Unmanned Underwater Surveillance Robot
Mithun Dama and Sabri Tosunoglu
Department of Mechanical and Materials Engineering
Florida International University
10555 West Flagler Street
Miami, Florida 33174
786-303-5029
[email protected]
[email protected]
ABSTRACT
This paper addresses the mechanical design of an unmanned
underwater surveillance robot. The conditions of the working
environment are taken into consideration in the design. The robot
resembles the shape of a torpedo or missile and has a propeller in
the rear along with the fins to help its flexible motion. The robot
is designed to weigh 100 kg, dive to a depth of 500 m, and
achieve speeds of 4 m/s. Various sensors are being tested to assist
the robot with navigation. A camera is mounted on the top of the
robot in order to have a 360-degree view of the surroundings.
GPS tracking system is used to remotely track the location of the
robot. Structural analysis is carried out using SolidWorks, and the
initial results have been satisfactory. Optimal robot design
parameters have also been determined for the optimal
performance of the robot.
In fact, the first Autonomous Underwater Vehicles (AUVs) were
developed during the 60s and 70s with the SPURV (SelfPropelled Underwater Research Vehicle, USA) and the Epaulard
(France). SPURV displaced 480 kg, and could operate at 2.2 m/s
for 5.5 hours at depths to 3 km.
Keywords
Surveillance, AUV, RUV, Propeller, Fins and Hull.
1. BACKGROUND
The ocean covers about 71% of the earth’s surface and years of
research and exploitation shows mankind’s ignorance and the
difficulties we have in using this primordial and generous
environment. Fortunately, this mysterious element has generated
an unquenchable curiosity that pushed people like Le Prieur,
Cousteau, Piccard, Walsh, and many others, to accomplish what
was considered as impossible.
In 1531, Guglielmo de Lorena dived on two of Caligula's sunken
galleys using a diving bell based on a design by Leonardo da
Vinci. In 1776 David Brushnell invented the Turtle, the first
submarine to attack a surface vessel, starting the long story of
underwater warfare.
In 1960, Jacques Piccard and Lt. Don Walsh touched the deepest
point in the Mariana Trench (10,916 m) onboard the bathyscaphe
Trieste, and confirmed that life was everywhere. Navies were the
first to show their interest in developing unmanned marine
systems. In 1866, the Austrian Navy asked Robert Whitehead to
develop a new weapon for warships. He demonstrated the
efficiency of a self-propelled floating device, carrying an
offensive payload [2]. The torpedo vehicle class was then born.
2011 Florida Conference on Recent Advances in Robotics
Figure 1. Halley’s Diving Bell, Late 17th Century.
Weighted Barrels of Air Replenished the Bells
Atmosphere.
Figure 2. Prototype of Epaulard.
The vehicle was acoustically controlled from the surface and
could autonomously run at a constant pressure, perform see-saw
action between two depths, or climb and dive at up to 50 degrees.
Researchers used the vehicle to make conductivity and
temperature measurements along isobaric lines in support of
internal wave modeling (Ewart, 1976). Submersible Epaulard was
Gainesville, FL, 4-5 May 2011
3 tons in weight and could operate by depth of 6,000 meters for
up to 7 hours and maintain a velocity of around 1 knot. An Ultra
short Base Line (USBL) allowed for uploading orders and
positioning relative to the mother ship (IOC UNESCO, 1985).
These systems were the forerunners of over 2,400 inhabited
undersea vehicles presently in regular operation worldwide [12].
2. PROJECT MOTIVATION
There have been many latest developments in the field of
unmanned underwater vehicles in order to reveal the secrets of the
deep seas which are left untouched due to many constraints and
also to reduce human fatality during this process. The unmanned
underwater vehicles should have a means of motion which comes
in the form of propellers or fins. There are many robots which use
either propellers or fins and have considerably less diving depths.
This motivated developing a system to improve (1) the driving
mechanisms to achieve smoother and efficient motion of the
vehicle, and also (2) increasing the diving depths of the robot.
of the robot is expected to be about 100 kg and it is expected to
dive up to 500 meters withstanding all real time situations. The
speed of propulsion may range from 2 to 4 m/s as we use both
propellers and also fins for the locomotion of the robot. AISI
1020 steel alloy is used to build the hull of the robot and various
rubbers are being tested to optimally build the fins of the robot. At
depths of 300 to 500 m in the sea, the pressure experienced by the
robot is 30.7611 to 50.6019 atm, respectively.
4.1 Specifications
Specifications of the unmanned underwater surveillance robot
such as its dimensions, weight, payload, material used for the
manufacturing of the robot and the speed with which the robot is
designed to propagate through the workspace are summarized
below.
Length x Width x Height: 2 m x 0.3 m x 0.3 m
Weight: 100 kg
Operating Depth: Up to 500 m
3. INTRODUCTION
Working Pressure: 30.7611 to 50.6019 atm
There are two different types of unmanned underwater robots.
They are ROV (Remotely Operated Vehicle) and AUV
(Autonomous Underwater Vehicle). The ROVs are remotely
operated by wire or tether connections. They are mostly frame
shaped and are applicable to works done at lesser depths. The
AUVs work on inbuilt programs and communicate to the operator
with the help of sensors. They are powered by capacitor batteries
or fuel cells based on the requirement. Autonomous underwater
vehicles (AUVs) are submersibles with the ability to operate and
carryout missions without manual inputs. They appeal to the
community in that they are able to operate using their own power
supply, make decisions according to the input from the onboard
sensors and provide data storage capabilities [1].
Material used to build the body: AISI 1020
There are certain basic needs that must be fulfilled which lead to
the invention of the unmanned marine vehicles. They are
intelligence, surveillance, reconnaissance, mine countermeasures,
anti-submarine
warfare,
inspection
and
identification,
oceanography, communication/navigation network nodes, payload
delivery, information operations, and time critical strike. In the
current work, mechanical design of an autonomous underwater
vehicle is addressed to accomplish some of these needs.
The robot has a shape of torpedo with a propeller and fins to
allow its motion, sensors to guide it through the path, night vision
camera to enable the robot to take pictures of its surroundings
clearly even with less light, and GPS system to track its location.
The mechanical design includes design of a propeller, fins, and
the body of the robot. DC-motors are used to provide the
sufficient torque to the fins and propeller. The size of the robot is
2 m x 0.3 m x 0.3 m, and weighs approximately 100 kg. The
major goals that are set in the design of the robot are:
Fins: Rubber
Operational Speed: 2 to 4 m/s
Figure 3. Conceptual Design of the Unmanned Underwater
Robot.
1. To withstand and work at a given working environment
which includes depths of up to 500 m.
2. To be reliable.
3.
To allow easy maintenance.
Figure 4. The Dimensions of the Robot’s Hull.
4. ROBOT CONFIGURATION
The unmanned underwater vehicle that is designed is 2 m in
length, 0.3 m in width and 0.3 m in height. The maximum weight
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4.2 Design Considerations
The unmanned underwater surveillance robot is 2 m in length and
0.3 m in both width and height. The thickness of the pressure hull
is 49.3 mm. The robot dimensions are selected to have these
values to accommodate the motors which are used to give the
waving motion to the fins and also to drive the propeller shaft,
sensors that help the robot to navigate and communicate with the
surroundings and the base. The battery is the life source of the
robot and the microprocessor is the brain of the robot and empty
space is allocated to accommodate pay load.
These design parameters are used to develop a SolidWorks model
which has been structurally analyzed. The following unit
conversions are used in the SolidWorks software.
Figure 5. The Forces at Work in Buoyancy.
•
1 m = 39.37 in
•
1 psi = 6894.75729 Pa
5.1.1.1 Equation for Archimedes Principle
•
1 atm = 14.696 psi
The Archimedes Principle is represented by the following
equation:
•
1 Pa = 1 N/m
•
1 kg = 2.2 lbs
2
4.3 Power Source
The buoyancy of a submerged body =
Weight of displaced liquid – Weight of the body
Based on the space constraints and the capacity of the motors
used, either fuel cell or lithium ion batteries are to be used and
based on the constraints such as payload, working environment,
torque, etc., the capacity of the motors will be decided. Overall,
there will be five motors mounted on the robot among which four
will be used to operate the fins and one will be used for the
propeller.
From this equation, we can conclude that the body will float if the
buoyancy is positive, the body will sink if the buoyancy is
negative, or the body will be stuck if the buoyancy is neutral.
The buoyant force of a liquid depends on its density, its weight
per unit volume. The density of freshwater is 62.4 pounds per
cubic foot (28.3 kg/ 0.03 m3) and the density of seawater is 64
pounds per cubic foot (29 kg/0.03 m3) which is denser than
freshwater.
4.4 Sensors
6. MATERIAL SELECTION
One of the major challenges in developing the vehicle autonomy
is the availability of the sensory system for guidance and
navigation. Various sensors to support the vehicle mission will be
tested and integrated into the vehicle system. The investigation
will include optical and acoustic imaging for inspection; sonar
inertial system and gyroscope for navigation; sonar,
magnetometer, laser scanner, magnetic scanner and chemical
scanner for recovery; and force, tactile and proximity sensors for
construction.
The material selection should be done with most care as the
properties of the material determine the strength of the robot and
thus directly affects to the success of the final product. While
selecting the material, some crucial factors such as operating
environment, payload, life expectancy, the type of stresses and
strains induced due to the payload and the liquid are taken into
account.
5. MECHANICAL DESIGN
Table 1 summarizes properties of the material used for building
the robot. The selected material is AISI 1020, which also exists in
the SolidWorks materials library and also is a linearly elastic and
isotropic material.
The design mainly involves two major parts. The hull and the fins.
The hull is like the skull to the human body which protects the dry
parts inside it from getting wet. The hull should be designed in
such a way that it withstands the pressure of the depths. The hull
is of cylindrical shape providing higher structural integrity [9].
The fins are designed based on the fin structure of the fish.
5.1 Factors that Affect Unmanned
Underwater Vehicle
5.1.1 Buoyancy
Archimedes states that any body completely or partially
submerged in a fluid (gas or liquid) at rest is acted upon by an
upward (buoyant) force, the magnitude of which is equal to the
weight of the fluid displaced by the body.
2011 Florida Conference on Recent Advances in Robotics
6.1 General Description
Table 1. General Description of the Material.
Material name
AISI 1020
Material Source
Library files
Material Library Name
SolidWorks materials
Material Model Type
Linear elastic isotropic
6.2 Properties of AISI 1020
Of all the different steels, those produced in the greatest quantities
fall within the low-carbon classification. These generally contain
less than about 0.25 wt%C and are unresponsive to the heat
treatments intended to the form martensite; strengthening is
Gainesville, FL, 4-5 May 2011
accomplished by cold treatment. Microstructure of AISI 1020
consists of ferrite and pearlite constituents. They have outstanding
ductility and toughness; in addition, they are machinable,
weldable, and of all steels, are the least expensive to produce. The
most common metal used to build submarines is high strength
steel alloy. Due to its low cost and availability, AISI 1020 is used
for the first prototype construction and preliminary testing.
Table 2. Material Properties of AISI 1020.
Property Name
Value
Units
Elastic modulus
2.9008e+07
Psi
Poisson's ratio
0.29
NA
Shear modulus
1.1168e+07
psi
Mass density
0.28541
lb/in^3
Tensile strength
60989
psi
Yield strength
50991
psi
8.3333e-06
1/Fahrenheit
0.00062861
BTU/(in.s.F)
0.10033
Btu/(lb.F)
Thermal expansion
coefficient
Thermal
conductivity
Specific heat
In order to increase depth, certain parameters such as size, weight
and speed variations have to be compromised.
7. FLOW SIMULATIONS
The initial design of the autonomous underwater robot that can
reach depths of 500 m and run at 4 m/s speed was developed in
the SolidWorks platform which led to the CFD and structural
analyses. Many factors are taken into consideration to develop
flow simulations in Cosmos FloWorks, which also helped us to
optimize design parameters.
Figure 6. Isometric View of the Rectangular Design.
Figure 7. Isometric View of the Torpedo Design.
7.2 Pressure Profile Comparison between
Rectangular and Torpedo Designs
The comparison of the two shapes is accomplished using Cosmos
FloWorks module of SolidWorks. Figures 8 and 9 illustrate the
results of pressure profile over the rectangular and torpedo
profiles, respectively. The minimum and maximum pressures
acting on the rectangular design are 92,357.6 Pa and 106,971 Pa,
respectively. The minimum and maximum pressures acting on the
torpedo design are 94,362.1 Pa and 115,057.0 Pa respectively.
7.1 3D Representation of Rectangular and
Torpedo Designs
There are many shapes of unmanned underwater robots that can
be used for comparison but considering the majority, rectangular
design and torpedo design have been chosen to compete for the
best streamline design. This section discusses in detail the results
of pressure, velocity, and velocity in the direction of flow results
between these two designs (torpedo and rectangular hull profiles).
Figures 6 and 7 show the 3D representation of both rectangular
and torpedo design which are used in the velocity as well as in the
structural analysis.
Figure 8. Pressure Acting over the Rectangular Design.
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10 indicates the pressure distribution in the torpedo design and
Series-1 line in the same figure indicates the pressure distribution
in the rectangular design. The mesh is refined to obtain the
optimum result.
7.3 Velocity Comparison between
Rectangular and Torpedo Designs
Figure 9. Pressure Acting over the Torpedo Design.
The comparison of the two shapes is carried out using Cosmos
FloWorks module of the SolidWorks package. Figures 11 and 12
depict the results of velocity variation over the rectangular and
torpedo designs, respectively. The minimum and maximum
velocities over the rectangular design are 0.458411 m/s and
4.58411 m/s, respectively. The minimum and maximum velocities
over the torpedo design are 0.493902 m/s and 4.93902 m/s,
respectively.
Table 3. Overall Pressure Distribution over the Two Sections.
Pressure of Rectangular
Pressure of Torpedo
Design [Series-1] (Pa)
Design [Series-2] (Pa)
92357.6
94362.1
93981.3
96661.6
95605
98961.1
97228.7
101261
98852.4
103560
100476
105860
102100
108158
103723
110458
105347
112758
106971
115057
Figure 11. Velocity Distribution over the Rectangular Design.
Figure 12. Velocity Distribution over the Torpedo Design.
Figure 10. Line Chart Showing the Pressure Distribution.
Table 3 shows the comparison of pressure distribution in
rectangular and torpedo designs. By studying Figure 10 and Table
3, we can see that the torpedo design is able to handle far higher
pressures than the rectangular design. The Series-2 line in Figure
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Table 4 provides a comparison of velocity variations in
rectangular and torpedo designs. By referring to the graph in
Figure 13, we can see that the torpedo design reaches higher
velocities than the rectangular design, which is an indication of
better streamline shape of the torpedo profile. The Series-2 line in
Figure 13 indicates the velocity variation in the torpedo design
and the Series-1 line in the same figure indicates the velocity
variation in the rectangular design. The mesh is refined to obtain
the optimum result.
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Table 4. Velocity Variation over the Two Surfaces.
Velocity over Rectangular
Velocity over Torpedo
Design Series-1 (m/s)
Design Series-2 (m/s)
0
0
0.458411
0.493902
0.916821
0.987804
1.37523
1.48171
1.83364
1.97561
2.29205
2.46951
2.75046
2.96341
3.20887
3.45732
3.66729
3.95122
4.1257
4.44512
4.58411
4.93902
Figure 14. Velocity Component in the Direction of Flow on
Rectangular Design.
Figure 15. Velocity Component in the Direction of Flow on
Torpedo Design.
Table 5. Variation of Velocity in the Direction of Flow of
Liquid Over Rectangular and Torpedo Designs.
Figure 13. Line Chart Showing the Velocity Variations in the
Two Designs.
Velocity Component in the
Direction of Flow,
Rectangular Design
Series-1(m/s)
Velocity Component in
the Direction of Flow,
Torpedo Design
Series-2(m/s)
1.29803
1.61681
0.717117
0.962966
0.136199
0.309622
The comparison of the two shapes is done using cosmos flow
works in solid works software. Figure 14 and 15 illustrate the
results of velocity variation in the direction of flow over the
rectangular and torpedo designs respectively.
0.444718
0.343722
1.02564
0.997067
1.60655
1.65041
The minimum and maximum velocities over the rectangular
design are 1.29803 m/s and 4.51114 m/s, respectively whereas the
minimum and maximum velocities over the torpedo design are
1.61681 m/s and 4.91713 m/s, respectively.
2.18747
2.30376
2.76839
2.9571
3.34931
3.61044
3.93022
4.26379
4.51114
4.91713
7.4 Comparisons of Velocity Component in
the Direction of Flow between Rectangular
and Torpedo Designs
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Table 6. Maximum and Minimum Values of the Von Mises
Stress, Strain and Displacement.
Type
Min
Max
Stress
Name
VON. von
Mises Stress
1.12608
N/m^2
Node. 11055
3.08174e+007
N/m^2
Node. 4949
Displacement1
URES.
Resultant
Displacement
0 mm
0.034685 mm
Node. 214
Node. 7541
ESTRN.
Equivalent
Strain
4.96E-12
0.000107603
Element.
4470
Element. 1051
Strain1
Figure 16. Line Chart Showing the Velocity Variation in the
Direction of Flow of Liquid.
Table 5 shows the comparison of velocity variations in the
direction of flow in rectangular and torpedo designs. By studying
the results portrayed in Figure 16, we see that the torpedo design
reaches higher velocities than the rectangular design which is an
indication of better streamline shape of the torpedo.
The Series-2 in Figure 16 indicates the velocity variation in the
torpedo design and Series-1 line in the same figure indicates the
velocity variation in the rectangular design. The mesh is refined to
determine the optimum result.
7.5 Structural Analysis of the Rectangular
Design
The static analysis is accomplished on the hull of the rectangular
design to determine the stress, strain and displacement of the hull
under uniform load of 710.264 psi which is the pressure that the
hull is going to experience near the depths of 500 m in the sea.
Table 6 lists the minimum and maximum values of stress, strain
and displacement along with their point of accurance. Figures 17,
18 and 19 illustrate the simulation of the above listed entities.
Figure 17. Simulation of von Mises Stress.
The minimum and maximum values of the von Mises stress are
1.12608 N/m2 and 3.08174e+007 N/m2, respectively. The
minimum and maximum values of the displacement are 0 mm and
0.034685 mm, and the minimum and maximum values of the
strain are 4.96E-12 and 0.000107603.
The static analysis is done by applying fixed restraints on both
sides of the hull and applying normal pressure uniformly on all
four faces of the hull.
7.6 Structural Analysis of the Torpedo Design
The static analysis is carried out on the hull of the torpedo design
to determine the stress, strain and displacement of the hull under
uniform load of 710.264 psi which is the pressure that the hull is
going to experience near the depths of 500 m in the sea. Table 7
shows the minimum and maximum values of stress, strain and
displacement.
Figure 18. Simulation of Displacement.
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Figure 20. Simulation of von Mises Stress.
Figure 19. Simulation of Strain.
Figures 20, 21 and 22 show the simulation of the above listed
entities. The minimum and maximum values of the von Mises
stress are 16.1208 N/m2 and 5.92956e+06 N/m2, respectively. The
minimum and maximum values of the displacement are 0 mm and
0.000774556 mm and the minimum and maximum values of the
strain are 1.35E-10 and 2.23E-05. The static analysis is obtained
by applying fixed restraints on both sides of the hull and applying
normal pressure uniformly on all four faces of the hull.
Table 7. Maximum and Minimum Values of the Von Mises
Stress, Strain and Displacement.
Name
Stress1
Displacement1
Strain1
Type
VON. von
Mises Stress
URES.
Resultant
Displacement
ESTRN.
Equivalent
Strain
Min
Max
16.1208
N/m^2
5.92956e+06
N/m^2
Node. 24122
Node. 86
0 mm
0.000774556
mm
Node. 78
Node. 2698
1.35E-10
Element. 6757
Figure 21. Simulation of Displacement.
2.23E-05
Element. 9973
Figure 22. Simulation of Strain.
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8. CONCLUSION
The initial mechanical design of the unmanned underwater
surveillance robot is addressed to meet the 500-m depth and 4 m/s
velocity goals. Two different hull shapes, namely, rectangular and
torpedo profiles are considered in this study, and the performance
of each profile is studied in terms of pressure and velocity
distributions. Comparative studies showed that the torpedo profile
was a more promising design alternative. Static analysis is also
presented to check the stability of the robot’s hull and the results
are tabulated. Future work involves the construction of a
prototype based on the mechanical design presented in this work.
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2011 Florida Conference on Recent Advances in Robotics
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