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INTRODUCTION
What is an AUV?
Autonomous Underwater Vehicle (AUV) is an underwater robotic system, which
unlike a Remotely Operated Vehicle (ROV) does not have any direct physical link
with any other system either on the surface or elsewhere. The main purpose of an
AUV is to carry payload, which will enable it to carry out a specific task. The
configuration of AUV along with payload will depend on mission’s requirements. The
payloads are in general are various instruments which carry out survey of specific
sites in the ocean or measure ocean water characteristics, survey/inspection of
installations such as, underwater pipelines or offshore structures.
Unstructured oceanic environments present great challenges to AUV navigation.
However, with continual improvements in sensor technology, new methods of
navigating in the hazardous underwater terrain are far more effective than ever
before. Autonomous underwater vehicles are currently being utilized for scientific,
commercial and military underwater applications. These vehicles require
autonomous guidance and control systems in order to perform underwater tasks.
Modelling, system identification and control of these vehicles are still major active
areas of research and development.
HISTORY:
The first AUV was developed at the Applied Physics Laboratory at the University of
Washington as early as 1957 by Stan Murphy, Bob Francois, and later on Terry
Ewart. THE SPECIAL PURPOSE UNDERWATER RESEARCH or (SPURV), was
used to study diffusion, acoustic transmission and submarine wakes.
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.
Fig. ORCA IX
Second design we took into account was the "Subjugator” being developed at the
University of Florida. Five thrusters provide motion. A Pentium embedded single
board performs its vision system and Atmel AVR micro controllers manage sensors
and actuators. These micro-controllers make higher-level decisions and control
analogue and timing related interfaces. This AUV won the 2005 AUVSI competition.
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Fig. Subjugator
Fig. Mako
Third design which caught our eyes was The “Mako” which is the first AUV of the
University of Western Australia developed in 2004 at the Mobile Robotics Lab of
CIPPS. It has a strongly symmetric design with two vertical thrusters for heave
motion and two thrusters attached on the sides for surge and yaw motion. Recent
research on the AUV deals with motion control and the sensor suite.
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Fig. Tethys
Finally we also took the help from the recent model of Tethys presented by J.G.
Bellingham et al. (2010). It is a Small, Long-Range AUV with Flexible Speed and
Payload travelling around 1,000 kilometres at one meter per second weighing about
120 kilograms with 8 sensor watt payload. Buoyancy driven vehicles or Gliders are
designed to carry a minimal sensor suite for as long as possible and challenged by
currents and limited payload capacity. It has a new feature of drift capability.
PROJECT MOTIVATION
The outcome of this project should be a small, highly transportable and high
performance AUV, constructed to participate in AUV competitions and to provide
groundwork for future research.
The objectives of this project were:
Design of the electronic system, which provides:
Motion control
Energy control and recharge
Communication
Easy and reliable design
All controller values soft coded for easy modifications
Failsafe connectors
Choose, build up and calibrate the sensor suite including:
Navigation sensors: for sensing the motion of the vehicle
Mission sensors: for sensing the operating environment.
*Implement a controller system for controlling, tracking and navigation of the AUV.
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CONCEPT DEVELOPMENT
Our AUV “JAL NETRA” resembles a capsule having its own power, propulsion,
navigation and control systems. Torpedo like structure was thought to be chosen for
Jal Netra 3.0 as torpedo shape is the most tried and trusted shape in the field of
underwater robotics. The idea which gave birth to AUV JAL NETRA was the idea of
making a torpedo shaped AUV but without the drawbacks of a conventional torpedo
models which ultimately lead us to capsule like structure. The primary drawbacks
which we were trying to overcome were the torpedo shape’s inability to hover, its
huge turning radius and stability issues, while maintaining the original plus points of
optimum speed & lowest possible drag. The ideal minimum drag laminar flow design
is not favourable as the curved shape does not facilitate the optimum placement of
equipment and thereby disallowing the full use of the obtained buoyancy. Other
objectives included making the AUV as compact as possible using the latest cutting
edge technology keeping all the equipment to its optimum working performance. And
lastly keeping the AUV as cost effective as possible making it economically as well
as scientifically viable. The primary objectives of this conceptual design were near
surface surveillance (up to 25mts depth) and capacity of sensing temperature,
Conductivity (salinity) and providing visual information at a specified depth.
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1. Shape & Size
The hydrodynamic form of an AUV minimizes the propulsion energy requirement, as
well as stability and manoeuvrability ay various operating speed. A hull form may
also impose limitations on vehicle access, launch and recovery, and maintenance.
Specifically the following considerations are important in selecting a hull form.
a) Minimization of overall drag.
b) Minimization of flow separation.
c) Stability of the sensor platform at nominal forward speed
d) Stability and manoeuvrability at lower speeds of the order 1m/s.
Fig shows the shape of a
typical laminar flow hull. The
main disadvantage of this
unique shape is that it does
not readily permit
lengthening or shortening of
the vehicle thus limiting the
possibility of modular expansion. A simpler alternative to the laminar flow form is the
capsule shaped apart from torpedo shaped body.
1.1. CHOOSING THE FINAL DESIGN
A capsule shape was chosen for the final design because of its significant
advantages over the other proposed designs.
The capsule design provided the following:
Least possible drag
The multi-section design facilitates the easy assembly and dismantling which
is problem in a conventional torpedo model
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High modularity due to the relative ease with which components can be
attached to the skeletal frame
Cost-effectiveness because of the availability and use of common materials
and components
The movable frame makes the fitting and removing of equipment relatively
easy.
Ease in submerging with perfectly balanced buoyancy
Static stability due to separation of the centres of mass and buoyancy and
dynamic stability due to centres of gravity and buoyancy being in same
vertical plane and centre of drag is easily identifiable
Substantial internal space due to small equipment arranged properly in a
space which is perfectly hydrodynamic from the outside, thereby making the
AUV as compact as possible.
The hemispherical shape was selected for the head and tail because the
sphere is the shape which has the least amount of surface area for the given
value of containment volume.
Precision in controlling the vehicle and overall simplicity along with speed and
sleekness both are taken care of in mechanical design of JALNETRA.
1.2. MECHANICAL SYSTEM DESIGN:
The mechanical system of the JALNETRA sought to fulfil the following main
objectives:
To be as compact as possible.
To provide a dry, watertight hull that facilitates the housing of on board
electronic components and that is capable of surviving in a saltwater
environment and easily available for maintenance.
To provide a static and dynamically stable vehicle with suitable versatility in its
motion to accomplish a wide range of tasks and is having 4 degrees of
freedom.
To possess the ability to be modular, extensible and versatile for future
missions of varying nature.
Light construction, easy to transport
Connectors through the hull for recharging and sensors
SPECIFICATIONS OF BODY DIMENSIONS (cm)
Length Overall (with frame & outer equipment ) 110
Length of Pressure Vessel 62
Length of the Cylindrical Mid body 40
Outer Dia. Of pressure vessel 22
Inner Dia. Of pressure vessel 20
Outer Diameter of Head/Tail Hemisphere 22
Inner Diameter of Head/Tail Hemisphere 20
Plate Thickness 01
Diameter with extruded portion 27
Width of extruded portion over hemisphere 1.4
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DIAGRAM: ALL 2D VIEWS OF AUV JALNETRA WITH DIMENSIONS & 1 3D VIEW SNAPSHOT
2. WEIGHT
It includes
The hull (dependent on the material density)
The navigational components
Sensory equipment
Electrical hardware and circuitry
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In AUV, weight is a deciding factor for the cost and power requirement of the AUV. In
AUV JALNETRA all these factors have been taken into account to make it a cost
effective, compact and light weight working model. The conclusion has been made
after comparing several models of the working AUVs.
WEIGHT SPECIFICATIONS WEIGHT
(Kg)
Main Pressure Hull 8.0
Outer Frame 11.5
Thrusters 2.82
CTD Sensor 0.95
Heading sensor 0.058
URF 0.008
DVL 0.205
Batteries 0.8
Camera 0.012
Torch 0.048
Motherboards and Electrical
Circuitry
0.252
Torpedo Launcher/ Marker
Dropper
0.5
TOTAL 25.15 Kg
3. TYPE OF BUOYANCY
The magnitude of the buoyant force, B, exerted on a body, floating or submerged, is
equal to the weight of the volume of water displaced by that body. The ability of an
object to float depends on whether or not the magnitude of the weight of the body,
W, is greater than the buoyant force. Clearly, if B > W, then the body will float, while
if B < W it will sink. If B and W equate, then the body remains where it is.
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3.1. THE THREE TYPES OF BUOYANCY:
1) Positive buoyancy (buoyancy > weight)
2) Neutral buoyancy (buoyancy = weight)
3) Negative buoyancy (buoyancy < weight)
The type of buoyancy we are applying in our AUV is Neutral Buoyancy. That is the
weight is equal to the buoyancy.
3.2. SCOPE OF FUTURE DEVELOPMENT IN FAIL-SAFE MECHANISM:
The Air bag system principle can be applied in case of damage and flooding, which
will cause the airbag to inflate as soon as any damage is sensed giving much more
buoyancy than required to pull AUV out of the water.
4. BASIC VEHICLE FRAME DESIGN AND MATERIAL SELECTION
CRITERIA
The frame we have decided for our AUV will be placed around the cylindrical Mid –
Body. The frame we have selected is as shown below in the 3D diagram-
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4.1 FRAME DESIGN SELECTION CRITERIA
1) Easy addition and removal of main hull and external equipment within the frame.
2) Ease of fastening equipment
3) Helps in dismantling the AUV as the entire frame with the equipment can be
detached from the AUV.
4) The material used for frame used is mild steel.
4.1.1. FEATURES OF THE PRESSURE HULL (ASSEMBLY AND DISMANTLING):
4.1.1.1. The Pressure Hull Classification:
a) Hemispherical head
b) Cylindrical parallel mid body
c) Hemispherical tail
4.1.1.2. Procedure of Dismantling the AUV Unit:
a) All the parts of pressure hull and frame are interlocked with each other by bolt and
socket locks.
b) First all the four thruster units are detached from the frame.
c) External equipment like torpedo launcher and marker dropper are dislodged.
18. 18 | P a g e
d) External frame attached with the main pressure hull is unbolted and separated.
e) Now the hemispherical head is detached from the pressure hull.
f) Then the internal frame placed within the parallel mid body is pulled out along with
all the equipment which is placed in it.
g) The components which are passing through the hull are removed at this point
after removing the water proofing.
f) Finally the hemispherical tail can be detached from the mid body.
g) All the bolt and socket locks have rubber coats all around on their perimeter so as
to make all the joints water proof.
i) The assemble process follow the exact reverse path of the process mentioned
above.
4.2. MATERIAL SELECTION CRITERIA:
The next issue of concern was the proper choice of material for the pressure hull. The
pressure to which the AUV is subjected is directly proportional to the depth of operation.
The hull material should thus be strong to withstand this pressure, and should be light in
weight. This means that a material with high strength/weight ratio needs to be
chosen, and it must have suitable material properties for the ease of manufacturing
and other factors.
A number of materials have been explored and the choice made is an
FIBER REINFORCED PLASTIC (FRP). Aluminium alloy of grade Al-7075, Al-7071 or
Al-7175; i.e. an aluminium 7000 series alloy was also considered as an alternative to
FRP. Titanium alloys were considered but due to high cost factor, difficulty in
manufacturing and excess amount of weight and strength for the operational depth led
to the ruling out of that option.
Material Specifications:
General properties Al-7000 series FRP
Ultimate Tensile Strength 572 MPa 1000-1400 MPa
Tensile Yield Strength 503 MPa N/A
Modulus of Elasticity 71.7 GPa 45-56 GPa
Shear Modulus 26.9 GPa 3.5-4.8 GPa
Shear strength 331MPa 100 MPa
Density 2800 kg/m3 2100 Kg/m3
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5. COMPONENT PLACEMENT AND WEIGHT DISTRIBUTION
For our AUV modularity of the shape has been given primary importance. The idea is
to start with a hull form which can be expanded fairly easily as the mission
requirement and consequently the instrumentation leading to larger volume
requirements. Cylindrical shapes are also easier to construct and are structurally
efficient.
Other advantages of this shape include:
a) Better directional stability at low speed
b) Easier launching and retrieval
Given below is the General Arrangement Plan of AUV JALNETRA 3.0-
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Calculation tables are in the EXCEL SHET 1.
These graphs are obtained after the components are placed in the manner as
depicted in the GA Plan as shown in above figure.
The graph given below obtained between difference of mass and buoyancy at every
station.
-5
0
5
10
15
20
25
30
35
40
45
0 0.2 0.4 0.6 0.8 1 1.2
Wt/Buoy.dist.(kg/m)
length of auv(m)
wt/buoyancy distribution Vs Length
bouyacy
mass
-30
-25
-20
-15
-10
-5
0
5
10
0 0.2 0.4 0.6 0.8 1 1.2
load(kg/m) vs length (m)
22. 22 | P a g e
LOAD = WEIGHT – BUOYANCY at any given stations
*NOTE: The areas under the curves of mass and buoyancy don’t exactly match as
we have not taken some negligible auxiliary weights distributed over the length.
Therefore, now the stress is analysed as summation of loads over the length. Hence,
the Bending Stress is calculated by the formulae
S = (Y x M)/ I
Where,
Y = Distance of the Layer In Question From The Neutral Axis
M = Bending Moment
I = Area Moment of Inertia
As all our sections are circular in nature their moment of inertia is given by (πD4)/64
From the above formulas the thickness of the material is finalized at 6mm.Keeping a
Factor of Safety very high as the maximum shear stress bearable by FRP is 100
MPa while the pressure at the depth of 25 m is only 3.5 x 105 Pa (absolute pressure)
with a gauge pressure of 2.5 x 105 Pa. Therefore our AUV with proper change of
instrumentation is able to do deep sea missions as well.
6. CG and CB Calculation
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Assuming no water movement, the stability of a static body underwater is
predominantly affected by the positions of the centres of gravity, CG, and buoyancy,
CB. The centre of buoyancy is the centroid of the volumetric displacement of the
body. If CG and CB are not aligned vertically with each other in either the
longitudinal or lateral directions, then instability will exist due to the creation of a
nonzero moment.
6.1. TRANSVERSE AND LONGITUDINAL STABILITY:
Before an AUV is submerged, considerable effort has been expended, both in design
and operation, to ensure that:
a) The weight of the AUV, with its loads, will be very nearly equal to the weight of the
water it will displace when submerged.
b) The centre of gravity of these weights will be very nearly in the same longitudinal
position as the centre of buoyancy of the submerged AUV.
c) The centre of gravity of these weights will be lower than the centre of buoyancy of the
submerged AUV.
These precautions produce favourable conditions which are described, respectively, as
neutral buoyancy, zero trim and positive stability.
Fig. Transverse Stability
When there is a trimming moment the new equilibrium position is as shown in the figure:
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CG and CB Calculation table is in EXCEL SHEET 2.
CB equal centroid of the displaced volume
Hence, result:
CG Vector transformation:
CGx = 1.345 cm aft of the mid-point
CGy = 0.179 cm from centreline
CGz = 1.857 cm from centreline
CB Vector Transformation:
CBx = 0 cm aft of the mid-point
CBy = 0 cm from centreline
CBz = 6 cm above centreline
.
*NOTE: the CG in the longitudinal direction is 1.345 cm fore of CB which causes a
trimming moment 0.3379 kg-m. And apparent trim in stationary condition 50 approx.
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7. DRAG CALCULATION AND COEFFICIENTS OF DRAG
From the simple perspective of drag reduction a form that promotes laminar flow
within the boundary layer is the best choice. In laminar flow fluid particles move in
layers and skin friction drag is much lower than in turbulent flow where fluid particles
move erratically resulting in high shear stresses between layers. To sustain laminar
flow a hull can be designed such that the diameter increases gradually from the nose
to create a favourable pressure gradient over the forward 60-70% of the hull. In this
area the surface has to be smooth and as hydro dynamically clean as possible. Skin
friction and form drag contribute to the overall vehicle drag. Friction drag varies with
speed and exposed surface area so smaller hulls with smaller surface area have
less friction drag form drag is a function of how well the hull shape minimizes the
flow separation. This component of drag therefore depends upon the shape of the
hull. It is estimated based on the frontal area and is usually larger than the friction
drag for typical AUV configurations. Longer and slender shapes are better for total
drag. Total result show that streamlined form with length and diameter ratios falling
within 5-7 is best in minimizing drag.
7.1. PRESSURE DRAG AND COEFFICIENT OF DRAG (CD):
Some sort of propulsion is required on all AUVs and is usually one of the main
sources of power consumption. Most AUVs use motors for propulsion due to the
scarcity and cost of alternative systems. But, AUV models uses generally thrusters
for movement. The location of the thrusters affects which degrees of freedom can be
controlled. The positioning of the thrusters can also affect noise interference with on
board electronic components, as well as thruster-to-hull and thruster-to-thruster
interactions. Thruster-to-hull and thruster-to-thruster interactions can have unwanted
effects in the dynamics of an AUV.
The drag coefficient is defined as:
Where:
is the drag force, which is by definition the force component in the direction of
the flow velocity
ρ is the mass density of the fluid
is the speed of the object relative to the fluid, and
A is the area normal to the flow.
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Cd= 0.8------ [standard value for pressure drag on a hemispherical surface]
Area normal to the flow: 3.14*R2= 3.14*(0.135)2= 0.057m2
ρ = 1025 kg/m3
V= 1 m/s (design speed)
Therefore substituting the above values in the given equation gives us,
Fd = 23.37 N
7.2. SKIN DRAG AND COEFFICIENT OF
SKIN DRAG (CF):
Reynolds no (Re) = ρ*v*L/(coefficient of
viscosity)
L=overall length of the auv= 1.1 m
CALCULATIONS:
Re= (1025*1*1.1)/900*10-6 = 1.25*106
Re (transition) = 3*106 for all normal
purposes
Therefore the flow type we encounter is
laminar in nature
Re (transition)> Re
Cf (coefficient of skin drag) = 0.664/ Re1/2
=0.664/(1.981*106) ½
=0.5939*10-3
Therefore, Cd=2* Cf = 1.1878*10-3
Thus, drag force is given by
Drag=1.1878*10-3 x 1025 x 1 x (2*surface
area of hemisphere+ surf. ar. of cylinder)/2
=1.1878*10-3 x 1025 x 1x 0.568/ 2
= 0.3457 N
Finally
Total drag = skin drag + pressure drag
= 23.37+0.3457 = 23.71 N
Fig. Drag coefficient of laminar and turbulent boundary layers
on smooth and rough flat plates
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7.3. ADDED MASS:
It is a phenomenon which affects the underwater vehicles. When a body moves
underwater, the immediate surrounding fluid is accelerated along with the body. This
affects the dynamics of the vehicle in such a way that the force required to accelerate
the water can be modelled as an added mass. Added mass is a fairly significant effect
and is related to the mass and inertial values of the vehicle.
Added mass is comparatively a smaller value and is dependent only upon the normal
surface area and that to only for the time till which the body accelerating.
8. VEHICLE SPEED
The design speed we have decided for our AUV is 1m/s.
8.1. THE DRAG VARIATION WITH VELOCITY IS GIVEN BY THE GRAPH BELOW
Drag = Cd x density x V2 x area/2
Drag is directly proportional to the (velocity)2
.
0
20
40
60
80
100
120
140
160
0 0.5 1 1.5 2 2.5 3
DRAG Vs VELOCITY
Velocity(m/s)
Drag
(N)
____Pressure drag
____Skin drag
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9. POWER BUDGET AND TYPE OF BATTERY
As in any marine vehicle design the buoyancy and the weight needs to be carefully
balanced. This is even more crucial for submerged vehicles that must operate at a
state of neutral buoyancy. Increasing weight leads to increasing volume which in turn
will lead to increasing power requirement and thus in turn in weight. This cycle needs
to be balanced and often involves several stages.
After the thrust and drag calculations are done above as shown we then move on for
power calculations.
The total drag based on which the design is to be performed is thus (1+k) RT where
k is service allowance including appendage drag. Typical value of k taken in ship
design lies between 15-20%. The thrust required by the thruster is determined from
the relation (1-t)T=(1+k)RT where T is the thrust and t is the thrust deduction factor.
Alternatively the required thrust power can be calculated from the following relation,
PDB=Peff/nD; Peff = (1+k) RTV
Where PDB is the power to be delivered at the thruster, Peff is the effective power ,
and nD is the so-called quasi propulsive coefficient for a marine propeller , given by
the relation nD=nHnRno
Where,
nH : The ratio of work done on the body to that done by the thruster =(1-t)/(1-w)
nR : The ratio of behind to open water efficiencies
no : Propeller open water efficiency
w in the above is the wake fraction.
From the various data available for marine screw propellers nH can be taken around
1 and nR can be taken around 0.9. It is the open water efficiency that has the largest
influence on the total efficiency. For the size of thruster typical to AUV’s (small
propellers at high RPM with relatively low blade area ratios), this value is somewhat
lower than conventional marine propellers. Considering all factors, a value of 0.5 for
no appears to be a reasonable estimate.
The above is applicable for forward motions. While performing manoeuvers the
vehicle must also perform sway and yaw. If these manoeuvring motions are to be
induced by thrusters the power requirements must also be estimated. The moment
needed for yaw is much smaller than sway and is thus ignored as far as the vehicles
total power requirement is concerned. For sway the main drag will be due to viscous
pressure drag, or cross flow drag ; the skin friction drag is much smaller and is hence
ignored for all practical purposes
For our AUV we have found the net forward drag = (1+k)*drag calculated=
(1+1.5)*23.71= 59.275 N.
Hence net power requirement is given by Force * Velocity= 59.275*1 =59.275 W.
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9.1. PAYLOAD POWER BUDGET:
Camera 2 W
CTD Sensor 5 W
Motherboard + Microprocessor 15 W
Torch 15 W
URF 0.2 W
Heading Sensor 0.4 W
DVL 10 W
TOTAL 47.6 W
Total Power = drag power + payload power = 59.275+47.6= 106.875 W
9.2. ENDURANCE
The endurance of our AUV is minimum 2hour 15 minutes and it can travel minimum of
16.2 km.
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9.3. TYPE OF BATTERY:
The following statistics are the criterion on which battery selection has been done.
The main aim is to choose a high capacity and high durable battery which according
to the battery is a Li ion battery.
Fig. Comparisons of power from various types of battery
The power rating is chosen according to the then calculated power of the systems.
The AUV is being powered by 4 Lithium ion battery (11.1V, 3Ah) and 1 Lithium
Ion Battery (24V, 9Ah). 4 Lithium Ion battery powers the thrusters. The other
battery is connected to the power converters which powers the motherboard. This
battery also powers sensors after passing through a DCDC converter.
Both of the batteries have monitoring system which does coulomb counting and
makes the system to shut down when it runs low
Dimension: 24 x 47 x 109 (mm)
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10. NAVIGATION AND CONTROL
The objective of this sub system is to enable the AUV to track through a predefined
trajectory starting from launch to retrieval. The onboard computers provide guidance,
control, and system management using both sensors and actuators. The desired
activities to be carried out during its mission can be broadly classified as vehicle motion
management and control navigation, onboard intelligence for autonomy and
management of the entire onboard housekeeping.
Data Diagram of the Navigation System:
11. SENSORS AND EQUIPMENTS
The electrical system of the JALNETRA sought to fulfil the following:
Provide for motion control
Water leakage detection
32. 32 | P a g e
Energy control and recharge possibility
Communication and sonar-vision processing
Easy and reliable design
All controller values soft coded for easy modifications
Deal with electromagnetic noise and sensitive noises
Measure the vehicle’s depth
Measure the vehicle’s surge velocity
11.1. SENSORS:
11.1.1. CTD3100 (CONDUCTIVITY, TEMPERATURE, DEPTH) SENSOR:
We are using a CTD which provides a complete self-contained measurement and data
logging system for a wide range of environmental water monitoring applications.
Manufacturer: Greenspan Analytical Pty Ltd.
Depth rating-100m
Weight - 950gm
Operating temperature: 0-50° C
Power supply: 8 to 30 V dc
Lead time: 45 days
Features:
Conductivity measurements via toroidal Sensor
Storage of raw EC, temp and normalized EC to25 degrees
Low power usage enables long term remote operation
Internal data logger for collection of data during critical events
Telemetry options via mobile phone, radio and satellite
SDI12 cable adaptor unit for connection into data logger or controls
33. 33 | P a g e
Benefits:
Can be installed in active waters (acidic or salty conditions)
Reliable and robust sensor ensures minimal field visits for maintenance
Suitable for marine applications and waterways with high sediment loads
Easy to configure logger – quick retrieval of data
Graphical and tabular display – export to spreadsheet format.
Flowchart of CTD Sensor and it’s working:
11.1.2. DOPPLER VELOCITY LOG:
A mini Laser Doppler Velocity meter (DVL) system is used to measure the forward
longitudinal velocity of the vehicle. It consists of a Transceiver probe, Processing Engine
and Burst Processor software. We are using this because it is very small and gives
accurate measurement of 0.997. And has a great range of 1mm/sec to 300m/sec.
Manufacturer: Measurement Science Enterprise, Inc.
Dimensions: 32mm (dia) x 165mm (long)
Weight: 250gm
Operating temperature: 0-65° C, 35 bar (max)
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Fig. DVL
Power supply: 12V
Lead time: 15 days
Flowchart diagram of the mini LDV and its working:
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11.1.3. HEADING SENSOR:
After a lot of research we got a small robust MTi (miniature attitude and heading
reference) which gave a remarkable accuracy in
terms of orientation, dynamic data and immunity to
magnetic disturbances. Our on-board digital
processor outputs orientation for instantaneous
control. It is used as stable compass also. Its
direct low-level communication allows full and
easy control. It also helps in orientation correction
for TLT-2 system. It can sense 3 DOF of
orientation, acceleration, rate of turn, magnetic
field.
Manufacturer: XSENS Technologies
Dimensions: 58x58x22 mm
Weight: 50gm
Operating voltage 4, 5-30 V
Operating temperature: -40° to +85° C
Flowchart diagram of heading sensor and its working:
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11.1.4. SRF004 ULTRASONIC RANGE SENSOR:
This sensor detects objects in its path and can be used to calculate the range of the
object. The reason of using is that it is sensitive enough to detect a 3cm diameter broom
handle at a distance of over 2m.
Manufacturer: Revolution Education Ltd.
Dimensions: 43x20x17 mm
Its work explained with an algorithm
Symbol trig=3 ‘Define output pin for Trigger pulse ‘
Symbol echo=6 ‘Define input pin for Echo pulse ‘
Symbol range=w1 ‘16 bit word variable for range ‘
Main:
Let pins = %10100000 ‘auv forward’
Loop:
Pulse out trig, 2 ‘produce 20us trigger pulse’
‘(Must be minimum of 10us)
Pulse in echo, 1, range ‘measures the range in 10us steps ‘
Pause 10 ‘SRF004 mandatory 10mS recharge period’
‘After ranging completes
‘Now convert range to cm (di vide by 6.2) or inches (divide by 14.9)
‘And stop if there is an object closer than 30cm
Let range = range*10/62 ‘multiply by 10 then divide by 62 ‘
If range < 30 then stop
Go to loop ‘loop around if >30
Stop
Voltage: 5V
Current: 30mA-50mA
Frequency: 40 KHz
Range: 0.03-3 m
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11.2 THRUSTERS:
There are four thrusters primarily in use in AUV JAL NETRA 3.O. There are two
forward facing thrusters for the forward and backward motion. These two are placed
at the sides of the AUV parallel to each other. They also eliminate the need for a
secondary turning device as voltage modulation in either one of them will produce
the desired rate of turn as and when required. The other two thrusters are placed at
the fore and aft end of the AUV. The AUV as designed is a positively buoyant
vehicle, and hence the two vertical thrusters will be used to submerge the AUV, once
again the desired depth can be obtained by the corresponding voltage variation. We
have used SEABOTIX thrusters for the purpose as shown in the figure.
Dimensions: ϕ 9.5 cm x 17.5 cm
Specifications:
Depth rating: 150 meters
Voltage: +19.1 V DC
Power: 110W Max (depending upon RPM or Drag)
Max amperage: 5.8 amps
Max continuous amperage: 4.25 amps
Weight: 705 gms (in air), 350 gms (in fresh water)
Peak bollard thrust: 2.9 KGF
Continual bollard thrust: 2.2 KGF
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11.2.1. PROCESSING UNITS:
In order to retain the modular design of the system and also isolate each high
processing requirement electronic system as best possible from the other, Jal Netra
makes use of multiple processing units that are organized in a Master-Slave relationship.
Each of these processing systems was chosen since they are best suited to the task that
they perform. Currently, the AUV utilizes a VIA EPIA Mini- ITX form factor M10000 x86
systems as the master controller along with two slave microcontrollers, the Atmel avr
at32uc3a0512 and Savage Innovations microPIC 16-bit PIC24 MCUs and dsPIC®
DSCs.
11.2.2. VIA EPIA Mini- ITX M10000:
The VIA EPIA Mini-ITX M10000 is a compact x86 processor architecture based single
board computer system equipped with the low power consumption and small footprint
VIA Nehemiah C3 1GHz processor. The M10000 in Jal Netra provides 2 on board IDE
connectors, a 10/100 Base-T Ethernet port and two PS2, one RS-232 and two USB 2.0
I/O ports, all of which fit into a small form factor of 17cm x 17cm along with 256 MB
DDR266 RAM. In order to expand the number of USB and RS-232 ports available a four
port USB hub along with USB to RS-232 COM port converters are used. Utilizing this
platform as the master processing unit allows us to rapidly program software in a familiar
development environment and utilize the benefits of easily available components for the
system. The CPU and RAM provide enough processing capabilities for all the tasks the
M10000 is assigned.
All sensors and other peripheral devices interface with this main PC board through the
slave processing units over the RS-232 protocol. The only systems to directly interface
with the M10000 over a USB
Connection is the two webcams used for image processing tasks. All data gathered from
these devices is logged to a 60 GB IDE hard drive.
The Ethernet link of 100 Mbps to the vehicle is used to control, develop and test the
vehicle before it is placed into competition mode. Data can be collected in real-time over
this link; it also allows the vehicle to be remotely operated like a ROV and for in place
programming and debugging utilizing tools already placed on the AUV.
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11.2.3. ATMEL AVR AT32UC3A0512:
It is a 32-bit flash microcontroller based on 32-bit AVR UC core featuring 512kb flash,
64kb sram, 10/100 ethernet mac, full-speed (12 mbps) usb 2.0 with on-the-go (otg)
capability, i2s, built-in audio dac. The at32uc3a0512 also feature sram/ sdram external
bus interface (ebi). The AT32UC3A devices deliver 91 Dhrystone mips (dmips) at 66
mhz and consume only 40 mA at 3.3v.
It is used as a sensor interface in our AUV.
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11.2.4.SAVAGE INNOVATIONS microPIC:
Model used is 16-bit PIC24 MCUs and dsPIC® DSCs. It is a robust design used as
navigation interface in AUV JALNETRA
Broad Portfolio
* Pin and code compatible across families
* 16 to 40 MIPS PIC24 MCU & dsPIC® DSC families
Fig. 35 savage innovations micropic
* Flexible memory options up to 256 KB
Innovative Peripherals
* Graphics Control and Interface
* PMP for Graphics Display Interface
* USB-OTG, CAN, LIN and More
* Digital Power Conversion and Motor Control
Real-Time Control
* Single cycle execution
* Integrated WDT, POR, BOR and LVD
* Fast DMA
Free Software Libraries
* Graphics, mTouch™ Sensing Solutions and Speech
* USB-OTG, CAN and Ethernet
* Motor Control, SMPS and Audio
C families
* Flexible memory options up to 256 KB
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11.2.5. PROPRIOCEPTIVE SENSOR:
One of the conditions for triggering the buoyancy control device to empty the buoyancy
tanks is the presence of water being sensed by the AUV. The sensor used for this
application is called a Proprioceptive sensor. This sensor gives out a signal as soon as it
detects presence of water or any fluid in the vicinity. As the fore end of an AUV is the
most susceptible to impact related damages, this sensor is placed in the fore half of the
AUV. The Proprioceptive sensor which we used is Zircon Leak Alert Water Detector;
model no: Q506-6403.
The actual functioning of this sensor is such that the device gives a sound alarm when it
detects water but we have reformatted it such that it will give a trigger impulse to the
buoyancy control device to empty the buoyancy tanks and the AUV resurfaces.
POWER: Two AA Batteries
12. ENDURANCE AND RANGE OF AUV COVERAGE
12.1. ENDURANCE:
Fig. 36
The endurance of an auv depends on the above factors and the endurance is said to be
high if the balance is set between the criterions. For evaluating the above we refer to the
below details i.e. volume per surface area, power v/s speed. These will give the heat
dissipation rate and the efficient speed at which minimum power consumption is
observed.
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12.2. RANGE OF MISSIONS THAT THE AUV CAN UNDERTAKE:
a) Station Keeping: In many cases at docks and busy ports huge vessels have to be
monitored while in motion while entering or leaving the port. Here the AUV can one of
the major players in guiding the ships. The underwater terrain of a port is the primary
concern of any major ocean going body entering the as it cannot be sensed by the
transponder here the AUV can assist in manoeuvring the ship.
b) Coral reefs survey is one of the major areas of application of AUV. As we all know the
pollution caused at the seas leads to the discolouration and ultimately destruction. The
surveillance of the coral reefs and the apparent effects caused on them due to pollution
and other natural phenomenon like upwelling and down welling along with the effects of
thermo cline can be observed with the high definition camera on board AUV Jal Netra
c) One of the most important processes in the coastal ocean is upwelling, the movement
of water from deeper layers of the sea to the surface. It constitutes the other major
process for nutrient regeneration in the surface layer; in terms of magnitude and
importance it has to be ranked before the process of nutrient regeneration through tidal
mixing.
d) Upwelling in the coastal ocean can be due to a
number of factors. In most situations the upwelling
is wind driven and its effect on currents,
stratification and nutrient supply determined by
topographic detail such as water depth and the
shape of the coastline. In other situations it is the
response to variations in the currents found just
outside the coastal ocean and therefore
independent of coastal wind conditions.
e) Down welling is the process
of accumulation and sinking of
higher density material beneath
lower density material, such as
cold or saline water beneath
warmer or fresher water or cold
air beneath warm air. It is the
sinking limb of a
convection cell. Upwelling is the
opposite process and together
these two forces are responsible
in the oceans for the thermo
cline circulation. The sinking of
cold lithosphere at subduction
zones is another example of
down welling in plate tectonics. Down welling occurs at anti-cyclonic places within the
ocean where warm rings are spinning clockwise creating surface convergence.
Fig. Upwelling
Fig. downwelling
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f) Thermo clines play a key role in ocean circulation, marine ecology, and underwater
acoustics. In oceanographic surveys, it is often desirable to detect the thermo cline and
track its spatiotemporal variation. Mobility of an autonomous underwater vehicle (AUV)
makes it an efficient platform for thermo cline tracking. In this paper, we present a fully
autonomous algorithm for detecting and tracking the thermo cline by an AUV. The key is
detection of the peak gradient of temperature. We have tested the algorithm by post-
processing data from a previous Dorado AUV survey over the northern Monterey Bay
shelf.
Fig. thermoclines
The above phenomenon is one of the influencing factors in the coral reef research. Apart
from this it will also do the function of filming the ocean floor, detecting the floor activity,
depth, and pressure variation scanning; these activities are really helpful in case of study
of coral reefs which are endangered.
g) The primary reason for which the concept of AUV was developed in the first place
was the oceanographic surveys of various underwater phenomenon along with the
observation of aquatic flora and fauna.
h) With appropriate change of instrumentation AUV Jal Netra is capable of collecting
samples of water at particular location and brings it up for further analysis.
i) Another main area of application of AUVs is the survey and maintenance of
underwater pipelines and cables.
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Fig. Some Typical Missions of AUV
13. TYPE OF CONTROLLER AND CONTROL ALGORITHMS
The controller we are using in our AUV system is a PID (progressive integrated
derivative)
The transfer function of the PID controller looks like the following:
o Kp = Proportional gain
o KI = Integral gain
o Kd = Derivative gain
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First, let's take a look at how the PID controller works in a closed-loop system using the
schematic shown above. The variable (e) represents the tracking error, the difference
between the desired input value (R) and the actual output (Y). This error signal (e) will
be sent to the PID controller, and the controller computes both the derivative and the
integral of this error signal. The signal (u) just past the controller is now equal to the
proportional gain (Kp) times the magnitude of the error plus the integral gain (Ki) times
the integral of the error plus the derivative gain (Kd) times the derivative of the error.
47. 47 | P a g e
This signal (u) will be sent to the plant, and the new output (Y) will be obtained. This new
output (Y) will be sent back to the sensor again to find the new error signal (e). The
controller takes this new error signal and computes its derivative and its integral again.
This process goes on and on.
13.1. THE CHARACTERISTICS OF P, I, AND D CONTROLLERS
A proportional controller (Kp) will have the effect of reducing the rise time and will reduce
,but never eliminate, the steady-state error. An integral control (Ki) will have the effect of
eliminating the steady-state error, but it may make the transient response worse. A
derivative control (Kd) will have the effect of increasing the stability of the system,
reducing the overshoot, and improving the transient response. Effects of each of
controllers Kp, Kd, and Ki on a closed-loop system are summarized in the table shown
below.
13.2. PROPORTIONAL CONTROL
From the table shown above, we see that the proportional controller (Kp) reduces the
rise time, increases the overshoot, and reduces the steady-state error. The closed-loop
transfer function of the above system with a proportional controller is:
13.3. PROPORTIONAL-INTEGRAL CONTROL
From the table, we see that an integral controller (Ki) decreases the rise time, increases
both the overshoot and the settling time, and eliminates the steady-state error. For the
given system, the closed-loop transfer function with a PI control is:
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13.4. PROPORTIONAL-INTEGRAL-DERIVATIVE CONTROL
Now, let's take a look at a PID controller. The closed-loop transfer function of the given
system with a PID controller is:
14. MANOEUVERABILITY (THRUSTER POSITION DESIGN)
Manoeuvrability is a very important aspect of AUV navigation and design. The primary
underwater motion we are trying to target in AUV Jal Netra are:
1. Surge (X axis): The two thrusters alongside the frame take care of this motion. The
propulsion provided by this motion is utilized for surge.
2. Sway (Y axis): This is not a motion commonly found in underwater bodies as it caused
huge drag in the direction as the normal area is huge in long and slender bodies. As far
as the designed motions go sway is not considered in AUV Jal Netra.
3. Heave (Z axis): The heave motion is not an issue as far as AUV Jal Netra is
concerned as the body is neutrally buoyant, the up and down motion within the water
can be modulated by the two thrusters placed at bow and stern.
4. Roll (X axis): The design of the vehicle is such that the CG and CB are virtually in a
single straight line and the difference between them is 4.6 cm to bring the AUV back at
any angle of inclination the max GZ available is 116.9595Kg-m.
5. Pitch (Y Axis): This motion is not considered in AUV Jalnetra.
6. Yaw (Z axis): This is one of the primary designed motions of the AUV. There are three
systems designed to control this motion. Let’s say the AUV needs to turn in one
particular direction then the motion is controlled by regulating the two thrusters backed
up by a strong line following algorithm.
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15. OBSTACLE AVOIDANCE
Obstacle avoidance in AUV Jal Netra is basically done by the range sensor. It is so
programmed as to detect small curves and objects of the orders 3inches in diameter
over a distance of 2 m and away. This data is therefore fed in to a smart PATHFINDER
which on its own will decide upon the alternative path.
Further work will also be done in this case to develop software for obstacle avoidance.
Fig. Flowchart of obstacle avoidance
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16. CAMERA BASED IMAGING WITH LIGHTS
16.1. CAMERA SPECIFICATIONS:
The camera we are using in our AUV is LOGITECH WEBCAM PRO 9000 which records
720p HD videos of the underwater scenario and is 2MP.
Manufacturer: Logitech Pvt. Ltd.
Model No. : WEBCAM PRO 9000
Power: 2 watts
Lead time: 5 days
16.2. XENON FLASHER :
We are using 2 xenon flashers of 5 watts. This
will give ambient light for camera to take
videos.
*These webcams interface directly with the x86
based M10000 over high speed USB ports.
Further work will be done on this subject for the
integrating the cameras into the obstacle
avoidance and helping in motion of the control.
16.3 PNEUMATICS SYSTEM:
A pneumatic system is proposed to have in JAL NETRA 3.0 replacing gravity and
motion arrangement in previous versions for the purpose of marker dropper and
torpedo launcher. The system uses compressed air which is stored inside a paintball
pressure tank. This pressure is regulated to 8 bars by using a pressure regulator.
The output of regulator is connected to a 2/2 solenoid valve which act as switch and
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cuts the gas supply in case of any failure. The output of the solenoid valve is
connected to a distributor which distributes gas to four 2/2 solenoid valves. Outputs
of 2/2 solenoid valves are connected to two pneumatic cylinders of marker dropper
and two of torpedo launcher.
17. LAUNCH AND RECOVERY
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The safe launch and recovery of an AUV are small but extremely important phases
of a mission. AUV Jal Netra being pretty light in weight can be launched manually or
can be triggered within the water by a RF signal.
The recovery of the AUV can similarly have following method-
Once the stipulated mission is completed the AUV is pre-fed with coordinates at
which it has to dock. After the mission the AUV comes to those coordinates and the
thrusters is triggered to switch off and the AUV comes floating up to the surface
since it is neutrally buoyant.
The trigger to the AUV‟s propulsion system and launch may be provided by
Bluetooth signal or RF signal depending on the device available
FAIL-SAFE mechanism is triggered in these cases also:
1. The batteries untimely run out of charge or microprocessor crashes
2. Any exterior damage to the hull causing flooding or deformation of the pressure
hull
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18. SOFTWARE CONTROL
Software development for the AUV has been done in VB .NET, MATLAB, C and Perl
running on Windows XP Professional. The memory resident component of the control
software places the AUV into development mode automatically when an Ethernet
connection is detected; this makes all the development tools for the aforementioned
languages accessible to the programmers. This same connection can also be utilized to
observe sensor values and reprogram the μCs connected to the M10000.
CONCLUSION:
From the above study and data collection for AUV JALNETRA we have come up with a
practical, economic and versatile AUV model.
REFERENCES:
[1] O. Xu. Autonomous underwater vehicles (auvs). Report, The University of Western
Australia, 2004.
[2] J. Yuh. Design and control of autonomous underwater robots: A survey. [online],
2000. Available: http://neuron-ai.tuke.sk/_hudecm/PDF
PAPERS/DesignAndControlOfAutonomousUnderwaterrobotsASurvey.pdf/.
54. 54 | P a g e
[3] Autonomous underwater vehicles. [online], 2003. Available: http://www.geo-
prose.com/ALPS/white papers/alt.pdf/.
[4] Blue fin robotics. [Online], 2004. Available: http://www.bluefin.com/auv.htm/.
[5] Nps center for auv research. [online], 2003. Available:
http://www.cs.nps.navy.mil/research/auv/.
[6] Nekton research ltd. [online], 2003. Available: http://www.nektonresearch.com/.
[7] Technical Paper Presented by J.G. Bellingham et al. 2010 Ocean Sciences Meeting.
[8] PNA Volume
