Experimental study of drag resistance using a laboratory scale rotary set-up”, Biofouling, International Congress on Marine Corrosion and Fouling No11, San Diego, California, 2003 431 A laboratory scale rotary set-up was used to measure the drag resistance, and the surface roughness of the samples was measured. Measurements on pure paint systems and measurements on large-scale irregularities were investigated. The contribution from a modern self-polishing antifouling or silicone based fouling-release paint was negligible compared to the one from irregularities of hull of ship. Hisao TANAKA, Yasuyuki TODA, Kiyoaki HIGO, Kazuharu YAMASHITA : “Influence of Surface Properties of Coatings to Frictional Resistance”, ournal of the Kansai Society of Naval Architects, Vol.239, Japan, 2003 A. Matsuyama, T. Nishiya, T. Araki , T. Imada :” Studies on Propulsive Performance by Marine Fouling of Shiphull and Propeller”, Bulletin of the Faculty of Fisheries, Nagasaki University No.83, 2001 In order to investigate effect of surface properties of coatings to frictional resistance, experiments were carried out using a rotating cylinder type dynamometer built by the authors. Frictional resistance and velocity distribution in turbulent boundary were measured. The aging effect of paints on surface roughness was shown. M. Miyamoto :” Estimation and Evaluation of Ship Performance in Actual Seas - Review and Evaluation of Fouling, Aging Effect and Sea Condition-“, Journal of the Japan Society of Naval Architects and Ocean Engineers, Vol.4 2007 In order to investigate the effect of marine fouling on ship hull and propeller, the author analyzed the log-book data from 1990 to 1998. Shaft horse power, amount of fuel consumption, admiralty coefficient and ship speed were investigated. It was recognized that fuel consumption increases up to 22% from the value of 1990. 2.1.5. Interaction Ship and Propeller The author estimates the effect of fouling, aging effect and sea condition upon real ships. The approximate method exploited by the author is verified by comparing with measured data and data of abstract log-book. As a result, it is shown that the accuracy seems to be quantitatively practical. The approximate method could be applied to design stage. Specialist Committee on Surface Treatment N. Nakai, S. Suzuki : “On the Presumption of Bottom's Roughness with Making Use of Propeller Efficiency on CPP”, Bulletin of Kobe Marchant Ship University Vol.32, Japan, 1984 432 K. Nagatomo, H. Matsushita, E. Inui, Y. Miyoshi : “Studies on Marine Fouling of the Bottom Plates and Propeller Surface – 1”, The Journal of Shimonoseki Univ. of Fisheries, Vol.41, No.4, 1993 In order to estimate the bottom fouling of real ship, practical method was presented. The speed trial test was taken place before and after docking. Surface roughness in fouled condition was estimated by the increase of frictional resistance using Bowden formulation. The results showed after docking, surface roughness became about 6.2 mm from 145ജm in cleaned condition. The foul condition on bottom and propeller of real ship was investigated. Because of long-time mooring during August to October, fouling was progressed so much. According to speed trial, ship speed became about 70% compared to cleaned condition. The cause of speed decrease came from ship hull fouling by two-third; the rest came from propeller fouling. N. Nakai, S. Suzuki : “On the Effect for Propelling Performance in Consequence of Marine Fouling and the Practical Method of Presumption of Bottom's Roughness on FUKAE MARU before Autumnal Docking”, Bulletin of Kobe Marchant Ship University Vol.32, Japan , 1983 The increased resistance caused by adhesion of barnacle to propeller was calculated. Firstly, the situation of foul of propeller was measured. The measurement results showed barnacle adhered near trailing edge near boss. Barnacles were approximated as a half-cylinder solid and loss-horse power was calculated. The calculation results showed loss horse power was over 1%. N. Nakai, S. Suzuki : “The Effect of Marine Fouling -On the Result of Actual Experiments with the Ship Installed CPP-“, J. of Japan Institute of Navigation, 1983 Bottom and propeller fouling of real ship was investigated through one year. It was known the kind of marine fouling organisms and process of attachment. The effect of marine fouling prevention by pouring sea water with dissolved innoxious copper-ion which was supplied by the system into the dome of bow-thruster was also investigated. K. Sato, K. Inoue, E. Takeda, H. Akizawa, Y. Mine, Y. Koike, Y. Miyazaki : “Experimental Study of Prevention of Bottom and Propeller Foulings with Regard to Energy Saving of Fishing Boats”, Journal of Tokyo Univ. of Fisheries, Vol.74, No.2, 1987 In order to investigate the effect of marine antifouling paints on propulsion performance of actual ships, firstly some test plates coated with some paints were put in seawater and performance of paints was studied. Secondly, speed trial tests were taken place. Variations of BHP and surface roughness just after painting, before docking, and after docking were shown. E. Nishikawa, M. Uchida :” On Propulsion Property of FUKAE MARU Equipped CPP and its Deterioration due to Surface Fouling”, Bulletin of Kobe Marchant Ship University Vol.33, 1985 The effect of surface fouling on the propeller and ship were investigated. Trial sea data of training ship equipped with CPP were obtained just before docking and just after docking in 3 years. Performances of propulsion property with and without fouling were compared. The results showed change of propulsion performance with CPP was different from the one with FPP. 127 Proceedings of 26th ITTC – Volume I 2.1.6. Further Papers of possible Interest 2.1.6.1. Paint Elisabete Almeida, Teresa C. Diamantino, Orlando de Sousa :” Marine paints: The particular case of antifouling paints”, 2007 The authors presented a general overview of marine antifouling paints. Firstly, interaction between ship hull and sea water was explained. Marine organisms that adhere to ship hull were shown. The history of the development of antifouling technology was explained. As a next generation marine paints, more environment and man-friendly antifouling paints, such as CDPs, TF-SPCs and Biocide-free paints were shown. Chambers LD, Stokes KR, Walsh FC, et al. : “Modern approaches to marine antifouling coatings”, 2006 This article reviews the development of marine antifouling coatings. Historic antifouling methods were shown. Over 100 papers were review in it. Among them, 10 major paper were chosen and introduced. Performances of some coatings are compared. Tin-free self-polishing copolymer (SPC) and foul release technologies are current applications however many alternatives have been suggested. Casse F, Swain GW : “The development of microfouling on four commercial antifouling coatings under static and dynamic immersion”, 2006 Four test panels coated with paints were immersed in seawater in order to compare their performance against microfouling under static and dynamic immersion. Three paints were biocide based (tributylin self-polishing, copper self-polishing, copper ablative) and one was biocide free (silicone fouling release). It was know that total bacteria counts were 433 similar on all coatings after static immersion, but after dynamic immersion the largest decrease in numbers was seen on the fouling release coating. Tetsuya SENDA : “Ship Bottom Anti Fouling Coating and Marine Environment (in Japanese)”, 2006 History of development of anti-fouling coating is summarized. Since restrictions against toxic coating have become harder in recent years in terms of protection of marine environment, the author evaluates the environmental risk for anti-fouling coating. The author says it is necessary to establish the way to evaluate properly environmental effects of anti-fouling substances, and to find some low-risk substances. Anderson, C.D., Atlar, M., Candries, C., Callow, M.E., Milne, A. and Townsin, R.J : “The development of Foul Release coatings for seagoing vessels”, 2004 This paper describes the history of development of antifouling paint. Firstly, some marine fouling organisms are explained. Secondly, some explanation about antifouling painting is done. The method how fluid drag on foul-release coating is calculated is explained. Lastly, performance of antifouling coating is shown. Reading this paper, reader can get the overall knowledge of antifouling painting. Kazuya OGAWA : “The Prevention of Marine Fouling on FRP Ship Hull by Coating a Non-polluting and Anti-fouling Paint 2 Relation between Preventative Performance and Physical Properties of Silicone Coated Film-“, 1996 Specialist Committee on Surface Treatment 434 In the second report, the author investigates the reason why the proposed new coating method has an effectiveness for the prevention of bio-foulings on FRP ship hulls. The physical properties of the coated film are investigated. The author measures a contact angle and a sliding angle of a drop of water on the silicone coated film. The author also observes the repelling appearance of colored water sprayer on this film. Kazuya OGAWA : “The Prevention of Marine Fouling on FRP Ship Hull by Coating a Non-polluting and Anti-fouling Paint 1 Effectiveness of Silicone Coated Film against Marine fouling-“, 1996 In the first report, the author develops new coating method by using a nontoxic paint instead of toxic paints. FRP test plane with some coating are put in sea for several month 2.1.6.2. Marine Creature Schultz MP, Kavanagh CJ, Swain GW : “Hydrodynamic forces on barnacles: Implications on detachment from foulingrelease surfaces”, 1999 In this paper, lift and drag acting on barnacles were measured. The results were compared to the results obtained by and antifouling performance are compared with each other. The paint which shows the best antifouling performance is painted to real ship and its performance is confirmed. Nobuyoshi HIROTA : “Non-Toxic Anti Fouling Coating without Adhesion of Marine Creatures (in Japanese)”, 1985 Development and application of non-toxic anti fouling coating called “Bioclean” developed by CHUGOKU MARINE PAINTS LTD is explained. In case of the application to the propeller of the 200 thousand DW ore carrier, it is reported that no adhesion of marine creatures occurred in half year after launching. In case of the application to the propeller of the support ship of national defense ministry, it is reported that no adhesion of marine creatures occurred in one year. hemisphere, cube and pyramid. Lift coefficient remained nearly constant over the range of Reynolds numbers tested, however drag coefficient decreased slightly with increasing Reynolds number. A table of the literature checked for task 2a is attached in appendix 1 to this report. review of reasons and associated different coating methods reported in the open literature are given. Based on this review since the Foul Release (FR) coating systems have been developing as the prime propeller coating system, in 2.2.4 a brief background to this coating system is given with a view to the TASK 2.2: IMPACT OF PROPELLER COATING SYSTEMS ON PROPELLER CHARACTERISTICS 2.2.1. Introduction This section gives a background on propeller coating systems and their influence on propeller characteristics. In item 2.2.2. the important aspect of the propeller surface measurements and representation are reviewed. This is followed by 2.2.3. where the 128 Proceedings of 26th ITTC – Volume I propeller coating. Item 2.2.5. presents the recent applications and review of the effect of the FR coatings on the efficiency, cavitation and underwater acoustics of propellers as well as the interaction of this coating system with bio-fouling. Finally, 2.2.6. presents the concluding remarks from the review and recommendations for further research on propeller coating. When the loss in ship performance is associated with the condition of the ship hull, the effect of the propeller surface condition is often overlooked. Mosaad (1986) stated that in absolute terms, the effect of the propeller surface condition is less important than the hull condition, but significantly more important in terms of energy loss per unit area. In economic terms, high return of a relatively cheap investment can be obtained by propeller maintenance. This has been well recognised by cautious ship operators who regularly polish the propellers of their vessels. While this is a good practice, the inconvenience of finding suitable time and place as well as the associated cost favour for the alternative means of keeping propellers clean by coating, especially after the recent introduction of Foul Release (FR) type coating. Besides, there has always been an interest to the coating of propellers to avoid or reduce fouling growth and galvanic corrosion of ship hull and as well as to resist to cavitation erosion if it is ever possible. Propeller coating applications have been growing with increasing applications of foul release (FR) coatings on ship hulls during the last fifteen years or so, especially on the propellers of large cargo vessels. According to the data base of one of the major coating manufacturers, the current breakdown of the ship antifouling applications, about a 5% of their hull coating applications is with the FR type and this ratio has been increasing considerably due to environmental scrutiny and competitions amongst newly emerging other FR brands. This type of coating is favoured for the propeller applications due to 435 their smoother finish and improved application as well as longevity relative to the Self-Polishing Copolymer (SPC) types. In fact some paint manufacturers have been offering free of charge paint applications to ship owners who are willing to paint their vessels by FR coating. Again, according to the data base of the above mentioned major paint manufacturer the number of the coated propellers has reached to more than 250 during the last 10 years. The main objective of propeller coating is to control fouling growth beside other potential benefits in association with improved condition of the blade surfaces including propeller efficiency, cavitation and noise. However prior to exploring these effects, one needs to clarify differences amongst surface deterioration and fouling. Surface deterioration may be caused by corrosion, impingement attack, cavitation erosion or improper maintenance whilst fouling is mainly due to marine growth of the animal type, acorn barnacles and tubeworms as well as the slime type, Atlar et al (2002). Depending upon its extent while the surface deterioration can be represented by surface roughness the representation of fouling is rather complex and hence its effect upon the propeller is difficult to quantify since very little theoretical and experimental work done on the subject. However it is a well-known fact that, whether it is a surface deterioration or fouling, any micro or macro level change in the blades surfaces will increase the propeller loss due to the viscous friction effect in addition to the potential axial and rotational losses. The frictional loss can be as high as 15% of the total propeller losses depending upon the propeller’s loading condition, Glover (1991). It is therefore beneficial to keep the propeller surface free from marine fouling and as smooth as possible to reduce the frictional loss beside other consequences of these causes that may lead onto undesirable earlier inception and further development of cavitation as well as increased underwater noise. Specialist Committee on Surface Treatment 436 This was then used to calculate a value for the Average Propeller Roughness (APR). This is a weighted average, so the roughness closer to the tip has a much greater influence than the same roughness would, if placed nearer the blade root. Five sections were suggested and given the weights shown in Table 1. h ' | 0 .0147 R a2 ( 2 .5 ) PC In an attempt to establish a standard methodology for the propeller roughness measurements Townsin et al. (1985) proposed the following procedure: each blade surface is divided into a number of roughly uniform radial strips, for each of which 3 measurements were taken with a cut-off length of 2.5mm. At that time this was designed for use a stylus type roughness device, the Surtronic 3 instrument, so Ra (the mean line average roughness amplitude) and Pc (the Peak Count per unit length, which is a texture parameter) were recorded for later conversion into Musker’s “Apparent” or “Characteristic” roughness parameter, h’, by the approximation below. give a wide range of values for all roughness parameters; therefore for any point on the blade, an average of many samples is needed to reach a representative figure. However these values of average roughness will vary hugely over the blades surface, meaning that the roughness needs to be measured at many locations. This is important as the same level of roughness will cause very different effects on section drag, depending upon where on the blade it is located. Fouling and damage, such as galvanic or cavitation erosion, can have a massive effect upon the roughness measured and hence the section drag. Most importantly, there was no agreed standard methodology for measuring roughness, no matter how arbitrarily defined. 2.2.2. Measurement and representation of propeller surface condition Before the effects of roughness upon the performance of a propeller can be quantified the roughness of the surface has to be measured. There are various methods for doing this, such as using a propeller roughness comparator, by using a portable stylus instrument or by taking a replica of the surface of the blades and measuring it with laboratory equipment such as optical measurement systems. A detailed description of both the stylus (by mechanical contact with the surface) and optical measurement systems can be found in e.g. Thomas (1999). On the other hand the propeller roughness comparator is a simple gauge by which the roughness of a propeller can be compared to a surface of known roughness. The most wellknown example of this is the Rubert propeller roughness comparator. The gauge consists of six examples (A, B, C, D, E and F) of surface finish that range from an average meanline roughness amplitude Ra = 0.65μm to an amplitude of Ra = 29.9μm, see, e.g. Carlton (2008). The examples represent the surfaces of actual uncoated propeller blades. Examples A and B represent the surface roughness of new or reconditioned propeller blades while the remaining examples are replicas of surface roughness taken from propellers eroded by periods of service. C, D, E and F can be used to assess and report upon the propeller blade surface condition after periods of service. The measurement of propeller roughness, whichever method is used, presents a number of problems which are similar problems to those of measuring hull roughness. They stem from the very nature of propeller blade roughness, with its wide variety of amplitudes, textures and locations. Townsin et al (1981) discussed the propeller roughness measurement problems and concluded the following: any one small area of a blade will Table 1. Weights suggested for calculating APR, based on 5 sections. 129 Region 0.20.5 0.50.7 0.70.8 0.80.9 0.9tip Weight 0.07 0.22 0.21 0.27 0.23 3 437 fully turbulent frictional drag expression for the propeller blade surfaces in ITTC’78 procedure, will not be suitable for representing the effect of coatings on propellers. This is not only on the ground that this expression is based on the Nikuradse approach of sand roughness, since actual propeller roughness is different than the sand roughness, but also on the ground of neglecting the effect of surface texture. Although a surface may have relatively large average roughness amplitude its texture may have a long wave length sinusoidal texture. This type of surface may cause lower drag when compared to a surface consisting of smaller amplitudes but with a jagged texture consisting of closely packed sharp peaks surface as claimed by Grigson (1982). This claim was further proved by Candries (2001) through comprehensive boundary layer, drag and roughness measurements and analysis of flat plates coated with two different marine coatings which were a commercial FR and a tin free Self-Polishing Copolymer (SPC) type. In this study it was shown that the FR coated system belonged to the former surface type while the SPC coated surface belonged to the second type suggested by Grigson as typified in their comparative roughness profiles shown in Figure 1. It can be seen that when longwavelength waviness, which is unlikely to have any effect upon the drag, has been filtered out, two striking features appear: not only are the amplitude parameters (i.e. Ra, Rq, Rt) of the FR profiles typically lower, the texture parameter of the surface, which is represented by the slope (Sa), is significantly lower. In metrological terms this type of texture is known as “open” whereas the spikier texture of a tin-free SPC surface is known as “closed”. 5 10 20 25 30 35 Foul Release Roughness profile: Ra = 1.10 Rq = 1.21 Rt = 4.50 Sk = -0.87 Ku = 5.04 Sa = 0.33 15 mm 40 45 Specialist Committee on Surface Treatment 0 438 20 15 10 5 0 -5 -10 -15 2.2.3. Review of propeller coatings 50 As it is noted in the above review, an accurate representation of blades surfaces by characteristic roughness parameter requires relatively sophisticated measurement devices for proper analysis of the surfaces. These devices are preferred to be optical and portable as well as practical that can be used in dry docks etc. Unfortunately such systems currently are not available although there are increased activities in this field especially after the introduction of the FR coatings. As discussed earlier these coatings do not readily allow themselves to be measured by practical stylus type devices although they are currently being used on based on certain skills involving some errors in measurements. Although taking replica (print) from the actual blade surfaces is relatively direct and hence more accurate way measurement method, it is rather impractical and it has its 20 15 0 5 10 -5 -10 -15 0 5 10 20 25 30 35 Tin-free SPC Roughness profile: Ra = 3.26 Rq = 4.04 Rt = 19.98 Sk = 0.01 Ku = 3.29 Sa = 2.57 15 mm 40 45 50 In demonstrating the effect of fouling on propellers and its prevention by coating Kan et al (1958) investigated the characteristics of conducted in order to conserve the scarce alloys usually used for propellers. Cast steel is much cheaper than bronze, can be easier to coat and requires less exacting manufacturing technology, so was proposed as an alternative. At least 4 ships had coated steel propellers installed during the war. Three of them were sunk and unfortunately no follow-up was made on the fourth Dashnaw et al., (1980). own problems. At this point, until such devices are available, it is plausible to think of establishing a new comparator system, which is based on a similar idea to the Rubert comparator. However this new comparator can be developed for foul release coated sample surfaces which are graded based on different paint applications varying from good to bad since the application grade is an important parameter in the texture and roughness parameters for newly applied coatings. Of course these samples will be indirect and will not necessarily represent the actual coated blades after a period in service. However, as long as they are not damaged, FR coating systems can maintain they roughness and texture characteristics similar to the new condition except the effect of slime. There may be ways including this effect but requiring further research. Figure 1 – Characteristics of a typical foul release (Intersleek 700 – on the left) and tin-free SPC (Ecoloflex – on the right) roughness profiles taken by laser profilometry, Candries et al (2001). micron Proceedings of 26th ITTC – Volume I i 1 2 3 4 5 1 º ª 5 3 «¦ Wi (h'i ) » ¬1 ¼ By assuming h’ is constant within each weighting band; APR for the 5 bands is given by, APR 3 mn5 A more generalized form for APR, suitable if a survey of the entire blade roughness is not available (the missing values should not just be assumed to be zero) is given by APR 1 º ª n 3 « ¦Wi (h'i ) » « m n » « ¦m Wi ¼»» ¬« The weights are evaluated such that for a uniform distribution of roughness, APR = h’. In the above procedure “characteristic” roughness parameter h’ was obtained from a drag-roughness correlation with replicated coated surfaces based on Mosaad’s (1986) extensive measurements. This parameter was originally proposed by Musker (1977) to characterize a surface by a single parameter taking both the amplitude and texture of the roughness into account. At this point it must be noted that a single parameter (such as average roughness height) as those measured by Broersma and Tasseron (1967) or equivalent sand roughness height (ks) of the The idea of coating a marine propeller is not a new one. The first recorded idea was by Holzapel (1904) who claimed two major reasons for the coating of marine propellers, as true today, namely to prevent fouling and to reduce galvanic corrosion. Unfortunately his comments were not taken up at the time and further investigation into the concept of coating marine propellers was not conducted for some time. It was not until the second World War that further development of protective coatings for marine propellers was 130 micron figures was presented. Three coatings were proposed for further evaluation and were coated onto blades of a 6.5m bronze propeller. The two coatings were polyurethane formulations and one was an undisclosed formulation (known as Y-1). They were inspected after 2 and 11 months in service. It was found that the polyurethanes had quickly delaminated from the propeller. Y-1 had fared better. From these trials they realised that for any propeller coating, the bond strength of the adhesive/primer was of fundamental importance. They recommended that for the broad surface area of the blades, under low hydrodynamic loading, the coating needed an adhesion strength of at least 8.92 kN/m (50 lb/in.) of width. Near the edges of the blades, where the surface was under high and dynamic hydrodynamic loading, a much higher strength would be needed. Proceedings of 26th ITTC – Volume I a fouled propeller using self-propulsion tests and full-scale trials with the propeller covered in various rubber sheets to mimic the fouling. They found that small increases in roughness will cause large increases in delivered horsepower (DHP), producing a worse effect on propulsive efficiency than hull fouling but the reduction in thrust due to roughness was very small. These experiments, however, did not give very good agreement with their fullscale results. The full-scale measurements showed that the rate of increase of DHP will decrease as the roughness increases; the initial roughness has the greatest effect on performance. Because of propeller fouling, the DHP decreases by 20% and from these results, it can be seen that the effects of propeller fouling in terms of a power penalty are much greater than those of surface roughness. 439 Further work was conducted from the 50’s to the 80’s particularly focusing upon the prevention of cavitation damage e.g. by Heathcock et al. (1979), Angell et al (1979) and Akhtar (1982). These mostly used ceramic coatings and were not just interested in propellers but also, rudders, A-brackets and turbine blades. Foster (1989) described trials on 2 Canadian naval vessels that had their propellers coated with a 3-layer vinyl antifouling system that used a cuprous oxide containing topcoat. This was at the time the standard system used on the hulls of the Canadian naval fleet. The first vessel, CFAV Endeavour, found that, after 2 years in service, the coated propeller (the ship had twin screws and only was one coated) was fouling free and only had small amounts of paint loss on the leading edges of the blades. They also found that the shaft grounding current of the coated propeller was reduced to about a third of the uncoated one (the information on current demand was taken from the monthly cathodic protection reports of both ships). The second ship, the naval frigate HMCS MacKenzie had both of her propellers coated. They were examined by divers after 6 months and again in dry-dock after 2.5 years in service. The divers found that the coating was fouling free and almost intact except for some detachment along the leading edges and some small isolated spots on the back of the blades. They also noted that the coating was still red in color suggesting that little copper had leached out. Once in dry-dock, it was found Dashnaw et al. (1980) published their work studying a large number of coatings and surface finishes, in order to investigate those that might prevent cavitation damage and corrosion while still providing a smooth surface to minimise the hydrodynamic drag. Their theory being that, if a suitable covering system could be found it might be possible to replace the expensive materials propellers that are usually made from by cheaper steel. They conducted tests using a 24 inch rotating disc apparatus and found that certain urethane coatings could produce less drag than bare steel discs even with a higher value of the root-mean-squared roughness amplitude, Rq. They concluded that there was a 10% change in drag approximating to a 1% change in power at the propeller, although no explanation as to how they arrived at these Specialist Committee on Surface Treatment 440 that while still free from fouling, the damage had grown. The small isolated spots on the back of the blade, most likely caused by cavitation, had grown to a diameter of 530mm. A 30mm wide strip had been eroded along the trailing edge and the top-coat had been removed from the leading edge back to about the mid-chord. The cathodic protection reports showed that the current demand had dropped by about 30% while at rest and at sea by about 20% compared to the pre-coated condition. They maintained these figures throughout the 2.5 years in service. Coldron and Condé (1990) reported on the Shell Engineer, a 1300dwt coastal tanker, generating 905kw at 250rpm through a 4 bladed nickel-aluminum-bronze propeller, 2.44m in diameter. In 1983 it was selected to trial the effect of a TBT-SPC based coating on its propeller. This system was suggested by the wealth of published data on the coatings performance on ships hulls. The propeller was removed, faired, wet blasted and then dried before the coating system was applied. Two alternate blades were coated with a vinyl shop primer and 2 with a 2 layer epoxy primer. The whole propeller was then coated with two layers of the TBT-SPC system (an extra coating was also added to the outer half of the blades. The roughness of the propeller before and after coating can be seen in Table 2. Table 2. A comparison in the roughness of the surface both before and after painting 110.3Pm 43.7Pm 60.38% Rtm (2.5) Coldron and Conde (1990) Ra (2.5) Prior to 23.2Pm Painting 14.2Pm After Painting 38.79% % Change The propeller was inspected after both 6 and 12 weeks and was found that the TBTSPC coatings had rapidly been removed from the vinyl primer. The SPC on the epoxy performed better with only some mechanical damage to the tip. The polishing rate of the SPC was found to be very low when compared to that expected of a ship’s hull. The epoxy was slowly ‘stripped’ back along the suction side from the tip inwards so that 25% had been removed after only 3 months. In 1989, after 6 years in service, 20% of the epoxy, near the blade roots, still remained on the propeller Further trials were conducted, this time using a ceramic coating, in order to try and prevent a problem with localized but random cracking of the propellers of the Shell Marketer class of vessels Coldron and Condé (1990). Two blades were, cleaned, degreased, preheated and the grit blasted before being coated not more than 40 mins after the surface preparation. The coating used was a ceramic mix, with an alumina base, with 13% titanium added (this improves the impact resistance but reduces the electrical resistance). The coating was applied using a plasma flame spray system with argon/hydrogen plasma gas. The two remaining blades were prepared to the manufacturer’s standard finish. After a period of 4 years, the propeller was inspected to find that the coated blades had actually become smoother compared to their initial roughness after coating. The uncoated blades, however, had deteriorated to a surface about 50% rougher than their initial value. The coating had managed to remain attached, even in an area where mechanical damage had removed part of the coating, there was no evidence of ‘creep back’. Although it should be considered highly unreliable, due to the complex nature of the effect of propeller condition on ship performance, it was also noted that the Shell Marketeer was performing 6% (in terms of nautical miles per tonnes of fuel) better than its sister-ship, the Shell Seafarer, whose blades had not been 131 Proceedings of 26th ITTC – Volume I coated, but were of a similar roughness to the Shell Marketeer’s blades prior to their coating. Matsushita et al. (1993) noted that because the training ship of the Yuge National College of Maritime Technology in Japan, the Yuge-Maru, was at anchor for long periods, the propeller had a serious problem with biofouling. The seawater around its home port ranged from 8-9°C to 27-28°C, a wide variety of adhesive sea life were present in the surrounding waters, including at many different species of barnacle (such as Tintinnabulum rosa, Amphitrite tesselatus and Amphitrite hawaiiensis), Bryozoans (calcarious colonial animals, similar to corals), Serpulids (a type of tubeworm), mussels, oysters, algae and bacterial biofilm. Therefore researchers at the college, as part of a wider investigation into the effect of a non toxic coating of silicone resin decided to coat the ship’s propeller. The coating system had been developed as an industrial, non-polluting paint in such areas as seawater suction pipes and cooling pipes of nuclear plants. Since there was no toxin present in the coating chemistry it was considered safe to the environment. The surface had similar properties to the modern Foul Release properties, with a low surface energy and high water repellence. The antifouling ability was derived from the low attachment strength of marine fouling organisms to the surface. This was then the first reported experiment with a FR coating on a marine propeller. The propeller was first cleaned and then allowed to foul over a six month period. Upon inspection after this period it was found that the propeller was heavily coated in fouling (mostly bryozoans and serpulids) particularly 441 in areas of slow flow speed over the surface e.g. the boss and blade roots. After the inspection the propeller was then re-cleaned and coated with silicone resin paint. 6 months after coating, the propeller was again inspected. The coating was found to be intact and free from fouling except for a few flat bryozoans on the root. After a further 6 months the propeller was inspected a third time, again no damage to the coating was found, there was however, some bryozoans and slime fouling present. These results were the first to show that a foul release coating can remain attached to a propeller and achieve effective antifouling in actual service. In addition to the propeller inspections described above the fuel consumption was recorded for both the un-coated and coated propellers were recorded over the course of three months during the summer fouling breeding season. It was found that the fuel consumption with the 6.2% lower when the propeller was coated although the lack of details about the change in hull condition over the trial period mean that this change cannot be attributed to the condition of the propeller alone. The Yuge-Maru also had a large number of sacrificial zinc anodes attached around the hull to protect the hull from electrochemical corrosion by galvanic action in seawater, caused by the copper alloy propeller. Each side of the ship has 23 anodes attached to the shell plating, one in the bow thruster tunnel, one on each of the upper and lower bearings of the rudder post and one at the end of the stern tube, see Figure 2. Specialist Committee on Surface Treatment 442 Within the framework of galvanic corrosion Atlar (2004) noted that some ship owners and propeller manufacturers may think that partially coated propellers, which can represent possible damage to paint or a paint failure, could be subjected to complex corrosion effect due to inherent differences in two surfaces. Although such corrosive damage has not been reported in any of the vessels with coated propellers, within the capability of modern cathodic protection systems this should not be a problem. His consultation with a major UK propeller manufacturer revealed that the final surface finish of a large propeller by hand may take about a month of time while with a machine this will take at least a half of this period. In the mean time, the application of coating on propeller surface would require relatively rough surface, which is obtained by grid blasting, to provide the coatings with a necessary grip to stick on the surface. Based upon this requirement, the propeller manufacturer does not perform the final finish, and hence save labour cost and delivery time, but this was still much lower than the current output of the uncoated disc. Although done on a small scale, this is further strong evidence that the coating will reduce the galvanic current caused by the propeller. Figure 2 - Arrangement of Sacrificial Anodes (Zn Plates) on ship body of Yuge-Maru (Matsushita et al., 1993). Table 3 shows the amount of degradation of the anodes of the course of a year without the propeller being coating and as a comparison the levels of degradation of the replacement anodes over a year once the propeller was coated. The level of deterioration was low for both cases (less than 5%); suggesting that the number of anodes attached to the ship was excessive. The results did show however, as expected, the anodes near the propeller were the most reduced (except number 3, inside the bow thruster tunnel). The difference between anode degradation in the uncoated and coated propeller condition was approximately 30% in favour of the coated propeller condition. This suggests that the propeller coating stopped or significantly reduced the galvanic current. In fact this has since been confirmed by more recent research by Anderson et al. (2003) who conducted further testing of new generation FR system, on the propellers (and replacement metal discs) of a 100th detailed scale model of a frigate, to investigate the effect of a propeller coating upon the current output of an Impressed Current Cathodic Protection (ICCP) system. They found that the use of the coating “markedly reduced” the ICCP current output. When the coating was damaged, there was an increase in the output, 132 Proceedings of 26th ITTC – Volume I while the paint manufacturer will apply grid blasting directly on this surface. This way all three parties: the owner; propeller manufacturer and paint manufacturer can benefit as well as the environment Table 3. Consumption of Sacrificial Anodes (Zn plates) of the TS Yuge-Maru. (Matsushita et al., 1993) A B C 95.4 5.2 2.2 4.0 5.5 12.6 2.2 4.0 Total A B C 95.4 5.2 2.2 4.0 3.95 4.5 8.4 6.2 Non-Propeller Coating Propeller Coating (07.03.1989-28.02.1990) (10.03.1990-04.03.1992) Zinc Anode New Zinc Rate of Zinc Zinc Anode New Zinc Rate of Zinc Position Weight Consumption Position Weight Consumption (Kg) (%) Number (Kg) (%) Number 1 3.5 2.1 1 3.5 3.1 2 3.5 2.1 2 3.5 3.6 3 3.5 14.2 3 3.5 14.9 4 3.5 3.5 4 3.5 3.0 5 3.5 2.4 5 3.5 3.4 6 3.5 2.7 6 3.5 4.3 7 3.5 3.0 7 3.5 3.6 8 3.5 3.1 8 3.5 3.9 9 3.5 3.4 9 3.5 2.7 10 3.5 2.5 10 3.5 3.1 11 3.5 2.7 11 3.5 2.5 12 3.5 2.3 12 3.5 1.9 13 3.5 1.4 13 3.5 2.2 14 3.5 1.2 14 3.5 2.6 15 3.5 1.5 15 3.5 3.1 16 3.5 3.1 16 3.5 4.3 17 3.5 4.6 17 3.5 3.9 18 3.5 2.9 18 3.5 2.9 19 3.5 8.9 19 3.5 0.4 20 3.5 9.1 20 3.5 3.1 21 3.5 2.5 21 3.5 2.1 22 3.5 6.1 22 3.5 3.0 23 3.5 9.6 23 3.5 4.7 24 3.5 13.6 24 3.5 4.9 Subtotal 84.0 4.5 Subtotal 84.0 3.65 Total = = = = Shell Plate (B-4) Upper Gudgeon Lower Gudgeon End of Stern Tube 1-24 A B C Another Japanese trial was conducted, this time using the training ship Kakuyo Maru Araki et al., (2000) and Araki et al. (2001). The ship’s 2.85m diameter propeller was coated with a silicone resin (Bioclean DX – Chugoku Marine Paint Company Ltd.). After 1 year in service, the propeller was inspected to find only light slime on the blades, with only a little paint having been removed from the tips of the blades. Improvements were also noted in the rate of fuel oil consumption, fuel oil pump index, and shaft horse power required, compared to the fouled propeller, 443 although it was unlikely that this was due to the condition of the propeller alone. Over the years propeller coatings have been tested that have a wide range of properties that effect propeller performance and durability of coating. In the search for the perfect propeller coating a number of attributes have been highlighted as desirable. Coldron and Condé (1990) defined the attributes of an ideal propeller coating as follows:x Exhibit adequate erosion, abrasion, corrosion and cavitation resistance and be resistant to impact damage and penetration. x Posses anti-fouling characteristics or be smooth to simplify removal of marine biofouling. x Retain an acceptable level of properties when exposed to seawater with low water permeability to prevent degradation of bond strength by corrosion of the coating/substrate interface. x Possess adequate bond strength initially and after prolonged seawater immersion to withstand the operating conditions, including maintenance procedures. x Be non-conducting to reduce cathodic protection current requirements by limiting the cathodic area. x The materials should be cheap, readily available, and relatively easy to apply and repair. x The coating must be capable of inspection for quality assurance purposes. x The coating must be sufficiently thin that it can be applied within the blade thickness tolerance range and not require expensive re-design of the propeller. In practice this implies a coating in the thickness range of 100 to 250μm. To the above list it can be added two further attributes, that have become more Specialist Committee on Surface Treatment 444 desirable in the years since Coldron and Condé published their list: x The coating must be as environmentally benign as possible. x Preferred to reduce any radiated signatures emanating from the propeller as much as possible (especially important for naval vessels and cruise ships). A number of possible propeller coating types have been developed that each have some of the above attributes but not all of them. The possible types were listed by Coldron and Condé (1990) as in the following Organic Coatings This is a wide ranging group of coating types that includes both current SPC technology and Foul Release antifouling coating technologies, epoxies, vinyls, neoprenes, urethanes and polyamides (nylons). There are a wide range of possible application methods such as airless spray, brush and roller. Some can even be coated onto the propeller in either a fluid or powdered state and then autoclaved to give the final coating, although such methods are hard to use for large modern merchant propellers, due to the need for an autoclave of sufficient size. Metallic Coatings A wide variety of metallic coating could be considered for marine propellers. Some may even have antifouling properties, if they contain compounds metals with known antifouling properties such as Copper, Zinc, Tin or other heavy metals. They could, in theory, be deposited a number of different methods, such as by electroplating, thermal spray, weld overlay or vapour deposition. This group could also include, laser surface melting, when a thin layer of the surface is heating to improve the surfaces resistance to cavitation, e.g. Tang et al., (2004, 2005). The development of these coating would require large scale facilities to allow merchant propeller, typically of 5-10m diameter to be treated economically. Metallic coatings also suffer from the problem of, if two dissimilar metals are in contact, a galvanic cell will form causing accelerated corrosion. This is why little research has been done on this type of coating for use on propellers. Ceramic Coatings This type of coating are created a powdered mix of mineral substances including clays and metal oxides (aluminum, chrome and titanium oxides are widely used) that are then fired (or specialist techniques, such as thermal spray processes can be used) to produce a dense, low porosity coatings. The properties vary widely, depending on what chemicals are what proportions of each chemical are used. They can be insulating or semi-conducting and the hardness can be varied. They are usually inert in seawater but not all can withstand high levels of cavitation. Expensive research into the ideal chemical formula would be needed before their use as a propeller coating will become widespread. No coating has yet been found to have all the attributes in the list, so the perfect coating is still elusive. The current leading contenders for a suitable propeller coating and their properties compared to the above requirements can be seen (not in any order of importance) in Table 4. Table 4. The four systems currently most likely to be developed as a propeller coating are the two leading types of antifouling system (silicone based foul release and copper based SPC) and metallic and ceramic type coatings. The qualities of each coating system compared to the desired attributes are shown. Those coloured green indicate that the system exhibits that attribute successfully, orange indicates that the system may exhibit that attribute or no evidence for the system displaying that attribute was available and red indicates that the attribute is not exhibited. 133 Proven antifouling ability Inert in seawater Silicone Foul Release Softer coating Proceedings of 26th ITTC – Volume I Resilience to Damage Antifouling Ability Inert in Seawater Copper SPC Hard coating Metallic Coating Hard coating Ceramic Coating Non toxic Unproven, No mechanism known Inert in seawater Hard coating Proven attachment to propellers Non conductor Strong Attachment Proven antifouling ability Leaches away with time Proven attachment to propellers Unknown, may conduct Already in production Non Conducting in Already production Proven attachment to propellers Depends upon ceramic used Development and material costs required Depends on coating used Thin coating likely Cheap to develop and produce Unproven, possible with some metals Depends upon the chemistry used Unknown attachment ability Likely to be conductor Development and material costs required Depends on coating used Thin coating likely No effect likely upon No effect likely Depends coating used 445 analysis, using a variety of diagnostic liquids, measuring the angles that the liquid droplets make with the coated surface. It is the surface tension of a polymer which is the property that has most commonly been correlated with resistance to befouling, Brady and Singer (2000). A generalised relationship between Surface Tension and the Relative amount of bio Adhesion has been established and presented in a graph commonly known as the “Baier curve”, which does not display the minimum relative bio adhesion (22~24 mN/m) at the lowest surface energy. A variety of explanations has been given to account for this including the effects of elastic modulus (E), thickness and surface chemistry of coatings as discussed by Anderson et al (2002). Elastic modulus is key factor in bio adhesion and hence ability of organisms to “release” from a coating, Brady and Singer (2000) and Berling et al (2003). The calculated Critical Free Surface Energy (c) for a range of different polymers indicated that there was a better correlation between the relative bio adhesion and (cE)1/2 than with either surface energy or elastic modulus, of the attributes when compared to the other types of coating as will be discussed further in the next. Coating easy to inspect Coating thins over time No effect likely Inspection of Coating Thickness of Coating Noise Reduction Toxic leachate to Coating easy to inspect ~350mic, 3 layer system Pliable, may reduce Noise Non toxic Harmful environment From the table it can be seen that silicone based fouling release systems displays more 2.2.4. Review of foul release coating technology Foul Release (FR) coating technology is the fore runner of the modern coating systems for ship propellers. In comparison to traditional antifouling technologies, FR technology relies on a fundamentally different concept of fouling prevention. Instead of using the slow release of a biocide into the surrounding water, FR coatings work by providing a surface to which fouling species find it difficult to attach securely, this is known to be “low free surface energy” surface. The fouling is then removed from the surface by hydrodynamic shear force. The free energy of a surface, which is commonly referred to as “surface energy” or “surface tension”, is the excess energy of the molecules on the surface compared with the molecules in the thermodynamically homogenous interior. The size of the surface energy represents the capability of the surface to interact spontaneously with other materials, Brady (1997). The surface energy and the critical surface tension of surface are determined by comprehensive contact angle Specialist Committee on Surface Treatment 446 Brady and Singer (2000). Thickness is another characteristic of low surface energy coatings that plays an important role in bio adhesion. It has been found that below ~100μm dry film thickness barnacles can “cut through” to the underlying coats and thus establish firm adhesion. Above this thickness there is no marked increase in FR properties. The majority of current FR coatings are based on the molecule Polydimethylsiloxane (PDMS) which are generally formed by a condensation mechanism. This long chain polymer has a long flexible ‘backbone’ that, along with the low intermolecular forces between the methyl groups, allows it to adopt the lowest surface energy configuration. PDMS has, in air, a surface energy of 23-35 mN/m and such lower value of surface energy and its elastic nature makes PDMS perfectly suited for use as a FR type coating, Brady and Singer (2000). In fact, for PDMS and other silicone material, J C E , was found to be at least an order of magnitude lower than that of other materials (Singer et al., 2000). It has been found that incorporation oils can enhance the FR properties of PDMS polymers, Milne (1977). Oils, by their nature, are lubricants and therefore should decrease the friction, but this is not the main reason for the efficacy of PDMS. This is thought to be due to the surface tension and hydrophobicity changes that the oils effect during the curing process and after immersion, Truby et al (2003). When Foul Release coatings were commercially introduced in the mid-1990s and applied to a high-speed catamaran ferry, replacing a toxic Controlled Depletion Polymer (CDP) antifouling, the recorded fuel consumption was lower at the same service speed, implying lower drag characteristics as reported by Millett and Anderson (1997). As a consequence a research project was set up at Newcastle University with the objective of collecting data on the drag, boundary-layer and roughness characteristics of Foul Release and tin-free SPC coatings, and to compare them systematically, Candries (2001) The coatings used were a PDMS Foul Release and a tin-free copper-pigmented acrylic SPC that contained zinc pyrithione as a booster biocide. Drag measurements were carried out in towing tank experiments with two friction planes of different size (2.5m and 6.3m long), which showed that the Foul Release system exhibits less drag than the tin-free SPC system when similarly applied. The difference in frictional resistance varied between ca. 2 and 23%, depending on the quality of application as reported by Candries et al. (2001). Rotor experiments were also carried out to measure the difference in torque between uncoated and variously coated cylinders. In addition to coatings applied by spraying, a Foul Release surface applied by rollering was included because there were indications that this type of application might affect the drag characteristics. The measurements indicated an average 3.6% difference in local frictional resistance coefficient between the sprayed Foul Release and the sprayed tin-free SPC, but the difference between the rollered Foul Release and the sprayed tin-free SPC was only 2.2%, Candries et al. (2003) The friction of a surface in fluid flow is caused by the viscous effects and turbulence production in the boundary layer close to the surface. A study of the boundary-layer characteristics of the coatings was therefore carried out in two different water tunnels using four-beam two-component Laser Doppler Velocimetry (LDV) and the coatings were applied on 1m long test sections that were fitted in a 2.1m long flat plate set-up, Candries and Atlar (2005). Velocity profiles were measured at five different streamwise locations and at five different free-stream velocities. A rollered surface and a sprayed Foul Release surface were tested to investigate the effect of application method. The measurements showed that the friction velocity for Foul Release surfaces is significantly lower than for tin-free SPC surfaces, when similarly applied. This 134 Proceedings of 26th ITTC – Volume I indicated that at the same streamwise Reynolds number the ratio of the inner layer to the outer layer is smaller for Foul Release surfaces. The inner layer is that part of the boundary layer where major turbulence (and hence drag) production occurs. Statistical analysis of the values of the roughness function obtained by means of multiple pairwise comparison, using Tukey’s test, indicated that the roughness function for Foul Release surfaces is significantly lower than for tin-free SPC surfaces at a 95% confidence level. These findings are consistent with the drag characteristics measured in the water tunnel and rotor experiments In addition to the difference in frictional resistance and the roughness function, the roughness characteristics of each of the surfaces were investigated. The average values of their roughness were measured using the BMT Hull Roughness Analyser, which is the stylus instrument in common use in dry-docks or underwater, for standardised hull roughness measurement. It measures Rt (50), which is the highest peak to lowest valley roughness height over a sampling length of 50mm. Successive values are averaged over a surface. It is clear from the rotor experiments and the large plate towing tank experiments that this single amplitude parameter does not correlate with the measured drag increase for Foul Release surfaces, as it does with SPC surfaces. A detailed non-contact roughness analysis was carried out with an optical measurement system fitted with a 3mW laser. Measurements were taken on sample plates coated alongside the surfaces tested in the towing tank and water tunnel, and were thus assumed representative of the test surface characteristics. In the case of the cylinders used in the rotor experiments, sections were cut from the cylinders after testing, for use in the optical measurements. A moving average was applied to filter long-wavelength curvature. The upper bandwidth limit or cutoff length was set at 2.5 and 5mm, whereas 447 the lower bandwidth limit or sampling interval was set at 50mm. The detailed roughness analysis revealed that when long-wavelength curvature has been filtered out, the amplitude parameters of the sprayed Foul Release surfaces are in general lower than those of the rollered Foul Release surfaces and the SPC surfaces. However, the rollered Foul Release surfaces display a roughness height distribution which is considerably more leptokurtic (i.e. exhibits a larger number of sharp roughness peaks) than the sprayed Foul Release surfaces. The greater number of high peaks on the rollered Foul Release surfaces is expected to engender higher drag than sprayed Foul Release surfaces. The main difference between the Foul Release and the tin-free SPC systems lies in the texture characteristics, as shown in Figure 3 for two typical roughness profilogram of such coatings, applied by spraying. Whereas the tin-free SPC surface displays a spiky “closed” texture, the wavy “open” texture of the Foul Release surface is characterised by a smaller proportion of short-wavelength roughness. This is particularly evident in texture parameters such as the mean absolute slope and the fractal dimension. There is relatively little data available in the literature of irregularly rough surfaces on the influence of texture only on drag. Grigson (1982) has mentioned explicitly that open textures have a beneficial effect on drag. It is clear that in order to correlate with drag, the roughness of the generality of irregularly rough surfaces needs to take both amplitude and texture parameters into account, e.g. Musker (1977) and Townsin and Dey (1990). Based on the experiments presented, it was thought that the rheology of the paint, which is significantly different for foulrelease and tin-free SPC coatings, had a direct effect on its texture, whereas amplitudes depend significantly on the application quality. A correlation analysis of the texture Specialist Committee on Surface Treatment 448 parameters with the amplitude parameters, however, has shown that the two are interrelated, so that bad application can be expected to have a knock-on effect on the texture parameters At present, the procedure adopted by the International Towing Tank Committee (ITTC) to correlate roughness with drag only accounts for a single roughness amplitude parameter, ITTC (1990). The procedure hinges on the use of a practical formula for the added ship resistance (or roughness correlation allowance), which was proposed by Townsin and Dey (1990) in terms of Average Hull Roughness for the moderately rough ship range where Rt(50) is less than Pm. Unfortunately, this procedure may not work for foul-release surfaces, unless a texture parameter is included in the roughness characterisation. For a selection of 41 different coated surfaces, including 8 newly applied foul-release surfaces, Candries and Atlar (2003) found that the measured drag correlated reasonably well best when the roughness measure, h, is characterised by h = 1/2Ra.'a where Ra is the average roughness amplitude while'a is the mean absolute slope. There was a need for further testing and correlation studies to provide further support for this correlation. Figure 3. Typical roughness profilograms taken from a tin free SPC coated surface, Ecoloflex, (above) and Foul Release, Intrersleek 700, coated surface (below) using laser profilometry, Candries and Atlar (2003) 135 Proceedings of 26th ITTC – Volume I 449 University propeller coating research, and some numerical and experimental work was conducted with the scaled model of this propeller with the following main particulars given in Table 5 and operating conditions given in Table 6. scaled service condition of the propeller) a slight drop in efficiency (2.48%) was noted. Neither of these values was large enough to say that the coating made a significant change to the propeller efficiency beyond that of experimental error. It was noted that with the coating the inception of the tip vortex cavitation appeared at approximately a 5% lower value of the rpm for the uncoated propeller, although this could easily be due to the poor application of the coating (applied by brush) or mechanical damage on the leading edges of the blades. No adverse effect of the coating to the extent of the cavitation was noted whilst the coating stayed intact until the end of these tests except small peeling off at the sharp edges, Candries et al. (1999). In addressing at the second stage investigations (2) more through and long term research was planned. This has involved numerical and experimental investigations as well as fullscale trials / observations to demonstrate if there were any benefits or disadvantages of applying FR coating on propellers in terms of propeller efficiency, effect on cavitation inception, type and extent of cavitation and underwater noise emission from propellers. The following section gives a brief review and findindgs from these investigations. 2.2.5. Foul release coating research – as applied to propellers While the earlier summarized research on the FR coatings was continuing to understand their general drag reduction mechanism, there was further interest from industry to research on the application of these coating systems on propellers in the following two areas: (1) if the FR coatings can successfully stay on yacht propellers in arduous conditions; (2) if the FR coatings can display any performance benefit for a large commercial vessel propeller that was coated with the earlier mentioned FR system, Intersleek 700 (IS700). In addressing at the first investigation area (1), a pilot experimental study was conducted with a 3bladed, 300mm diameter, aluminum alloy model of a commercial motorboat propeller. The model was coated by IS700 using a rollering technique as opposed to spraying to simulate a real life scenario for small craft owners. Open water tests were conducted in the Emerson Cavitation Tunnel of Newcastle University in atmospheric and reduced vacuum condition. In the latter case the propeller was exposed to several hours of cavitating condition to check on the adherence resilience of the FR system. In the atmospheric condition a slight increase in propeller efficiency of 0.16% was recorded. In a vacuum condition (equivalent to the 2.2.6. Effects on propeller efficiency Based upon some plausible fuel saving reports after the application of IS700 coating on the propeller of a 100,000 DWT tanker, it was decided to use the propeller of this vessel as the benchmark propeller for the Newcastle 6.85 m Deadweight Length Overall, LOA Ship type Propeller Table 5. Main particulars of the basis vessel and propeller Diameter, D 0.699 0.524 Vessel Medium sized tanker 96920 tonnes 243.28 m Pitch Ratio, P/D Expanded Blade Area Ratio, AE/A0 Max Draught, T 9893 kW 14.86 knots 13.62 m Specialist Committee on Surface Treatment 450 Speed 1992 4 Power(installed) Number of Blades, Z Year built 0.48 19.57 Right/H Design Advance Coefficient, JA Direction of rotation 4.66 0.334 Table 6. Operational conditions 10 Fully Loaded Condition 0.520 104 In consultation with a major UK propeller manufacturer, it was assumed that a roughness equivalent to Rubert A represented a degree of smoothness unlikely to be achieved in practice. Rubert B was considered characteristic of a new or well polished propeller and Rubert D to E would be equivalent to the blade roughness after 1 to 2 years in service. In the numerical analysis it was assumed that the new or polished propeller had Rubert B blade surfaces, the drag of which was represented by the design CD values taken from Burrill (1955-56). The increase in CD caused by blade roughening was then given by the difference between the ' CD values corresponding to the Rubert surface in question and that for Rubert B. The effect of the increased roughness on the drag coefficient for the section at r/R = 0.7 is shown in Table 8. The total drag coefficient was represented by the sum of the frictional drag and the form drag as in the following where t is being the thickness of the blade section: ' C D 2 (1 t / c ) ' C F 0.48 0.486 0.75, 0.70, 0.65, 0.60, 0.55, 0.50, 0.45, 0.40 100 Ballast Condition Scale ratio, O Cavitation number, V Propeller immersion, H (m) Propeller speed (RPM) Design JA J range tested ª1 º 8.1 Re 0.093 « h ' c 4.5 Re 1 / 3 » ¬3 ¼ Atlar et al (2002) conducted numerical investigations on the open water performance analysis of this propeller by using a boundary element theory based lifting surface analysis tool in which the effect of the FR coating was simulated in the appropriately selected drag coefficients of the propeller blade section. In this selection the increase in section frictional drag due to roughness was represented by the expression given by Mosaad (1986) as: 1000 'C F Where Re is the blade section Reynolds’ Number; c is the section chord length; h’ is the roughness parameter as defined by Musker described earlier. Values for h’ for the various Rubert surfaces were calculated by Mosaad and are given in Table 7. Table 7. Musker’s characteristic roughness measure of Rubert gauge surfaces. 1.32 3.4 h' ( P m) 14.8 A B Rubert Surface C 160 49.2 252 D F E 136 Proceedings of 26th ITTC – Volume I Surface 0.0083 38 Design Rubert D 0.0100 3 19.7 Rubert E 0.0113 8 35.8 Rubert F 0.0120 6 43.9 Table 8. Drag coefficients of Rubert surfaces (Design = Rubert B). CD % Increase The key decision on this analysis was the determination of characteristic roughness values (h’) for the foul release coated blade surfaces. In this decision the measurements made with the FR coated flat plates by Candries (2001) played an important role. The surface characteristics of 5 different applications were studied using a UBM Optical Measurement System from which it was found that the roughness measure h’ varied between 0.5 and 5Pm. The quality of application ranged from excellent to good, so that it was considered appropriate to assume a value of h’ = 5Pm. The calculated values were negligibly different from those calculated when using the Design CD values. From this it can be inferred that a foul release coated blade surface was equivalent to the new or well polished blade surface. Based on the above assumption the sectional drag coefficients in the numerical tool was modified and the propeller performance with the design CD values was first was calculated for varying operating (advance coefficient) conditions and this procedure was then repeated with the drag coefficients corresponding to Rubert D, E and F surfaces for the same conditions. The results of the comparisons were presented in the open water curves of this propeller as shown in Figure 4 where the predominant effect of an increase in the roughness of the propeller blades was an increase in the propeller torque. The decrease in propeller thrust that accompanies the increased torque was too small to be obvious on the figure’s scale. 451 Figure 4. Propeller open water characteristics for various values of blade surface roughness, Atlar et al (2002). The loss in propeller efficiency (KRas the propeller blades roughen, to a base J, is shown by Figure 5. Performance data for the subject vessel from which the propeller was modelled showed that on average propeller worked at a value of J = 0.48. As shown in Figure 3 the propeller efficiency losses due to blade roughening (or gains by keeping propeller clean) were about 3%, 5% and 6%for surfaces of roughness represented by Rubert D, E and F, respectively. In summary, this numerical investigation showed that significant losses in propulsive efficiency resulting from blade roughening can be regained by cleaning and polishing of the blades. Alternatively, the efficiency losses could be avoided, perhaps indefinitely, by the application of a paint system that gives a surface finish equivalent to that of a new or well-polished propeller. A foul release coating could be such a paint system. Atlar et al (2003) conducted the similar analysis, this time applied on high-speed and large surface area propellers. The simulations for the open water performance of the GawnBurrill Series based propeller of a twin-screw patrol gun boat indicated rather plausible efficiency gain (or loss) which was almost twice the maximum efficiency gain (or loss) Specialist Committee on Surface Treatment 452 obtained with the earlier reported tanker propeller. This was related to the high speed and larger blade surface area of the propeller. While the above described numerical investigations revealed attractive potential of the FR coating for efficiency gain, experimental investigations were conducted to confirm on this potential with a scaled model of the earlier described basis tanker propeller in the Emerson Cavitation Tunnel. The model was constructed from aluminium to a scale of 1:19.57 so that multiple sets of blades, manufactured with great accuracy can be installed or replaced easily. polymer top coat and a tie coat between these two for good bonding. The whole system dried to a film thickness of between 320 and 360mic. The uncoated and coated propeller model can be seen in Figure 6. Figure 5. Loss in efficiency in going from Design Drag Coefficient to specified Rubert Surfaces, Atlar et al (2002). This allowed rapid and reversible changes between the coated and uncoated condition. One set of blades was coated with the IS700 FR system which was a three layer system consisting of an epoxy basecoat, a silicon Figure 6. Model Propeller with uncoated (left) and coated (right) blades, Mutton et al (2005) slight change was due to the slight decrease in the measured torque as observed in the numerical simulations. The open water tests were repeated at a reduced vacuum, which corresponded to the fully-loaded condition of the vessel. This did not show any change in the efficiency at the design operating condition. Results from the tests were discussed by Mutton et al (2005) and Figure 7 shows the findings from the open water tests. As shown in this figure there was little difference between the coated and uncoated condition for the favour of the coated condition at higher values of advance coefficients. The 137 0.35 0.45 Advance Coefficient, J 0.55 0.65 0.75 0.85 uncoated Kt uncoated 10Kq uncoated Efficiency coated Kt coated 10Kq coated Efficiency Comparison of Open Water Characteristics in Atmospheric condition (water speed 4ms-1, Confidence limits 95%) Proceedings of 26th ITTC – Volume I 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0.25 453 However in their experimental study, Korkut and Atlar (2009) withdrew attention coating technology. In parallel to this development, in the early stages of the above described research at Newcastle University the commercial FR system used was International Paint’s Intersleek 700 (IS700). After the introduction of the recent commercial product, Intersleek 900 (IS900), the above propeller performance tests were repeated with this latest coating system applied on the same model propeller by Korkut and Atlar (2009). Using the latest application technology it was possibly to achieve a dry film thickness of 250Pm with the three layer coating system as opposed to a 350Pm thickness of the earlier tests. The open water performance tests revealed an average 1% difference in the efficiency values over the entire J range for the favour of uncoated blades. Both thrust and torque values were slightly increased by 1.9% and 0.9% with the effect of coating, respectively. In overall the difference in the average efficiency was within the uncertainty level of the open water tests which was 3%, similar to the conclusions by Mutton et al (2005) although the trend in the previous tests was in favour of coated blades. Figure 7. Open water curves for the uncoated and coated propeller. A slight reduction in torque at higher advance coefficient has led to an increase in efficiency for the coated propeller. The design operating condition for this propeller is J=0.48; no difference is detected in performance at this condition, Mutton et al (2005). Examination of full-scale propellers coated with FR systems has demonstrated that, like all propeller coatings, the Foul Release coating is prone to suffering damage from to cavitation and hitting objects in the water. This is usually about 5-10% of the coating surface area and predominantly on the blades leading edge, trailing edge and tip regions. It was suggested that this damage may significantly affect the performance of the propeller as well as promoting early cavitation inception and encourage further cavitation development in the damaged areas. To investigate these effects Mutton et al (2005) imparted different levels of typical damages onto this model propeller’s coating to investigate the damage effects. These tests indicated that the damage to the coating had to be extensive before significant reduction in efficiency to occur. One of the important aspects affecting the foul releasing ability of these coatings is the lower threshold of a vessel’s continuous operational speed. Early generation FR coatings had relatively high threshold (e.g. 18 knots and beyond) to be effective whilst this limit has been reducing (e.g. 12 knots and below) with recent development in this Specialist Committee on Surface Treatment 454 on the applied paint thickness such that, owing to the practical limitation of the application technique of the particular coating, which was airless spraying, the coating thickness applied on the model propeller was almost similar to the coating thickness at fullscale. This would require further investigation on scaled coating thickness and appropriate scaling law. Within the same framework another recent experimental investigation on the application of new FR coating on model propeller performance was reported by Atlar et al (2010) as part of the recently completed ECFP6 integrated R&D project AMBIO which aimed to develop non-toxic antifouling benefited from nano technology engineering to prevent or reduce the growth of biofouling in the marine environment, AMBIO (2010). In this project, one of many newly formulated and tested FR coatings was TNO-008 which was based on nano-engineered Sol-gel technology by TNO. This coating was applied on the earlier described benchmark model propeller using spraying technique and cured by heating up to 125 deg. The nature of the coating and the application technology enabled to apply this coating at a desired thickness such that it was possible to achieve an average roughness which was 54% less than the roughness achieved with the Intersleek 900 (IS900). The comparisons of the open water test results of the model propeller with the IS900 and TNO-E008 coatings showed similar torque characteristics, with little difference observed between the 2 coatings. However the TNO-E008 coating gave a higher thrust value for the same rpm when compared to the IS900 coating such that the efficiency increase could be as high as 4% when compared to the IS900 at the maximum efficiency. Whilst this finding appears to be too plausible requiring further investigations at least by applying on other types of propellers and to test, the most interesting nature of this new coating technology was the flexibility in the application thickness that can be adjusted to meet a scaling criterion that can be found between the model and full-scale paint thickness. In order to investigate the effect of propeller coating on ship’s performance in full-scale and controlled manner, Mutton et al (2003) conducted a series of comparative dedicated full scale trials for the first time with the FR coated and uncoated propellers. This was over a measured mile with Newcastle University’s Ex-R/V Bernicia which was based on the design of a fishing vessel and mainly used for estuarine and coastal research. The main particulars of the R/V and its single screw are given in Table 8 and 9, respectively. Table 9. The general particulars of RV Bernicia Overall length 16.2 m Beeam 4.72m Draft 2.59m Gross tonnage 46.25 tons Engine (MCR) 150HP @ 1500rpm Gear box ratio 3.4:1 Maximum ship speed 9 knots Table 10. Main particulars of the R/V Bernicia propeller Diameter 1.14m Mean face pitch 0.9m Expanded BAR 0.466 Blade numbere 4 Rotation Right hand Max rpm 440 138 Kt, 10Kq, Efficiency Proceedings of 26th ITTC – Volume I 455 Mutton et al (2003). As shown in Figure 8, despite the weather affecting the coated trials, the results showed little difference between the shaft power performance of the coated and uncoated propellers. 9.00 9.50 Although the sea trials proved inconclusive due to poor weather, in measuring the short term increase in performance due to the application of the coating, in the first three years since the trials took place, the propeller was inspected at both 12, 24 and 36 months’ The state of the propellers at these inspections are shown at pictures in Figure 9, Mutton et al (2005). Errors estimated at 10% 8.00 8.50 Final Power Curve Comparison Uncoated Trial Coated Trial 7.50 Tide Corrected Speed over Ground (knots) 7.00 Specialist Committee on Surface Treatment 456 4 6 8 10 New Coating 18 20 22 Coating After 1yr in Service 16 Uncoated Propeller 14 Ra value (microns) 12 24 Ra Frequency Distribution for the Uncoated Propeller, the Newly Coated Propeller and after 1yr in Service 2 26 28 was significantly different in favour of the coated propeller. There was some measured difference between the newly applied coating and the coating after 12 months in service. This was mostly due to the presence of the slime layer on the blades which can easily be removed and some slight mechanical damage to the coating. 12 months 24 months 36 months (back) Figure 9.: The coated propeller of Bernicia after 12, 24 and 36 months in service, Mutton et al (2005) 0 Roughness measurements were taken on the Bernicia propeller using stylus type roughness gauge (Surtronic 3+) before and after the coating applied as well as after 1 year vessel was in service with the coated propeller. As shown in Figure 10 the average of the mean roughness amplitude (Ra, with a cut-off length of 2.5mm) and its distribution 40.00% 35.00% 30.00% 25.00% 20.00% 15.00% 5.00% 10.00% 0.00% Figure 11 shows the mean spacing distance between profile peaks frequency distribution (Sm) measured on the Bernicia’s propeller. This is a measure of the surface texture where the larger the value, the more ‘open’ the texture. The coated propeller exhibits a much wider range of mean spacing, while the uncoated propeller had a much smaller range. As shown in Figure 11, after a year in service the frequency distribution of Sm has changed little and still exhibited the wider range. Mutton et al (2005) concluded that the coating significantly changed the roughness characteristics of the propeller blade surface and that the roughness did not change significantly after 12 months in service. The coating had the effect of preventing the increases in roughness usually seen with uncoated propellers as well as keeping the R/V propeller remarkably free from major fouling more than 3 years which was impossible with her uncoated propeller. Figure 10. The mean roughness amplitude, Ra, frequency distributions measured on the propeller of R/V Bernicia before coating, after coating and after a period with the coating in service. % Frequency The initial trials were conducted with its clean but uncoated propeller before being placed on the slip and its propeller removed to be coated by IS700 using spraying at the paint manufacturer’s site. Another series of measured mile trials were then conducted for the same loading conditions applied with the uncoated propeller trials. Shaft torque, shaft/vessel speeds and all other relevant parameter measurements were recorded for analysis and further corrections. The conduct of the trials and analyses were carried out using the BSRA standard procedure and details of these measurements can be found in 6.50 propeller. What fouling was returned is a light ‘slime’ layer that could be easily removed with a damp cloth. This was very different for the uncoated propeller where after 14 months in service after a polish, hard shelled barnacles were present to about half the blade radius that can only be removed by scrubbing.. 139 140000.00 120000.00 100000.00 80000.00 60000.00 40000.00 20000.00 0.00 6.00 As shown in these pictures the coating was found to be in good condition, 95% intact, except for slight removal of the coating at the edges and tip of the blades. The results have shown that despite the vessel operating in a heavy fouling, coastal and estuarine environment, little fouling was returned to the Figure 8: The final Results of the Bernicia sea trials show no statistical difference between the two curves. The trials were particularly affected by the weather leading to large error estimates and making the results inconclusive, Mutton et al (2005). Corrected Shaft Power (Watts ) 0 500 1000 2500 New Coating 1yr in Service Uncoated Propeller 2000 Sm Value (Microns) 1500 3000 3500 Sm Frequency Distribution for the Uncoated propeller, Newly Applied Coating and After 1yr in Service Proceedings of 26th ITTC – Volume I 90.00% 100.00% 80.00% 70.00% 60.00% 50.00% 40.00% 30.00% 20.00% 10.00% 0.00% 4000 457 Figure 11. The mean spacing between profile peaks, Sm, frequency distribution. Measured on the propeller of Bernicia before coating, after coating and after a period with the coating in service. In the case of a “surface” cavitation, as oppose to a “vortex” type, inception occurs in the region of the boundary layer transition. In this respect, propeller blade roughness stimulates the transition of the boundary layer from laminar to turbulent flow and hence causes cavitation inception. The Foul Release coatings are expected to delay such transition from the laminar to the turbulent flow and hence the associated delay in cavitation inception will also be expected. However, this effect may not be so important for full-scale propellers which operate in fully turbulent regime. Even if it is limited to the leading edge regions, this effect can be important for special propellers designed to avoid cavitation. Another interesting nature of the visco-elastic materials, like the silicon coating, is their effect to alter the turbulence characteristics of the flow near the wall and even “relaminarise” the turbulent flow. This will not only affect the cavitation inception but also influence the characteristics of the developed cavitation. In contrast, the protuberances of uncoated and not well-maintained rough blade surfaces are expected to destabilise the vortices more quickly and creating bubble residence locations, and hence reduce the cavitation strength of the water. Task 2.3. The Effect of Coating on the Cavitation Behaviour The effect of coating on the cavitation performance of a propeller can be as important as on its efficiency or even more for a quiet propeller. Nevertheless, there is hardly any data reported on this subject in the open literature except some anecdotal reporting from full-scale and limited experimental investigations conducted at Newcastle University. These investigations have focused on the effect of different types FR coatings on the cavitation inception, and type and extent of fully developed cavitation observed on the earlier mentioned bench mark tanker propeller tests summarised in the following. Cavitation inception is a complex phenomenon which is far from being completely understood at present. The mechanisms underlying this phenomenon are thought to be threefold: (1) water quality (mainly nuclei content and its statistics); (2) the growth of the boundary layer over the blade sections; and (3) type of cavitation to be developed. Amongst them, it is most likely that the growth of the boundary layer will be most affected by the presence of coating while the type of cavitation may also be affected. Specialist Committee on Surface Treatment 458 In the case of “vortex” type cavitation, particularly in the tip vortex type, the nature of the vortex is strongly dependent upon the nature of the boundary layer over blade in the tip region, which can be affected by the coating. If the boundary layer separates near the tip then the tip vortex will be attached to the blade while the preservation of a laminar flow near the tip can avoid the detachment of tip vortices. The effect of FR coating on the cavitation inception was first reported by Mutton et al (2006) on the tests conducted in the Emerson Cavitation Tunnel with the earlier described benchmark tanker propeller. The model of this propeller was tested with its blades uncoated and coated with Intersleek 700 (IS700) in uniform flow at reduced vacuum levels simulating the loaded and ballast operating conditions of the tanker. Careful recordings of the cavitation inception of a thin unattached tip vortex indicated slight delay in inception due to the FR coating in the loaded condition whilst this trend was somehow reversed in the ballast condition. In overall it was concluded that the effect of coating on cavitation inception was not significant. On the other hand, the nature and extent of the developed cavitation patterns, which were mainly tip vortex and sheet cavitations, were somehow different such that the uncoated propeller tip vortex was thicker while the extent of sheet cavitation was relatively large compared to the coated propeller blade cavitations. However, the uncoated propeller cavitation pattern was more stable compared to the coated one. The unstable nature of the coated sheet cavitation sometimes caused it to break up into misty and cloud types of cavitation along the lower boundary of the cavity sheet. Although it was not published the effect of coating damage on cavitation was also explored by various scenarios and no evidence was found that the coating damage would cause further cavitation on this propeller model. In a recent follow up investigation to the above study, Korkut and Atlar (2009) conducted further experimental investigations onto the effect of coatings on the cavitation inception and cavitation extent on the same benchmark propeller but using latest commercial FR product, IS900. Furthermore they also explored the effect of non-uniform flow by testing the model propeller behind a wake screen. The results of the inception/desinence test are shown in Table 11 where the cavitation inceptin number is defined based on the resultant flow velocity combined with the advance speed and rotational speed at 0.7R. 0.606 0.683 0.685 0.611 0.677 0.679 0.701 0.980 0.982 0.695 0.983 0.984 Table 11. Cavitation inception test results with uncoated and coated blades in uniform and nonuniform flow cases, Korkut & Atlar (2009) Uniform Non-Uniform Uncoated Coated Uncoated Coated Cavitation Type Unattached tip vortex cavitation-inception Unattached tip vortex cavitation-desinence Attached to all blades 140 % Frequency Proceedings of 26th ITTC – Volume I As shown in the table the coating of the blade did not change the cavitation inception characteristics of the model propeller (difference is less than 1%), if the coating applied correctly (i.e. avoiding sagging of paint at sharp blade edges that may cause unrealistic cavitation pattaern and singing). Korkut and Atlar related this to the similar roughness and surface texture characteristics of both uncoated and coated blades measured with the model. However this may not be the case in full-scale applications, where some advantage of smooth FR surface finish can be expected, by delaying the inception of cavitation. As far as the cavitation extent was concerned, the uncoated blades displayed slightly more extended cavitation than those of the coated blades from tip vortex to sheet vortex type for both loading conditions as 459 shown in Figure 12 for the fully loaded condition. In a recent study by Sampson and Atlar (2010) the cavitation inception and extent characteristics of the same model propeller were compared as uncoated, coated with IS900 and the earlier described AMBIO project coating (TNO-E008). These tests indicated some delay in cavitation inception for IS900 compared to the uncoated and TNO-008 coated blades. Analysis of the cavitation patterns was subjective owing to the resolution of the video camera. The predominant cavitation on the blade was steady sheet cavitation and developed tip vortex cavitation in the propeller slipstream which had greater extent on the uncoated blade and similar but slightly less presence on the coated blades with non-discernable difference between them as shown in Figure 13. J=0.50 Uniform J=0.50 Non-Uniform J=0.40 Non-Uniform J=0.40 Uniform Specialist Committee on Surface Treatment 460 (a) (b) Figure 12. Cavitation developments in uniform and non-uniform flow conditions at varying advance coefficients for fully loaded condition: (a) uncoated; (b) coated by IS900. Korkut & Atlar (2009) Figure 13. Cavitation comparison of the 3 blades (Uncoated, IP900, TNO-E008) at J = 0.35 and atmospheric condition. Atlar et al (2010) Similar to the lack of research on cavitation, virtually there is also no published data on the effect of FR coating on propeller noise available in the open literature, apart from the limited investigation conducted at Newcastle University by Mutton et al (2006) and Korkut & Atlar (2009). Of the above four mechanisms of generating propeller noise the first two are associated with “non-cavitating” propeller flow while the latter two with the “cavitating” water by the blade profiles; (2) immigration of flow from the pressure to the suction side of the blades in developing thrust; (3) fluctuating volume of cavitation on the blades when cavitation develops on the blades of propeller operating in non-uniform wake flow; and (4) collapse of cavitating bubble and/or bursting of a cavitating vortex. Task 2.4. The effect of Coating on Comfort (Propeller noise) There are four principal mechanisms by which a propeller can generate sound pressures in water, Carlton (2009). These are associated with: (1) the displacement of the 141 Proceedings of 26th ITTC – Volume I flow. The non-cavitating component of sound pressures will have distinct tones – known as the blade rate noise- associated with discrete (lower) blade frequencies together with a broad-band noise at higher frequencies. The blade rate noise is closely associated with the unsteadiness caused by circumferentially varying wake field in which the propeller operates. This causes a fluctuation in the angle of attack of the propeller blade sections and hence sound pressure. However this can hardly be affected by the presence of the coating. On the other hand the broad-band noise is mostly affected by the level of turbulence in the incident flow and its interaction with the wall boundary layer which will be affected by the coating. One of the important mechanisms contributing to the broad-band noise is the trailing edge noise, which is perhaps the least well understood mechanism. The role of the turbulence in the boundary layer is a crucial parameter, which will be affected by the presence of coating, while this noise component would suffer from the effect of possible fouling with uncoated propeller as well as from hydro-elastic effects of the coated blades. The collapse of cavitation bubbles creates shock waves and hence cavitation noise. This is manifested as mostly ‘white noise’ in a frequency band up to around 1MHz. It is thought that the coating will mostly affect the trailing edge noise and may even act as a damper by absorbing the energy of cavitation noise due to its flexible nature. The investigation of the effect of FR coating on propeller noise was also part of the experimental work on the efficiency and cavitation investigations with the benchmark propeller reviewed earlier. The noise investigations therefore conducted at two experimental campaigns: in the first, the benchmark model propeller uncoated and coated with IS700 tested in uniform flow; in the second campaign the same model propeller coated with IS90 and tested behind non-uniform flow as well as the uniform flow. 461 The comparative results of the first experimental measurements, which were analysed using the ITTC analysis and correction procedure, presented as the net sound pressure level of the propeller against the centre frequencies for the uncoated and coated blades at the fully loaded and ballast conditions as reported by Mutton et al (2006). The comparisons indicated that there was some effect of the coating and the beneficial effect appeared limited to the broadband frequencies and the higher advance coefficients. At smaller values of advance coefficients, which covered the design advance coefficient, the uncoated propeller exhibited reduced noise levels compared to the coated one. In the discrete frequency range there was hardly any discernable difference between the two. As the cavitation increased (as in the ballast condition) the difference between the noise levels of the uncoated and coated propeller at smaller advance coefficient diminished. The recent follow up investigations by Korkut and Atlar (2009) measured the comparative noise levels of the benchmark model propeller, and analysed and presented in the similar manner to the previous investigation. However they used IS900 to coat the blades and also included the effect of flow non-uniformity by wake screen. Typical comparative presentation of their measurements in uniform flow is shown in Figure 14 for fully loaded condition. From these measurements it was concluded that whilst the coating of the blades reduced the noise levels in non-cavitating condition (i.e. higher advance coefficients, J=0.75-0.60), it slightly increased in the developed cavitation condition. This finding applied to both fully loading and ballast condition in uniform and non-uniform flows. Interaction with bio-fouling As stated earlier the effect of fouling is a rather important but complex phenomenon and hence to prevent and reduce the fouling Specialist Committee on Surface Treatment 462 settlement on any surfaces, including propeller blades, should be the prime target rather than assessing or modelling of the fouling effects. Within this framework numerous end-user-testimonies and 4 years of monitoring of the Newcastle University R/V Bernicia propeller reveal that FR coating can effectively stay on blades more than 3 years almost 85-90% percent of the coating intact. For example, Figure 14 shows the state of the FR coating (IS700) on the propeller of the earlier mentioned tanker vessel after 37 months in service. During this period the coating has clearly prevented the major fouling development except the slime fouling. This beneficial effect was even more obvious on the Newcastle University R/V propeller as shown in Figure 15 where the uncoated propeller (after 14 months) is compared with the FR (IS700) coated propeller (after 24 months). It was noted that the uncoated propeller was covered with hard shelled barnacles that had to be removed by abrasive means or scrapers, Mutton et al (2003). In contrast the slime or even barnacles that may be attached to FR coated surfaces could be removed by pressure washing or gentle sweeping action. The effect of slime on any type antifouling is a pretty well-known and complex issue, and experience so far with FR coatings indicates that this coating type suffers more from the slime compared to other types, since slime film will attach more strongly to foul release surfaces than other fouling organisms. Experimental studies with FR coatings indicated that increasing the flow shear can reduce the thickness of the slime layer but not remove completely, e.g. Klijsnstra et al (2002). While this may compromise the initial drag benefits of FR coatings, at higher speeds that propeller blades operate, this benefit may still persists due to thinner layer of slime film as discussed by Candries et al (2003). This is a rather topical issue currently attracting much research supported by paint manufacturers and ship owners. In an attempt to model the coating roughness including the bio-fouling effect on ship resistance the recent study by Schultz (2007) is worthy to note. In this study the resistance-roughness characteristics of some coating types on flat surfaces, which are exposed to different grades of roughness and bio-fouling (varying from slime to heavy calcareous types) settled in a controlled environment, have been established by using a similarity law scaling procedure proposed by Granville (1958) and (1987) based on the similarity between smooth and rough wall boundary layers. 142 Proceedings of 26th ITTC – Volume I 463 Figure 14. Effect of coating on noise levels of model propeller for at varying advance coefficients in uniform flow for fully loaded condition. Specialist Committee on Surface Treatment 464 Figure 14. Face and back view of the benchmark tanker propeller painted by IS700 FR coating after 37 months in service without any cleaning x Propeller coating has always been interest to ship owners by multiple Although this study is only representative and requires further proof, its potential implication in assessing performance losses due to deteriorated blade surfaces including various grades of bio-fouling can be plausible since the procedure is generic and technically can be applied to the blade sections based on the flat plate approach as applied in e.g. Atlar et al (2002). However further roughness data of different types of coating in controlled environment may be required for the simulation of typical propeller surfaces. Figure 15. R/V Bernicia propeller uncoated after 14 months in service (left); coated by IS700 after 36 months in service without cleaning (right) This procedure enabled Schultz to predict the effect of a given roughness on the frictional resistance of a plate of arbitrary length (i.e. representing ship surface) based on laboratory-scale measurements of the frictional resistance and roughness function of a smaller flat plate covered with the same roughness. Schultz applied this procedure to predict the roughness and fouling penalties of a US frigate demonstrating as high as 86% penalty for the heavy calcareous fouling case. Concluding remarks 143 Proceedings of 26th ITTC – Volume I x In spite of various anecdotal claims there has been no credible evidence from full-scale to demonstrate any gain/loss from a vessel fitted with newly polished propeller and FR coated one. However there is limited evidence that these coatings can provide the propeller surface with roughness and texture levels similar to newly polished surfaces for a long time after its applications. This will provide savings in propeller efficiency and maintenance cost relative to the efficiency and cost of unpolished propellers in-service. reasons amongst which the prevention/reduction of galvanic corrosion and that of bio-fouling are the well recognised ones. Recent developments in foul release coating technology and increasing number of FR coated propellers indicates that these coatings have most of the desired properties of propeller coating and currently the most suitable system for development of a propeller coating. x There is no published report of dedicated trial or model test on the comparative efficiency, cavitation and noise emission characteristics of a propeller as uncoated and coated with FR coatings apart from a single source. Limited amount of tests conducted in this source with a model propeller with the coated and uncoated blades have not revealed any remarkable difference in the open water efficiency, cavitation inception and extent as well as the REFERENCES Mosaad, M., 1986, “Marine propeller roughness penalties”, Ph.D. Thesis, University of Newcastle upon Tyne. 465 x x x Validation and verification studies involving model and full-scale performance of coated propeller will require standard measurement procedures and reliable measurement tools, which are preferably optical and practical to use in model and full-scale, for the measurement of appropriate blade surface characteristics. Semi-empirical expressions used for the frictional drag coefficient of uncoated propeller blade sections need to be modified to take into account surface roughness effect of coated sections properly. This will in turn require drag-roughness correlation studies with foul release coated surfaces, preferably including the effect of slime. Propeller model tests with coated blades suffer from appropriate paint thickness at model scale due to practical limitation of the application method with commercial FR coatings. This requires further investigations. measured noise levels despite some small variations in these characteristics due to the effect of coating. x There is a need for dedicated comparative full-scale trials and observations to accurately assess the effect of coatings on the propeller efficiency, cavitation and noise emission. Glover, E.J, 1987, “Propulsive devices for improved propulsive efficiency”, Trans. IMar(TM), Vol. 99, Paper 31, London. Specialist Committee on Surface Treatment 466 Thomas, T.R., 1999, “Rough surfaces”, 2nd edition, Imperial College Press, London. Carlton, J., 2007, “Marine propellers and propulsion”, Butterworth- Heinemann Ltd., Oxford. Townsin, R.L., Byrne, D., Svensen, T.E., Milne, A., 1981, “Estimating the technical and economic penalties of hull and propeller roughness”, Trans. SNAME. Townsin, R.L., Spencer, D.S., Mosaad, M., Patience, G., 1985, “Rough propeller penalties”, Trans SNAME. Musker, A.J., 1977, “Turbulent shear-flows near irregularly rough surfaces with particular reference to ship hulls”, PhD Thesis, University of Liverpool. Broersma, G., Tasseron, K., 1967, “Propeller maintenance, propeller efficiency and blade roughness”, International Shipbuilding Progress, Vol. 14. Grigson, C.W.B., 1982, “Propeller roughness, its nature and its effect upon the drag coefficients of blades and ship power”, Trans. RINA, Vol. 124. Candries, M., 2001, “Drag, boundary-layer and roughness characteristics of marine surfaces coated with antifoulings”, PhD Thesis, University of Newcastle upon Tyne. Candries, M., Atlar, M., Anderson, C.D., 2001, “Low-energy surfaces on high-speed craft”, HIPER 2001, 2nd International conference on high-performance marine vehicles, 2-5 May, Hamburg. Holzapfel, A.C.A., 1904, “Ships compositions”, Trans Institution of Naval Architect, 46. Kan, S., Shiba, H., Tsuchida, K., Yokoo, K., 1958, “Effect of fouling of a ship’’s hull and propeller upon propulsive performance”, International Shipbuilding Progress, Vol. 5, pp. Dashnaw, F.J., Hochrein, A.A, Weinreich, R.S., Conn, P.K., Snell, I.C., 1980, “The development of protective covering systems for steel and bronze ship propellers”, Trans. SNAME Vol. 88. Coldron, J.O. and Conde, J.F.G., 1990, “….”Intl workshop on marine roughness and drag, Paper 5, RINA. Matsushita, K., Ogawa, K., 1993, “Ship hull and propeller coatings using non polluting and anti-fouling paint”, Paper 24, ICMES 93-Marine System Design and Operation.. Anderson, C.D., McKenzie, R.R., Ransom, C.J., Tighe-Ford, D.J., 2003, “Effect of a Paint Coating upon the Modulations of ICCP Current Outputs Produced by Model Warship Propeller Rotation”, 2nd International Warship Cathodic protection Symposium and equipment Exhibition, Shrivenham, UK. Atlar, M., 2003, “More than antifouling”, Marine Engineers Review, March. Brady, R.F., 1997, “In search of non-stick coatings”, Chemistry and Industry. Brady, R.F., Singer, I.L., 2000, “Mechanical Factors favouring release from Fouling Release coatings”, Biofouling, Vol 15. Anderson, A.C., Atlar, M., Callow, M., Candries, M., Townsin, R.L., 2002, The development of foul-release coatings for seagoing vessels”, Journal of marine design and operations, Part B4, IMarEST. Berglin, M., Lnn, N. and Gatenholm, P., 2003, “Coating Modulus and Barnacle Bioadhesion”, Biofouling, Vol 19S. 144 Proceedings of 26th ITTC – Volume I Milne, A., 1977, “Coated marine surfaces”, UK Patent 1470465 and “Antifouling marine compositions”, US Patent 4025693. Truby, K., Wood, C., Stein, J., Cella, J., Carpenter, J., Kavanagh, C., Swain, G., Wiebe, D., Lapota, D., Meyer, A., Holm, E., Wendt, D., Smith, C. and Motemorano, J., 2000, “Evaluation of the performance enhancement of silicone biofoulingrelease coatings bu oil incorporation”, Biofouling, Vol 15. Millett, J., Anderson, C.D., 1997, “Fighting fast ferry fouling”, FAST'97, Vol. 1. Townsin, R.L., Dey, S.K., 1990, “The correlation of roughness drag with surface characteristics”, International Workshop on Marine Roughness and Drag, R.I.N.A., London. Candries, M., Atlar, M., Mesbahi, E., Pazouki, K., 2003, “The measurement of the drag characteristics of Tin-free Self-Polishing Co-polymers and Fouling Release coatings using a rotor apparatus”, Biofouling,19S. Candries, M and Atlar, M., 2003, “On the drag and roughness characteristics of antifoulings”, Intl. Journal of Maritime Engineering, RINA, Vol. 145, A2. Candries, M., Atlar, M., 2005, “Experimental investigation of the turbulent boundary layer of surfaces coated with marine antifoulings”, Journal of Fluids Engineering, ASME, Vol 127. I.T.T.C., 1990, Report of the Powering Performance Committee, Proceedings of the 19th International Towing Tank Conference, Madrid. Candries, M., Atlar, M., Paterson, I., 1999, “Cavitation tunnel tests with coated model propeller”, Marine technology report, University of Newcastle. 467 Atlar, M., Glover, E.J., Candries, M., Mutton, R., Anderson, C.D., 2002, “The effect of a Foul Release coating on propeller performance”, Conference Proceedings Environmental Sustainability (ENSUS). University of Newcastle. Burrill, L.C., 1955-56, “The optimum diameter of marine propellers: A new design approach”, Trans. N.E.C.I.E.S., Vol. 72. Atlar, M., Glover, E.J., Mutton, R., and Anderson, C.D., 2003, “Calculation of the effects of new generation coatings on high speed propeller performance”, 2nd Intl Warship Cathodic Protection Symposium and Equipment Exhibition, Cranfield University, Shrivenham. Mutton, R.J., Atlar, M., Downie, M., Anderson, C.D., 2005, “Drag prevention coatings for marine propellers”. 2nd International Symposium on Seawater Drag Reduction, Busan, Korea. Korkut, E. and Atlar, M., 2009, “An experimental study into the effect of foul release coating on the efficiency, noise and cavitation characteristics of a propeller”, SMP’09, Trondheim. website, Atlar M., Unal B., Unal, U.O., Sampson R, Politis, G., 2010. “WP5.2 Hydrodynamic Testing- Executive Summary”, AMBIO Project Report, Deliverable 5.2b1. AMBIO, 2010, Official http://www.ambio.bham.ac.uk/, Approached December 2010. Mutton, R.J., Atlar, M., Paterson, I., Sampson, R., 2003, “The Effect of a Foul Release Coating on the Research Vessel Bernicia”, Report MT-2003-048, School of Marine Science and Technology, University of Newcastle. Specialist Committee on Surface Treatment 468 Mutton, R.J., Atlar, M., Downie, M., Anderson, C.D., 2005, “Drag Prevention Coatings for Marine Propellers”. 2nd International Symposium on Seawater Drag Reduction, Busan, Korea. Mutton, R.J., Atlar, M., Downie, M., Anderson, C.D., 2006, “The effect of a foul release coating on propeller noise and cavitation” Advance materials and coatings symposium, RINA, London. Klijnstra, J.W., Overbeke, K., Sonke, H., Head, R. and Ferrari, G.M., 2002, “Critical speeds for fouling removal from a silicone coating”, 11th International congress on marine corrosion and fouling, San Diego. Candries, M., Atlar, M. and Anderson, C.D., 2003, “Estimating the Impact of newgeneration antifoulings on ship performance: The Presence of slime”. Journal of Marine Engineering and Technology, Part A, Procs. IMarEST, (A2). Schultz, M. P., 2007, “Effects of coating roughness and biofouling on ship resistance and powering”, Biofouling, 23:5. for surface Granville, P.S., 1958, “The frictional resistance and turbulent boundary layer of rough surfaces”. Journal of Ship Research 2: 52-74. methods The following table gives an overview over the most common formulas how to calculate roughness. Each of the formulas listed in the table assumes that the roughness profile has been filtered from the raw profile data and the mean line has been calculated. The roughness profile contains n ordered, equally spaced points along the trace where yi represents the vertical distance from the mean line to the ith data point. most common one. Since these parameters reduce all of the information in a profile to a single number great care must be taken in applying and interpreting them. Task 3: Review the existing measurement roughness at modelscale and at full scale 3.1. Roughness Parameters Surface roughness in general is a measure of the of the texture of a surface. It is quantified by the vertical deviation of the real surface from its ideal form; in case of large deviations we speak about a rough surface. Roughness values can either be calculated on a profile or on a surface. Profile roughness parameters (Ra, Rq….) are more common whereas area roughness parameters (Sa, Sq,….) give more significant values. There are many different roughness parameters in use, but Ra (Rah) is by far the 145 Proceedings of 26th ITTC – Volume I The most commonly used roughness parameter is the Average Hull Roughness parameter Rah representing the mean of all the vessel’s hull roughness readings. 3.2. Measurement Techniques For the measurement of roughness stylus instruments and optical instruments are in use. In the shipbuilding industry the BMT Sea 469 The standard roughness unit is the peak to trough height in microns per sample (one sample is of 50 mm length of the underwater hull). Tech Hull Roughness Analyser (a stylus instrument with a surface probe) is accepted as the industry standard instrument for the measurement of hull roughness. Specialist Committee on Surface Treatment 470 3.3. Full Scale Measurements The hull roughness normally is measured in the way that the hull is divided into 10 equal sections with 10 measurements each, 5 on the port and 5 on the starboard side. A total 3.4. Roughness Measurements on Ship Models of 50 readings are taken on each side, 30 on the vertical sides and 20 on the flats. From the 100 measuring locations, the Average Hull Roughness is calculated. Roughness measurements on ship models are carried out (e.g. MARIN, SSPA) but the results of the measurements are used for quality assurance and not for further investigation. Most of the Model Basins do not measure the roughness of the model’s hull. 1. Measurement equipment Task 4: Propose methods that take into account surface roughness and other relevant characteristics of coating systems; check the need for changes to the existing extrapolation laws. This chapter will outline recommendations regarding procedures in measuring skin friction on rough surfaces aimed at the maritime sector. Several different techniques can be used for measuring skin friction on rough surfaces some better suited than others. In no specific order the following can be mentioned: Flat plate in towing tank Flat plate in cavitation tank 146 Proceedings of 26th ITTC – Volume I Flat plate in towing tank Flat plate in open water channel Pipe friction device Flow cell Couette cell Other shapes than flat plate in towing tank or the like such as ax symmetric body or model ship Full scale tests 1.1. In the committees opinion the best combination of accuracy and complexity. Usually a quite large surface can be coated, and if care is taken with the setup and rigging of the plate, reproducibility is usually excellent. The longer and thinner the plate is the better, as skin friction resistance ratio to total resistance will increase with those parameters. Towing speed is limited (to usually around 5m/s) which does require some more extrapolation to full scale than for instance cavitation tank. Re-rigging after a new surface has been applied can be quite sensitive, therefore control of reproducibility is very important. Time between tows can also be important as a flat plat (especially if towed horizontally) is sensitive to small changes to angle of attack caused by vortical flow remaining in the towing tank after a test. 1.2. 471 Flate plate in Cavitation tank Skin friction measurements can be achieved by two methods. 1.2.1. Floating element measurements A plate is built with the sample coated on the plate (and/or before the plate), with a very small gap between the measurement plate and the flush surrounding plate. This plate is suspended in such a way that it is fixed, but shear forces can recorded, usually by strain gauges. To avoid edge effects the gap is critical, and step changes in roughness should be avoided by coating before and after the test section. 1.2.2. Boundary layer measurements Measuring the boundary layer by for instance LDV (Laser Doppler Velocimeter), the velocity shift in logarithmic boundary layer can be recorded. where U+ is the non-dimensional wall velocity, y+ the wall distance and is the velocity shift function, also known as the roughness function. Critical is the extraction of the friction velocity u and several methods have been proposed. This committee has no recommendations regarding which one to use. Specialist Committee on Surface Treatment 472 1.3. Pipe Friktion Measurements The above equations can be used for any type of skin friction measurements, the difference between boundary layer methods is that friction velocity is used directly, whereas resistance measurements should use the second version of the equation. Boundary layer measurements are very time consuming and requires expensive and sensitive measurement equipment. But better control of displacement thickness is possible than indirect methods. or if boundary layer measurements are not available (as for instance towed plate or floating element measurements) Figure 4: Velocity profile measurements on different rough surfaces Once the velocity shift function is established by boundary layer measurements, it relates to the skin friction coefficient as where s and r refers to smooth and rough respectively. Therefore for all boundary layer measurements (and skin friction measurements in general) it is important to measure the hydraulically smooth case. The above equation is a simplification of integration of the log-law boundary layer equation, and assumes that the displacement thickness is constant. Depending on the type of measurement, care must be taken to either ensure that the assumption holds, or otherwise correct for the simplification. For boundary layer measurements for example momentum or outer similarity methods can be used, but will not be described further in this report, see for example. Finally, skin friction can be related roughness by the non-dimensional roughness height Pipe friction measurements is probably the most cost effective method along with Couette Cell flow. It is also well suited for tests with for example bio fouling as the test 147 Proceedings of 26th ITTC – Volume I pipes can be transported relatively easy between test site and fouling site. Flow Cell Measurement method is indirect as measured parameters is average flow velocity and pressure drop over test section. Accuracy is much lower than for instance towed flat plate however for surfaces with high skin friction increase it is deemed sufficient (as for instance barnacle surface). Boundary layer is not free (confined by the pipe radius) and correction to flat plate skin friction must be performed. 1.4. Couette Cell Mainly mentioned to include types of tests. Flow cell is not well suited skin friction measurements within the maritime sector as Reynolds number is very low and requires too extensive extrapolation to full scale skin friction. 1.5. Couette cell is relatively simple in construction and build cost. It does however produce results which is difficult to interpret accurately due to mainly the formation Taylor-Couette cells, complex axially nonuniform boundary layer and boundary layer development, but also issues such as increasing water temperature during tests. Reynolds Number 473 Therefore, some difficulty exists calculating Cf based on torque measurements, but [Arcapi, 1984] suggested where is the von Karman constant and Reh is the Reynolds number based on the gap length between cylinders. Other shapes Advantage with Couette cells is that it is rather easy to apply a new surface, and especially for tests which require measurements over long time (for example to test self polishing) Couette cell is well suited. 1.6. Generally using other shapes than flat plate for towing, seems like an unnecessary complication in model scale. The goal of skin friction measurements is to acquire skin friction lines which can be extrapolated to full scale. Using for example a ship model will introduce much higher residual and wave resistance than for a flat plate, but even more important large variations of skin friction locally due to accelerating flow around the model. This makes it difficult to interpret extracted increase in resistance. It is therefore not a recommended procedure. There is another reason to keep Reynolds number relatively high which is that the results will require less extrapolation to full scale. Cf smooth can be taken from any source, for example Cf,ITTC. case the Reynolds number is too low for measuring any effect related to skin friction (exceptions does exist as for example ribblets or active surfaces), and results will be of very questionable value. 2. Test Procedure Recommendations 2.1. It must be ensured that the Reynolds number is sufficiently high. The lower the Reynolds number the higher the risk is that the surface becomes hydraulically smooth. This is the case no matter what measurement equipment is being used. Theoretically, the surface is hydraulically smooth when y+ is lower than 5. If this is the Flow speed Specialist Committee on Surface Treatment 474 2.2. At least 2m/s above hydraulically smooth must be tested. If not it will be difficult to perform regression analysis and extract parameters such as efficiency for the given surface. Ideally points should be fairly dense for more confidence in regression analysis, but also to identify possible problems with the test equipment/measurement method. Reference surface For some test equipment this can present a problem, especially in a towing tank. Therefore it is recommended that it is possible to fulfil this recommendation before tests commences. 2.3. To be able to compare different surfaces skin friction, it is imperative that all measurements are completed with reference to a hydraulically smooth surface. Most measurements are unfortunately reference to another rough surface, for example SPC to silicone. This makes it impossible, or at the very least quite difficult to collect results from many different sources. Therefore at least one measurement must be carried through with a hydraulic smooth surface Reproducability where y+=5 is the limit. This value will for most test setups be in the range 5-50m, so some polishing of for example a primer will usually be necessary. 2.4. Reproducability will vary quite a lot between different measurement equipment. Two levels of reproducibility exists, with and without re-rigging. A full ITTC uncertainty analysis would be the best procedure to follow, but at least for some measurement techniques will require too much additional work. Minimum. Repeat 3 measuring points 3 times without re-rigging Recommended. Same as test 1, but completed twice between re-rigging. Re-rigging implies that the setup is dismantled to a degree where a new surface can be applied. Surface Reproducibility is paramount, especially for testing for example coatings, as difference between coatings and hydraulically smooth is quite low (below 20% for most cases and Reynolds numbers), between most commercial coatings below 10%. If reproducibility is only 5% it will have a significant impact on the analysis. Many factors can produce low reproducibility. This committee is aware of the following error sources. Towing tank: Poor alignment of plate, too little time between tests, suspension allowing plate to bend or Yaw. Cavitiation tank: Not stiff enough floating element increasing gap size, test section not flush with surroundings, scatter in LDV measurements. Pipe friction device: Reproducability in measurement of average flow velocity, nonflush pressure tap. Couette cell: Temperature change between and under tests 2.5. Two aspects of the surface must be considered Application Roughness height (and possibly other parameters) Application of commercial coatings must be completed in a fashion similar to the procedure at the shipyard. For instance, temperature and humidity range from the supplier must be followed, if high pressure spray system is required the surface topology and roughness height can change significantly from the intended if a low pressure system or roller is used. 148 Proceedings of 26th ITTC – Volume I The committee agrees that steel/primer surface need not be considered. Even though a real untreated hull surface is not smooth, applying the coating system usually consisting of multiple layers, most of the steel roughness will be masked by the coating. This is off course not the case for welding seems for example, but taking such imperfections into account will be practically impossible. A further (very small) added friction could eventually be proposed. Roughness height measurement should preferably be completed with a BMT roughness analyser. However, other devices can be used, if they as a minimum produce a measure of Ra. MA can perhaps add to this. Other parameters can be added such as average distance between roughness elements for barnacles for instance. This might be usefull at a later stage when a relatively high number measurements are collected. 3. ITTC Rough Skin Friction Database It is proposed that an international database of skin friction measurements are created. Many different researchers have measured skin friction on a lot of different surfaces seen on a ship hull. This includes coatings, bio-fouling and bio-films. As no single facility will have the funding available to test every coating, bio-fouling and bio-film surface, the second best option is to analyse results following the same guidelines and procedures. Tests have been completed with test equipment as described in section 1.1 at varying Reynolds numbers, facilities, surface size, roughness height measurement method (if any) and so forth. Many tests are also referenced to another coating and not a hydraulically smooth surface. Procedure 475 It is therefore at present difficult to collect skin friction lines and present them in the same figure. For experiments which fulfil the test procedure recommendations in chapter 2, it will however be possible to collect and compare the results. 3.1. SSPA and Newcastle University will jointly be responsible for creation and maintaining the homepage, and evaluate and present new results. Submission of results After submission of results hydro dynamist from either SSPA or Newcastle Uni. will evaluate results submitted (see 3.2), and determine if results can be used. After analysis is completed results will be publically available on the homepage. 3.2. Any party can submit results completing the submission form and appending data in electronic form. At a minimum raw measurement data and analysis to skin friction coefficient must be supplied, along with description of analysis method. Unless requested otherwise all material submitted will be publically available. It is assumed that at a minimum the material can be used to extract necessary data by RSFD and present it together with other results. RSFD will evaluate the material in accordance to items described in Chapter 2, and decide a confidence level and whether or not results will be added to the database. The submitter will have the option to comment on the results before they are made public on the homepage. Skin friction line, velocity shift function parameters and roughness height will be the main publicised results compared to CF,ITTC. All supplied material will be made available on ftp server (or links to for example papers) Specialist Committee on Surface Treatment 476 Analysis Procedure. unless otherwise requested by the submitter in the submission form. 3.3. 3.3.1. Velocity shift function If results are accepted the analysis procedure will be as follows. Velocity shift function will be used regressively on each skin friction line, however using only one parameter (h) will not be sufficient. Part of the ultimate outcome of SFRD will be to specify the efficiency parameter for various types of surfaces. Bowden added resistance main shortfall is that it is based on a one parameter description of the surface topology which is not sufficient as can be seen in several articles. Many different two (and more) parameter function have been investigated, but it is this committees conviction that using an additional parameter which is not directly measurable by analysing the surface topology is the most viable method. This additional parameter is the efficiency parameter. In stead of using for description of the velocity shift as a function of roughness height, the efficiency parameter C will be introduced as For each measurement added to the database either the velocity shift (boundary layer measurements) or Cf rough and smooth and roughness height will be known and C can be calculated (by least squares method along the Reynolds number range measured). It is the hope that collecting many measurements of different types of surfaces, for example silicone surfaces, will reveal a fairly constant value of C, even with varying roughness heights. This will produce a method of calculating the full scale skin friction using the roughness height and a type specific efficiency parameter, rendering a much more reliable method than the Bowden added resistance used today. Velocity shift function also have the advantage that it can be used locally with for example thin boundary layer methods or Elog method for RANS solvers. 3.3.2. Comparison of results The only reliable way to compare results from different institutions/measurement methods is to reference the measurements to a surface with known skin friction line. This can in principle be any type of surface for example a specific SPC coating applied exactly the same way each time. However, the only practical procedure is to always use hydraulically smooth surface. As residual resistance (and wave resistance for some methods) is different for each measurement equipment and design, skin friction lines cannot be compared directly. Therefore, raw results will be reevaluated using the smooth skin friction measurements under the assumption that the only resistance component that changes between tests of different surfaces is the skin friction. Thus only added skin friction resistance will be used The velocity shift function will then be evaluated using a know smooth skin friction line such as CF,ITTC or other lines if deemed more warranted. 149 Proceedings of 26th ITTC – Volume I This procedure will to a large degree remove problems with comparing results between measurement techniques at different facilities. It does require measurements of hydraulically smooth surface, which unfortunately is not available in many measurements. It is conceivable that measurements eventually can be added to the database using other reference surface, but several surface with the correct reference line is necessary before such measurements can be added with confidence. Conclusion and Recommendations 1 ExtrapolationMethods 1.1 Conclusions At this time no evidence suggests that the recommendation of the 25’th Specialist Committee on Powering Performance Prediction regarding the use of the Townsin roughness allowance should be revoked. This does not imply that the committee believes that Townsin/Bowden roughness allowance is an accurate and universal roughness allowance, but that at this point nothing better seems to be available. Based on a skin friction model test measurement database a new or modified roughness allowance should be suggested. Considering the variety of surface roughness on a ship (coating, damage, slime, fouling) it is likely that this new formulation will either be several formulations or at least one formulation but with roughness type dependent parameters. A most likely candidate for an improved roughness allowance is the velocity shift function (Roughness Function), used to generate Bowden or Townsin type formulation for the full scale ship using CFD analysis supported by experimental and full-scale data. 477 Arpaci V.S., Larsen P.S., Convection Heat Transfer, Prentice-Hall, Englewood Cliffs, NJ, USA, 1984 Leer-Andersen M., Larsson L., Andreasson H., Skin Friction Measurements on Rough Surfaces and Full Scale evaluation, 2nd International Symposium on Seawater Drag Reduction, Busan, Korea, 2005 Leer-Andersen M., Larsson L., An experimental/numerical approach for evaluating skin friction on full-scale ships with surface roughness, J. Mar Sci Technol, 2003 All antifoulings suffer from micro-slime (slime) even in newly applied condition. Foul release coating particularly suffers from slime effect due to their non-biocidal defence mechanism which requires shear stress to keep slime free. Recommendations There is a lack of data on the dragroughness correlation of AF-coatings as well as of a new generation of self-polishing types to improve the performance extrapolations not only for the “as newly applied” (trial) condition but also for the “after some time” (in-service) condition. Limited drag-roughness correlation studies indicate that the skin friction of “newly applied” foul release coated surfaces does not correlate with single hull roughness parameters. 1.2 It will not be possible to generate a new formulation without an extensive database of skin friction measurements. A relatively small number of existing datasets which is the basis for all formulations today does not lend credibility to a new formulation which can be used with higher confidence. There is a need for investigation to establish a relationship between the drag-roughness characteristics of surfaces coated either with foul release coatings or with the new Specialist Committee on Surface Treatment Roughness measurement should as a minimum include Ra. Including more surface parameters such as Rt, profile measurements and so forth adds value to the measurements. Foul release coated surfaces suffer from inaccurate measurements in full-scale (as well as in model-scale with relatively large surfaces) with stylus type mechanical surface measurement devices. 478 generation of self-polishing coatings to improve the performance extrapolations. These investigations should be extended for coated surfaces “in-service” as the surface characteristics of coatings change progressively in service, particularly in case of self-polishing coated surfaces. Although this is a challenging task it is the reality in predicting power inservice. 2.2 Recommendation Regarding future work one issue which this committee feels can progress the confidence and accuracy greatly for roughness allowance and its application range is to establish a comparative database for skin friction measurements. 3 PropellerCoatings Conclusions In spite of various anecdotal claims there has been no credible evidence from full-scale measurements to prove any gain or loss from a vessel fitted with a coated propeller compared to a newly polished uncoated propeller. However there is limited evidence that the foul release based coatings can provide the propeller surfaces with roughness and texture levels similar to newly polished uncoated surfaces and even better for a long time after its applications. There is also evidence that these Propeller coating has always been of interest to ship owners by multiple reasons amongst which the prevention and/or reduction of galvanic corrosion and that of biofouling control are well recognized. Recent developments in foul release coating technology and an increasing number of coated propellers indicates that this paint technology has most of the desired properties of propeller coating and is currently the most suitable system for development of a propeller coating. 3.1 Initially as much data as possible following the recommendation for test procedure at least to an extent should be collected and compared after which alternative roughness allowance There is need for data concerning the roughness-drag correlations of flat plat plates coated with foul release as well as with the modern day self-polishing type coatings. Investigations to collect appropriate data are required. The effect of micro scale biofouling (slime) on the paint performance should be included in the performance predictions and hence investigations should be widened to cover this effect which is a hot issue in foul release coatings. 2 ModelTestProcedures 2.1 Conclusions The most accurate method for skin friction measurements probably is the flat plate in the towing tank, but several other methods, including boundary layer measurements, can produce valid results. Tests should be carried out at Reynolds numbers which produce a flow above the “hydraulically smooth surface” to have any meaningful results. For comparison with other experiments it is of high importance that a reference surface is tested which is hydraulically over the Reynolds range. If this is not the case it is impossible to compare tests coming from different facilities. Reproducibility should be tested especially for equipment which needs to be re-installed when changing the surface, e.g. in case of a flat plate in towing tank. Reproducibility with and without re-installing should be checked. 150 Proceedings of 26th ITTC – Volume I coatings can maintain the blade surface free from major fouling for long time without any maintenance. This suggests potential savings in propeller efficiency and maintenance cost relative to the efficiency and cost of unpolished propellers in-service. There is no published report of dedicated trials or model tests on the comparative efficiency, cavitation and noise emission characteristics of a propeller uncoated and coated with foul release coatings apart from a single source. Limited amount of tests conducted with model propellers with coated and uncoated blades have not revealed any remarkable difference in open water efficiency, cavitation inception and extent as well as the measured noise levels despite some small variations in these characteristics due to the effect of coating. Recommendations Propeller model tests with coated blades suffer from appropriate paint thickness in model scale due to application methods with commercial coatings. Although this conclusion applies to any coating, as a generic problem of the foul release type coatings, any validation and verification investigation involving the model and full-scale performance of foul release coated propeller will require a standard measurement procedure and reliable measurement tools for the surface measurements. 3.2 There is growing number of full-scale applications and an increasing interest on propeller coatings. Investigations therefore should continue in this field. There is a need for dedicated model tests, full-scale trials and progressive docking observations to accurately assess the effect of coatings on the propeller efficiency, cavitation and noise performance. At least limited amount round robin tests for open water performances amongst the ITTC community may resolve some current model test related issues. 479 As a generic problem of the foul release type coatings, investigations on the application and measurement of coatings on model propellers (and full-scale) should continue with the objective of devising standard procedures and resolving the scale effect issue involving paint thickness. Semi-empirical expressions used for the frictional drag coefficient and perhaps the lift coefficient of uncoated blade profiles need to be modified to take into account the coating effect. As a generic problem of any coating applied surface the technology investigation of coatings should be extended for the effect of biofouling, at least for the effect of slime which is the natural conditioner of any coating but particularly affecting the performance of foul release coatings. 4 StateoftheArtCoatings Specialist Committee on Surface Treatment 480 measured surfaces. There is a need for the development of “non-contact” based measurement devices providing options for more parameters and hence investigations in this areas should continue Company/institution Submission date Adress Phone Public (Yes/no) Other parameters ITTC Skin Friction Data Submission Form Contact person Appendix: e-mail Appended material (raw data, analysed data, reports, papers) File name (description) 1. 2. 3. Test description 1. Equipment (see document XXX, section 1.1, 1-8). If other please specify 2. Reynolds number range 3. Flow speed range Deliverables Description 1. (name or description) 2. Additional information Roughness height 4. Roughness height measurement type (device and parameter) Short description of test equipment if not standard Conclusions 4.1 3. Surfaces tested Anti fouling technology is under further scrutiny due to environmental concerns. As a result, although currently in small proportion, the applications of foul releasing (non-biocidal) type antifoulings are increasing worldwide requiring further attention and hence further investigation. Recommendation Solid evidence comparing the skin friction characteristics between majorities of coatings is non-existing. Different model evaluation, application and measuring techniques make it very difficult to compare measurements for which reason most of the measurements are only able to state that this coating is xx% better than another coating. 4.2 Measurements of hull surfaces coated with foul release surfaces in dry docks suffer from “contact” problems of stylus in mechanical devices. Furthermore, a single hull roughness parameter is not sufficient to characterize the 151 1 ON THE IMPORTANCE OF ANTIFOULINGS FOR GREEN SHIPS By y Prof. Mehmet Atlar Antifouling economies – SPC Coatings 3 EARLY 1990s data, A. Milne Indirect reduced costs (e.g. bunker transport) 1080M $/y Reduced dry docking costs 800M $/y Extended docking intervals 409M $/y Reduced fuel cost 720M $/y TOTAL SAVING 3,000M $/year Main objective of antifoulings Preventing the attachment of fouling and hence minimising drag is the main objective of marine antifoulings (A/F) Improved drag reduces fuel consumption and in turn GHG emission There are other ways of keeping ship hulls clean but none so far proven to be viable for the vast majority of the world’s world s fleet Keeping ships’ propellers free of fouling is also important from the ship performance point of view NOx SOx • Total CO2 saving: 20M tonnes / year • Rate of CO2 emission: 3.1 ton / Ton-Fuel • Annual fuel saving: 7.4 M tonnes • 2% saving due to improved antifouling performance • 2% saving due to smoother hulls Impact on GHG emission – SPC Coatings COx GHG & Ozon Depleters EARLY 1990s data, A. Milne 2 4 1 152 Antifouling – Current drivers Ship operators are looking at cost more closely than ever Ever increasing and unpredictable fuel prices; financial climate IMO and National Legislations g - IMO/AFS Convention (October 2001) Ship operators have A/F high on the agenda by law New coating technologies and associated products Biocidal / Hybrid/ Non-biocidal ; Ship operators are confused by the claims and counter claims regarding to A/F Operators O t wantt to t be b environmentally i t ll compliant li t (ISO) The environment matters more than ever Ships have to be energy efficient by design (EEDI) and operation (EEIO) – IMO-MEPC 58-59 report on “IMO GHG Study 2009” (April 2009) Biocidal options Currently 90% of the world fleet use these products SPC “Controlled Depletion Polymer” Hybrid SPC “Self-Polishing Copolymer” CDP PRICE 5 7 Antifouling technology options Controlled Depletion Polymer (CDP) Self-Polishing Copolymer (SPC) Hybrid SPC 1. Biocidal option Foul Release (non-stick) 2. Non-biocidal option Foul Release Non - biocidal option CDP TBT free SPC Hybrid SPC Durable & Long lasting Less weight Less paint Lower M&R costs Foul Release Potential fuel savings and lower emissions Currently less than 10% of the world fleet use this product No biocides Low VOC Antifouling Performance Keeps fouling off propellers 6 8 2 153 Noise unsteadiness due to fouling during operations needs separate study – IMO-MEPC 59/19 Correspondence Group report “Noise from commercial shipping and its adverse impacts on marine life“ (April 2009) PE ERFORMANCE Current R & D needs There is increasing interest and applications of foul release coatings due to their environmental and other benefits. Relative merits of these coatings, especially for drag benefits on hulls and p p propellers, , need further R&D including: g To develop a robust, industry based device to measure roughness characteristics of hulls and propellers coated with FR paints in dry docks and labs To establish new skin friction data base and hence roughness allowance associated with these coatings for power estimations Foul release coatings appears to be more vulnerable to slime growth than biocidal coatings. Their drag performance in the presence of slime effect should be evaluated using i special i l model d l and d full f ll scale l testing t ti facilities f iliti Real performance evaluation of hulls and propellers with different coatings needs dedicated full-scale trails with special performance monitoring devices on board Foul release coatings can take advantage of nano-engineered surface patterning that can be further exploited for drag benefits with close collaboration between chemist, marine biologist and hydrodynamicst at the development stage of these coatings 9 Laser profilometer Current R&D Examples New BMT-HRA device 11 12 10 Stylus based BMT -HRA Laser sensor based prototype BMT – HRA Current R & D examples New BMT- HRA using laser sensor Current R&D Examples 25:1 2.3m x 0.25m x 0.01m A unique facility, which is fully-turbulent flow channel (FLOW CELL), has been established to study the adhesion and friction drag characteristics of foul release coatings in the presence of marine bio-fouling, in particular “slime” Measuring section size (L x B x H) FLOW CELL Contraction ratio 256kPa 13.4 m/s 14 slides 76mm x 26mm or single plate 185mm x76mm Max water velocity Test slide capacity Fresh/sea water at 280C-300C Max shear stress Operating medium 3 154 Current R&D Examples 3.35 0.4 0.02 1.5 6 0.6 x 0.28 10 287 167 Umean (m/s) 2 5 7 10 τw (Pa) 11 48 87 167 13 AMBIO (Advanced Nanostructure Surfaces for the Control of Biofouling) was an EU-FP6 Integrated Project. The 5-year project completed in 2010 was highly interdisciplinary including nanotechnology, polymer science, surface science, coating technology, hydrodynamics and marine biology. Project integrated 31 Partners from industries, universities and research organisation and significant end-users industries end users involved There is a need for field data on service performance of coatings using “removable removable test patches” patches and novel ideas for “in-situ measurements” (e.g. using research vessels fitted with special equipment). Current R&D Examples Current R&D Examples Such test (research) vessels with the state-of-the-art f it i systems t performance monitoring (including thrust gauge) will make more realistic contribution into analysis of hydrodynamic performance of different coatings 10000 Re 15000 20000 AKZO19 Cf (B) AKZO20 Cf (B) AKZO21 Cf (B) AKZO28 Cf (B) INT900 Cf (B) STEEL Cf (B) AKZO 19 (Flourinated Slicone blend) displayed favourable skin friction over major commercial brands and patented by IP 0.0034 0.0032 0.003 0.0028 0.0026 0.0024 5000 14 16 4 155 Another facility to investigate the service performance of SPC coatings is “AGING FLUME” which simulates the polishing activity in laboratory condition using seawater in fully turbulent flow condition. Measuring section length (m) Measuring section width (m) Measuring section height (m) Development length (m) Number of plates Size of coated area/plate L×B (m) Water velocity (m/s) Water flow rate (m3/h) Maximum wall shear stress (Pa) Approximately 500 different foul release nano-structured coatings, representing 64 generic coating chemistries were prepared at laboratory-scale and evaluated for their antifouling and foul release performance. Of these, 15 were down-selected for testing in a range of field and end-user tests. Several coatings showed promise in these trials, and have either been commercialized, or have the potential to be so after further develop. 5 novel coatings were patented. Current R&D Examples www.ambio.bham.ac.uk Some of these coatings showed great potential for drag reduction characteristics for hull and propeller applications e.g. e g Fluorinated silicone blends and nano-hybrid nano hybrid sol-gel sol gel coatings with clay nanofilllers, respectively. 15 C f (B) Chemists MARINE ANTIFOULING Marine Biologists Current R&D Examples Ship Owner Naval Architect 17 THANK YOU Marine S h l off School Science and Technology [email protected] 18 [email protected] 5 156 2010年4月16日 ITTIC資料 防汚塗料について 日本ペイントマリン㈱ 山盛 直樹 船底防汚塗料の現状 157 防汚の歴史 BC.400 アリストテレス:船低に“Echeniis”が付着すると船速が低下 BC.300~200 船底の汚損防止にピッチ、蝋、タール、アスファルトを使用 BC 287~212 アルキメデス:船底に鉛を用い、銅のボルトで締める キメデ 船底に鉛を用 銅 ボ ト 締める ルネサンス時代 レオナルド・ダ ビンチ 熔融鉛を船底の汚損防止用に使用 1625年 1685年 1776年 19世紀 1881年 1885年 生物付着防止用に船底を銅板で被服(特許) 船底を虫食いから防止するためタールを塗装(船底塗料の最初の特許) 英国艦隊はすべて銅板で覆う 英国艦隊はす て銅板で覆う 鉄船の時代に入る ⇒ AC塗料の出現 光明社創設 日本特許第1号 「錆止め塗料及びその塗り方」 代表的な付着生物(1) 158 代表的な付着生物(2) 代表的な付着生物(3) 159 防汚塗料の組成 樹脂(塩化ゴム (塩化ゴム・加水分解型アクリル樹脂 加水分解型アクリル樹脂 ・ロジン等) 可塑剤 防汚塗料 体質顔料 着色顔料 添加剤(タレ止め剤 沈降防止剤等) 添加剤(タレ止め剤・沈降防止剤等) 防汚剤 溶剤 船底塗料の世界的動向 (有機スズ防汚剤規制) 2001年10月の国際海事機構(IMO)外交会議での有害な防汚 方法の規則に関する国際条約が採択された。 方法の規則に関する国際条約が採択された 1.2003年1月1日以降すべての船舶に殺生物剤として機能す る有機スズ化合物(トリブリルスズ化合物、トリフェニルスズ化合物) を含有する防汚塗料の塗装の禁止 2.2008年1月1日以降すべての船舶の船体外部表面に殺生物剤 として機能する有機スズ化合物を含有する防汚塗料の存在の禁止 (ブラストし非有機スズ船底塗料に塗り替え、シーラーコート で有機スズ船底塗料を被服する。) 160 船底塗料の法的規制 - 船底塗料はBiocidal Productsとして分類される。 products は殺虫剤/殺草剤のような規制を受ける。 - Biocidal p 塗膜表面の防汚剤 分解 海水中 防汚剤 海水中の防汚剤 堆積物中の防汚剤 環境に対する3つのポイント: 防汚剤の分解速度 付着生物以外の生態 の毒性 付着生物以外の生態への毒性 生体蓄積性 防汚剤の種類 No. CAS. No. 防 剤名 防汚剤名 1 1111-67-7 ロダン銅 2 1317-39-1 化 亜酸化銅 3 137-30-4 Ziram (P 4 330-54-1 DCMU (Preventol A6) 5 971 66 4 971-66-4 P idi t i h Pyridine-triphenylborane lb (PK) 6 1085-98-9 Dichlofluanid ((Preventol A4) 7 13108-52-6 Tems pyridine (Densil S-100) 8 13167-25-4 Trichlorophenyl-maleimid(IT-354) 9 13463-41-7 Zinc pyrithione 10 14915-37-8 Copper pyrithione 11 28159-98-0 Irgarol 1051 12 64359-81-5 Seanine-211 13 1897-45-6 Chlorothalonil 14 12122-67-7 Zineb 15 137-26-8 137 26 8 Thiram 161 分解 付着生物と防汚剤 動物 TBT Cu 防汚助剤 外殻をもつもの フジツボ セルプラ イガイ 外殻をもたないもの ヒドロ ホヤ 植物 藻類 緑藻 褐藻 紅藻 珪藻類 “緑色スライム" “黒色スライム" 防汚剤登録(日本塗料工業会) 2004年以降 「IMO・2001年の船舶に有害な防汚方法の規制に関する 国際条約への適合性に関する(社)日本塗料工業会自主 管理登録品」 として登録および情報公開 162 船底塗料国登録 登録が必要な国々 アメリカ カナダ スウェーデン オランダ アイルランド ベルギー フィンランド オーストリア マルタ ホンコン オーストラリア ニュージーランド 船級登録 船舶の安全航行における環境負荷の低減 Lloyd Germanischer Lloyd DNV KR をはじめとする各船級への登録 163 LF-Sea 船底塗料の分類 船底塗料 分類 (低摩擦) 加水分解型 自己研磨型A/F SPC (従来型) 水和分解型 溶出型 燃 費 崩壊型A/F 拡散型A/F(溶出型A/F) 表面物性 非溶出型 忌避 電気的 等 自己研磨型樹脂の特徴 海水中 + 加水分解 《樹脂が親水化・溶出》 KL/510浬 セルフポリッシング(自己研磨作用) 70 Insoluble spot (平均運行速度:20ノット) 消費 費燃料 60 拡散型塗膜 消耗膜厚 50 自己研磨型塗膜 基盤 40 0 1 2 3 4 5 6 7 8 9 10 11 経過月数 図 運行燃費節減効果 運航後の塗膜の断面写真 164 12 加水分解機構 銅アクリル樹脂 Y C=O C=O XY O (海水:PH=8.2) X O O + Cu++ + C=O R Cu 海水中に溶出 O C=O R 加水分 型 加水分解型(=自己研磨型)塗料用樹脂 磨型 塗 用 有機錫アクリル樹脂 Bu 銅/亜鉛アクリル樹脂 シリルアクリル樹脂 C=O C=O C=O O O O Sn Bu Bu Me O C=O R M Me: C or Zn Cu Z 165 R Si R R 各種錫フリー船底塗料の特徴(溶出型) 経時表面変化 塗装直後 加水分解型A/F 水和分解型・ 崩壊型A/F 拡散型A/F (μg/cm2 /day) 防汚剤放出 出速度[Cu u] 60 50 拡散型 (塩化ゴム/ロジン) 40 30 自己研磨型(SPC) 20 10 生物が付着する放出量 が 着 0 2 4 6 8 10 測定期間(月) 図 防汚剤(Cu 2 O)の放出速度 166 12 スズフリー自己研磨型樹脂 (比較的古いタイプの樹脂) 銅アクリル樹脂 亜鉛アクリル樹脂 C=O C=O O O Cu Zn O O C=O C=O R R シリルアクリル樹脂 C=O O iPr Si iPr iPr (当社塗料には使用しておりません) 新規加水分解型樹脂(HyB) シリルアクリル樹脂A/Fの難点を克服するため、従来の 金属含有アクリル樹脂技術 を組み合わせ新規樹脂を開発 銅アクリル樹脂 シリルアクリル樹脂 O Cu O + iPr C=O O O O Si シリル・ 銅アクリル樹脂 C=O C=O C=O ハイブリッド化樹脂 Cu iPr O iPr C=O C=O C O R R 167 iPr Si iPr iPr
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