International Journal of Engineering Trends and Technology (IJETT) – Volume 38 Number 5- August 2016
Case Study on Effect of Static and Dynamic
Loads on Hyperboloid Shell Structure
Sithara T1, Ance Mathew 2
Department of Civil Engineering, St. Joseph College of Engineering and Technology, MG University
Kottayam, Kerela, India
Abstract—
Hyperbolic
structures
have
a
negative Gaussian curvature, meaning they curve
inward rather than outward or being straight. This
paper deals with the static and dynamic analysis of
existing cooling tower of 143.50m high above ground
level. The existing cooling tower is chosen from
Bellary thermal power station . These cooling towers
have been analyzed for self weight, wind loads and
seismic loads and using ANSYS software. Two
analysis methods done and compared were Time
history and Response spectrum .
Keywords: cooling tower, ANSYS software, Time
history, response spectrum.
I. INTRODUCTION
Hyperboloid
structures are architectural
structures designed using a hyperboloid in one sheet.
Often these are large structures such as towers where
the hyperboloid geometry's structural strength is used
to support an object high off the ground, but
hyperboloid shape is also often used for adorning
effect as well as structural economy. With cooling
towers, a hyperbolic structure is considered. At the
bottom, the enlarging of the tower provides a large
area for installation of fill to promote thin film
evaporative cooling of the circulated water. As the
water first evaporates and rises, the narrowing effect
helps accelerate the laminar flow, and then as it
widens out, contact between the heated air and
atmospheric air supports turbulent mixing. .Natural
draught hyperbolic cooling towers are the important
structures of a power station. They contribute both to
an efficient energy output & to a careful balance with
our environment. These structures are most efficient
measures for cooling thermal power plants by
minimizing the need of water & avoiding thermal
pollution of water bodies. This paper included the
study of static and dynamic analysis of hyperbolic
cooling tower (i.e. self weight, seismic load, wind
load).
In this study analysis and modelling were done
using software. Two analysis methods done and
compared were Time history and Response spectrum .
II. HYPERBOLOID STRUCTURE
Hyperbolic structures have a negative Gaussian
curvature, meaning they curve inward rather than
outward or being straight. As doubly ruled surfaces,
This means that the structure is curved in 2 directions
ISSN: 2231-5381
which are generated by using only straight members.
Today the most common application of hyperboloid
structures is for power station cooling towers, where
the shape permits a minimum thickness of the
concrete shell and a boost to the cooling airflow due to
the Venturi effect of the cross-section.
III GEOMETRY
Total height (H)
: 143.5 m
Height of throat (Hthr)
: 107.75m
Diameter at top (Dt)
: 63.7 m
Diameter at bottom (Db)
: 110 m
Diameter at throat level(Dthr)
: 61 m
IV ANSYS MODEL
The finite element analysis adopted by ANSYS
Work Bench version 16 was used.Shell was modeled
using shell 181 element.
Then the meshing is done to desctritize the model .
For meshing grid independence study was done.
http://www.ijettjournal.org
Page 233
International Journal of Engineering Trends and Technology (IJETT) – Volume 38 Number 5- August 2016
Fig 2 Maximum principal stress
From the mesh convergence study we can conclude
that after testing the model with element size of
2000mm, 1800mm, 1600mm, 1200mm, 1000mm and
800mm, the results obtained are more similar after
1200mm and with very less margin of error for the
parameter taken for mesh convergence study.Thus we
can take 1200mm as element size for all study. After
meshing boundary conditions and loads are applied.
IV MATERIAL PROPERTIES
Young modulus
: 31GPa
Poisson ratio
: 0.15
Density of RCC
25KN/m^3
V ANALYSIS RESULTS
A.
Fig 3 Vonmises stress
B . Modal analysis
Static analysis
Fig 4 Natural frequencies obtained
Fig 1 Total deformation
Fig 5 Total deformation (mode 1)
ISSN: 2231-5381
http://www.ijettjournal.org
Page 234
International Journal of Engineering Trends and Technology (IJETT) – Volume 38 Number 5- August 2016
C. Buckling analysis
Fig 10 Minimum principal stress
E. Seismic analysis
Fig 6 Total deformation
D. Wind analysis
1). Time history analysis
Here in this analysis we took an acceleration vs
time of a live earth quake data. Due to computational
limitations we took the analysis time as 12 sec since
maximum acceleration plotted is during first 12 secs.
Fig 7 Total deformation
Fig 11 Total deformation
Fig 8 Vonmises stress
Fig 12 time vs deformation
Fig 9 Maxmum shear stress
Fig 13 Directional deformation (x axis)
ISSN: 2231-5381
http://www.ijettjournal.org
Page 235
International Journal of Engineering Trends and Technology (IJETT) – Volume 38 Number 5- August 2016
Fig 18 Maximum shear stress
Fig 14 Directional deformation (y axis)
Fig 19 Maximum principal stress
Fig 15 Directional deformation(z axis)
VI . CONCLUSION
From the analysis conducted on the cooling
tower using both method, there are enough result
differences which can substantiate that transient
dynamic analysis is better in capturing accurate result.
Some noted points are below,
•
Transient analysis accounts for post failure
condition whereas in response spectrum it is
not possible.
•
In transient dynamic analysis we can capture
the seismic failure over the period of seismic
event.
•
In transient analysis we can account for its
structural damping conditions, where as in
response spectrum it is not possible.
•
In transient dynamic analysis we account for
its structural Non-linearity such as material
non-linearity, Large deformation etc.
Fig 16 Maximum principal stress
2) Response spectrum analysis
A response-spectrum analysis helps to find out the
maximum response of a structure to a transient load. It
is used as a fast alternative of approximating a full
transient solution. The maximum response is
computed as scale factor times the mode shape. These
maximum responses are then integrated to calculate
the total response.
From these noted point we can conclude that transient
dynamic analysis is much better than response
spectrum analysis to accurately predict the seismic
event.
REFERENCES
[1]
[2]
P C Bamu and A Zingoni , ―Damage , deterioration and the
lon– term structural performance cooling tower shells : A
survey of developments over the past 50 years”,Engineering
structures 27 1794-1800 june ,2005
A. M. El Ansary, A. A. El Damatty, and A. O. Nassef,
―Optimum
Fig 17 Total deformation
[3]
shape and design of cooling towers” World
academy of science,Engineerong and technology 2011
G. Murali, C. M. Vivek Vardhan and B. V. Prasanth Kumar
Reddy
ISSN: 2231-5381
―Response of cooling towers to wind load‖,
http://www.ijettjournal.org
ARPN
Page 236
International Journal of Engineering Trends and Technology (IJETT) – Volume 38 Number 5- August 2016
Journal of Engineering and Applied Sciences, VOL. 7, NO. 1,
JANUARY 2012 ISSN 1819-6608
[4] N Veena, and M. U Aswath, Sayeed Sulaiman “ comparative
study of the effect of seismic and wind loads on the cooling
towers with A frame and H frame column support”, The
International Journal Of Science & Technoledge (ISSN 2321 –
919X), Vol 1 Issue 2, August, 2013
[5] Sachin Kulkarni ―Wind and Buckling Analysis of Natural
Draught Cooling towers using ANSYS” , ISRASE First
International Conference on Recent Advances in Science &
Engineering ,2014
[6] Tejas G. Gaikwad, N. G. Gore, V. G. Sayagavi “Effect of
Wind Loading on Analysis of NaturalDraught Hyperbolic
Cooling Tower‖, International Journal of Engineering and
Advanced Technology (IJEAT) ISSN: 2249 – 8958, Volume-4
Issue-1, October 2014
[7] Parth.R.Chhaya, Nizam.M.Mistry, Anuj.K.Chandiwala ― A
review on effect of wind loading on natural draught
hyperbolic cooling tower‖ , International journal of advance
engineering and research development Volume 1,Issue 12,
December 2014
[8] Ali I. Karakas, Ayse T. Daloglu, ―Free and Forced Vibration
Analyses of Hyperbolic Cooling Tower ShellUsing Harmonic
Solid Ring Finite Elements‖, Journal of Engineering and
FundamentalsVol. 2(1), pp. 38-53, June 2015
[9] Akhil Nema, K. K. Pathak, ―Parametric Earthquake Analysis
of Natural Draught Hyperbolic Cooling Tower‖ International
Journal of Engineering Research Volume No.5, Issue Special
1 pp : 143-148 Jan 2016.
[10] Pushpa B. S, Vasant Vaze,and P. T. Nimbalkar, ―Performance
Evaluation of Cooling Tower in Thermal Power Plant - A
Case Study of RTPS,Karnataka‖, International Journal of
Engineering and Advanced Technology (IJEAT)ISSN: 2249 –
8958, Volume-4 Issue-2, December 2014
ISSN: 2231-5381
http://www.ijettjournal.org
Page 237