modelling, simulation and control of underwater vehicles
DESCRIPTION
Hội nghị toàn quốc về Điều khiển và Tự động hoá - VCCA-2011Modelling, Simulation and Control of Underwater Vehicles Mô hình hóa, mô phỏng và điều khiển phương tiện ngầmHung Duc Nguyen, Riaan Pienaar, Dev Ranmuthugala and William West University of Tasmania / Australian Maritime College e-Mail: [email protected] AbstractUnderwater vehicles have been developed over many decades for exploration of seabed, discovery and exploitation of marine resources. Maintaining control of underwater vehiclTRANSCRIPT
Hội nghị toàn quốc về Điều khiển và Tự động hoá - VCCA-2011
VCCA-2011
Modelling, Simulation and Control of Underwater Vehicles
Mô hình hóa, mô phỏng và điều khiển phương tiện ngầm
Hung Duc Nguyen, Riaan Pienaar, Dev Ranmuthugala and William West
University of Tasmania / Australian Maritime College
e-Mail: [email protected]
Abstract Underwater vehicles have been developed over many
decades for exploration of seabed, discovery and
exploitation of marine resources. Maintaining control
of underwater vehicles for various missions at seas
requires a good understanding of the underwater
vehicle hydrodynamics and control characteristics. In
order to get students involved in the development of
control systems for underwater vehicles it is necessary
to have a working underwater vehicle with a fully-
functioned controller to do design and implement
missions. This paper presents the modelling,
simulation and control of a newly-built underwater
vehicle for academic and research purposes. A series
of small underwater vehicles have been designed and
built at the Australian Maritime College (University
of Tasmania) within the maritime engineering course
final year programmes. This includes the development
of mathematical models of these small underwater
vehicles for simulation and control design purposes.
This paper focuses on theoretical modelling,
simulation, control design and testings of the AMC
newly-built ROV/AUV.
Tóm tắt: Phương tiện ngầm đã được phát triển qua
nhiều thập niên dùng cho nhiều mục đích khác nhau
như thám hiểm đáy đại dương, thăm dò và khai thác
tài nguyên biển. Điều khiển duy trì phương tiện ngầm
làm các nhiệm vụ khác nhau trên biển đòi hỏi cần
phải hiểu rõ thủy động lực học và đặc tính điều khiển
của phương tiện ngầm. Nhằm để cho sinh viên phát
triển hệ thống điều khiển cho phương tiện ngầm cần
phải có một mô hình phương tiện ngầm hoạt động
được với một bộ điều khiển đầy đủ chức năng để thiết
kế và thực hiện nhiệm vụ. Bài báo này trình bày mô
hình hóa, mô phỏng và điều khiển một phương tiện
ngầm mới đóng để dùng cho mục đích giảng dạy và
nghiên cứu. Tại AMC (Đại học Tasmania) sinh viên
thiết kế và đóng một số phương tiện ngầm loại nhỏ
trong các chương trình cuối năm của khóa học công
nghệ hàng hải. Bài báo này bao gồm cả việc phát triển
mô hình toán của các phương tiện ngầm lọai nhỏ này
dùng cho mục đích mô phỏng và thiết kế điều khiển.
Bài báo này tập trung vào mô hình hóa lý thuyết, mô
phỏng, thiết kế điều khiển và tthử nghiệm phương tiện
ngầm mới đóng của AMC.
Nomenclature
Symbol Unit Meaning ν
Tu,v,w,p,q, rν
η T
n,e,d, , , η
Abbreviation DOF Degree of freedom
ROV Remotely operated vehicle
AUV Autonomous underwater vehicle
HIL Hardware in the loop
AMC Australian Maritime College
UTAS University of Tasmania
HAIN Hydroacoustic aided inertial navigation
1. Introduction Underwater vehicles require mathematical models to
describe behaviour and dynamics. Modelling
underwater vehicles usually has two aspects: one is
theoretical modelling and the other physical testing.
Around the world there are many institutes
developing underwater vehicles for various purposes.
AMC has developed a series of ROVs/AUVs for
academic uses. The goal is to build a virtual lab (a
HIL simulation program) of ROVs/AUVs that
interacts CFD software with a simulation program. A
virtual ROV/AUV will be controlled by a joystick
managed through an appropriate simulation program.
Possible applications of ROVs/AUVs are:
observe seabed conditions;
observe marine farms;
conduct underwater seismic survey for
discovery of oil and gas and exploitation of
marine resources; and
surveillance operation.
As the first step to realize such a virtual lab for
ROVs/AUVs, it is necessary to develop mathematical
models for vehicles. The main purpose of this paper is
to:
describe the AMC ROV/AUV;
model the ROV/AUV using relevant theory;
simulate the ROV/AUV;
design a controller for the ROV/AUV
preliminarily; and
design captive test for the estimation of the
hydrodynamic coefficients and validation of
the assumed model.
The paper is organized as follows: Section 1
introduction, Section 2 reference frames and
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equations of kinematics and kinetics, Section 3 brief
description of the AMC ROV/AUV, Section 4 control
algorithms and design of experiments, Section 5
model scaled experiments and Section 6 conclusions.
Additional information is given in Appendix.
2. Reference Frames and Equations Two reference frames for underwater vehicles are
shown in Fig. 1. NED is the earth-fixed reference
frame and XYZ is the body-fixed reference frame.
Fig. 1 Reference frames for underwater vehicles
2.1 Kinematics
Referring to Fig. 1 the 6-DOF kinematic equations in
the NED (north-east-down) reference frame in the
vector form are [3][4],
η J η ν (1)
where
n
b 3 3
3 3
R Θ 0J η
0 T Θ (2)
with 3 3S η and 3ν . The angle rotation
matrix n 3 3
b
R Θ is defined in terms of the
principal rotations,
x,
1 0 0
0 c s
0 s c
R , y,
c 0 s
0 1 0
s 0 c
R and
z,
c s 0
s c 0
0 0 1
R (3)
where s =sin(.), c = cos(.) using the zyx-convention,
n
b z, y, x,: R Θ R R R (4)
or
n
b
c c s c c s s s s c c s
s c c c s s s c s s s c
s c s c c
R Θ
(5)
The inverse transformation satisfies,
1n b T T T
b n x, y, z,
R Θ R Θ R R R (6)
The Euler angle attitude transformation matrix is:
1 s t c t
0 c s
0 s / c c / c
T Θ
1
1 0 s
0 c c s
0 s c c
T Θ o90 (7)
It should be noted that T Θ is undefined for a
pitch angle of o90 and that 1 T
T Θ T Θ .
2.2 Kinetics
The 6-DOF kinetic equations in the body-fixed
reference frame in the vector form [3] are therefore,
0 wind wave Mν C ν ν D ν ν g η g τ τ τ (8)
where
M = MRB+MA: system inertia matrix (including added
mass)
C ν = RB AC ν C ν : Coriolis-centripetal matrix
(including added mass)
D ν : damping matrix
g η : vector of gravitational/buoyancy forces and
moments
0g : vector used for pretrimming (ballast control)
τ : vector of control inputs
windτ : vector of wind-induced forces and moments
waveτ : vector of wave-induced forces and moments
2.3 Mathematical Model with Environmental
Disturbances
In order to improve performance of the control
systems for underwater vehicles it is necessary to
consider effects of external disturbances on
underwater vehicles, which include wind, waves and
currents. According to Fossen [3], for control system
design it is common to assume the principle of
superposition when considering wind and wave
disturbances. In general, the environmental forces and
moments will be highly nonlinear and both additive
and multiplicative to the dynamic equations of
motion. An accurate description of the environmental
forces and moments is important in vessel simulators
that are produced for human operators.
With effects of external disturbances Equation (8) is
rewritten as [3][4],
RB RB A r A r r r r
0
M ν C ν ν M ν C ν ν D ν ν
g η g τ w (9)
where wind wave w τ τ and
r c ν ν ν (where
6
c ν is the velocity of the ocean current expressed
in the NED). Further information on modelling
environmental disturbances can be found in [2][3].
3. Brief Description of AMC’s
ROV/AUV-3 3.1 Dimensions of AMC ROV/AUV-3
The 3rd
generation of AMC ROV/AUV is named
AMC ROV/AUV-3. The main particulars of the
vehicle are given in Table 1. Fig.2 shows the AMC
ROV/AUV-3 which has been tested for watertight
N
E D
O
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integrity to a depth of 40 metres. Fig. 3 and Fig. 4
show the arrangement of its sensors and actuators.
Two boxes named Box 1 and Box 2 are provided for
electronics and batteries.
Table 1 Main particulars of AMC ROV/AUV-3
Length over all 830 mm
Width of frame 285 mm
Overall width 445 mm
Height 265 mm
Height with light 323 mm
Weight in the air 17.1 kg
Fig. 2 The 3rd generation of AMC ROV/AUV-3
Fig. 3 Body-fixed reference frame of AMC ROV/AUV-3
Fig. 4 Arrangement of thrsuters of AMC ROV/AUV-3 (ui, i
= 1 to 3, are the voltage inputs of thrusters)
AMC ROV/AUV-3 is equipped with the following
sensors and actuators (see Fig. 5):
sensors: 6-DOF IMU, pressure/depth sensor
actuators/thrusters: 3 Seabotix thrusters
(Model BTD150);
servo motor to control the forward camera; and
three lights.
3.2 4-DOF Mathematical Model (block-shaped
ROV)
In order to derive the differential equations governing
the dynamics of the vehicle, it is assumed that:
the origin of the body-fixed reference frame is
at the centre of gravity where the vertical
thruster is located;
the body has an equivalent block shape; and
the rolling and pitch motion can be neglected.
Fig. 5 Input and output variables of the AMC ROV/AUV-3
Thus, the 6-DOF model in Equation (9) is simplified
to a 4-DOF model as follows [2][3][4].
Kinematics:
η J η ν (10)
Kinetics:
Mν C ν D ν g Bu (11)
where:
x
y
z
η ;
c s 0 0
s c 0 0
0 0 1 0
0 0 0 1
J ;
u
v
w
r
ν ;
u
v
w
z r
m X 0 0 0
0 m Y 0 0
0 0 m Z 0
0 0 0 I N
M ;
v
u
v u
0 mr 0 Y v
mr 0 0 X u
0 0 0 0
Y v X u 0 0
C ν ;
u u
v v
w w
r r
X u 0 0 0
0 Y v 0 0
0 0 Z w 0
0 0 0 N r
D ν ;
0
0
0
0
g ;
k 0 k
0 0 0
0 0 k
kl 0 kl
B ; and
1
2
3
u
u
u
u
Numerical values of the coefficients in Equations (10)
and (11) are given in Table 2 in Appendix.
4. Control Algorithms and Design of
Experiments In order to design a controller for missions at sea, the
automatic control system as a whole is illustrated in
Fig. 6 showing the signal flow of guidance,
navigation and control systems.
G
u2
u1
u3
Thruster 1
Thruster 2
Thruster 3 Box 1 Box 2
Torch 1
Camera
house
Torch 2
Pressure
sensor
Y
Z
X
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Guidance system: to receive prior information,
predefined inputs and waypoints and generate
desired trajectory including desired speed,
depth (heave), yaw and position. A joystick
may be used to generate reference signals
[3][4][7].
Navigation system: equipped with GNSS/INS
receivers and other sensors to provide
measurement of speed, depth, yaw and
position [3][4][7]; and
Control system: to detect error by comparing
speed, depth, heading angle and position with
desired values and calculate control signals
and send them to the controller allocation
devices (actuators) [3][4][7].
Fig. 6 Guidance, Navigation and Control signal flow [3]
Fig. 7 shows an arrangement of sensors, actuators and
target PC (onboard equipment) and their connection
to a host PC with software.
Fig. 7 Arrangement of sensors, actuators and connection of
the target PC to the host PC
In general controls of a ROV/AUV include:
heading control:
speed, depth (heave) and pitch control;
roll, surge and sway; and
position control.
As the first step to realize a hardware-in-the-loop
system, computer simulation programs are developed
using the mathematical model in Equations (10) and
(11). A number of tests are carried out for the
simulation programmes including:
open-loop system tests;
manoeuvring tests; and
closed-loop system tests.
In the simulation programs for closed-loop control
systems (including depth and course keeping, pitch
and roll control and position control) the conventional
PID control law was used:
P I D
d tu K e t K e t dt K
dt (28)
4.1 Open-Loop System: Straight ahead and
Turning Circle Manoeuvres
With different values of voltage inputs of two
thrusters at a certain depth, the following were tested
with the simulation programmes:
u = [12 12 0] straight ahead (Fig. 8)
u = [12 -12 0] left turn (Fig. 9)
u = [-12 12 0] right turn (Fig. 10).
-80-60
-40-20
020
-1
-0.5
0
0.5
1-101
-100.5
-100
-99.5
-99
z p
os.
x pos.y pos.
Fig. 8 Straight ahead (z(0) = 100 m)
-2
0
2
4
6
-5
0
5
10-101
-100.5
-100
-99.5
-99
z p
os.
x pos.y pos.
Fig. 9 Left turn (z(0) = 100 m)
-2
0
2
4
6
-10
-5
0
5-101
-100.5
-100
-99.5
-99
z p
os.
x pos.y pos.
Fig. 10 Right turn (z(0) = 100 m)
Estimated
position and
velocities
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4.2 Open-loop System: Depth Control Manoeuvres
Depth control (including driving and surfacing) of the
AMC ROV/AUV-3 was done by the computer
simulation as follows:
u = [12 12 12]: diving (Fig. 11)
u = [12 12 -12]: surfacing (Fig. 12).
-80-60
-40-20
020
-1
-0.5
0
0.5
1-160
-150
-140
-130
-120
-110
-100
x pos.y pos.
z p
os.
Fig. 11 Diving (z(0) = 100 m)
-80-60
-40-20
020
-1
-0.5
0
0.5
1-100
-90
-80
-70
-60
-50
-40
x pos.y pos.
z p
os.
Fig. 12 Surfacing (z(0) = 100 m)
4.3 Depth and Yaw Control (Zigzag Manoeuvres,
Course/Depth Keeping and Changing)
In order to design automatic multitask mission
manoeuvring systems for the ROV/AUV, zigzag tests
(depth), depth control and course keeping and
changing control were carried out as shown below.
Zigzag tests (depth) (Fig. 13);
-50
0
50
100
150
-1
-0.5
0
0.5
1-115
-110
-105
-100
-95
-90
-85
x pos.y pos.
z p
os.
Fig. 13 Zigzag test (u3 = 10 V, change in z = 10 m)
Depth control with PID controller (Fig. 14);
0 50 100 150 200 250 300-115
-110
-105
-100
-95
-90
-85Depth Control - 2D Plotting
Time [s]
Heave [
m]
(a) 2-D plotting
-150
-100
-50
0
50
-1
0
1
2
x 10-14
-115
-110
-105
-100
-95
-90
-85
x pos.
Depth Control - 3D Plotting
y pos.
z p
os.
(b) 3-D plotting
Fig. 14 Depth control with a PID controller
Course keeping/changing with PID controller
(Fig. 15);
0 50 100 150 200 250 300-20
-10
0
10
20Course Keeping and Changing
Inpu
t 1
[V]
0 50 100 150 200 250 300-20
-10
0
10
20
Time [s]
Inpu
t 2
[V]
0 50 100 150 200 250 3000
20
40
60
80Course Keeping and Changing
Yaw
(de
g)
0 50 100 150 200 250 300-10
0
10
20
Time (s)
Yaw
rate
(de
g/s)
Fig. 15 Course keeping and changing manoeuvres
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5. Experiments for AMC ROV/AUV-3 Before conducting experiments with model-scaled
ROV/AUV, it is important to design the experiments
using the mathematical model-based simulators
described in Section 4.
At the AMC experiments to test the above control
algorithms with AMC ROV/AUV-3 can be conducted
in the Circulating Water Channel (CWC), the Model
Test Basin (MTB) and the Survival Pool. The CWC is
the best option with a 2.5 m depth as it is possible to
observe the vehicle during experiments. Fig. 16
shows the CWC and its arrangement.
Fi.g 16 The CWC and its arrangement
It is planned to install a PC\104 target PC and
electronics on the AMC’s vehicle. The target
computer is connected to the onshore host computer
via an Ethernet cable. The host PC is installed with
control programmes developed using software such as
MATLAB / Simulink / Real-time Workshop and RT-
LAB software.
Fi.g 17 Target and host computers and software
Control hardware and software will be developed in
two stages as shown below:
Stage 1: ROV (PC\104, Ethernet connection);
Stage 2: AUV (Microcontroller, Ethernet or
Wireless connection).
The following experiments are planned for each stage:
depth zigzag test (yaw is kept constant);
depth control test;
course keeping and changing tests;
yaw zigzag test (depth is kept constant);
yaw turning circle test (depth is kept constant);
and
trajectory tracking control tests.
6. Conclusions The paper has described the:
reference frames for description of ROV/AUV
kinematics and kinetics;
development of mathematical models (4-DOF
and 3-DOF) of the AMC ROV/AUV-3 based
on relevant theory;
development of simulation programs and
design of experiments for various scenarios;
including: open-loop manoeuvres and closed-
loop control manoeuvres with PID control law;
AMC experimental facilities; and
computer simulation results showing the
feasibility of the control algorithms for various
manoeuvres of the AMC ROV/AUV.
The following recommendations are proposed for
future work:
conduct experiments in the CWC, Survival
Pool or Model Test Basin;
analyse data from the experiments and verify
the mathematical models;
use CFD simulation method for modelling;
use experimental system identification
methods and experimental data for estimation
of hydrodynamic coefficients;
determine coefficients of the vehicle; and
develop 3D trajectory tracking control
systems.
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Biography
Dr. Hung Nguyen is a lecturer
in Marine Control Engineering
at National Centre for
Maritime Engineering and
Hydrodynamics, Australian
Maritime College, Australia.
He obtained his BE degree in
Nautical Science at Vietnam
Maritime University in 1991,
then he worked as a lecturer
there until 1995. He
completed the MSc in Marine Systems Engineering in
1998 at Tokyo University of Marine Science and
Technology and then the PhD degree in Marine
Control Engineering at the same university in 2001.
During April 2001 to July 2002 he worked as a
research and development engineer at Fieldtech Co.
Ltd., a civil engineering related nuclear instrument
manufacturing company, in Japan. He moved to the
Australian Maritime College, Australia in August
2002. His research interests include guidance,
navigation and control of marine vehicles, self-tuning
and optimal control, recursive system identification,
real-time control and hardware-in-the-loop simulation
of marine vehicles and dynamics of marine vehicles.
Mr. Riaan Pienaar is a fourth
year engineering student. He
has a special interest in
Subsea Engineering and hence
decided to study Ocean
Engineering at the Australian
Maritime College. He also has
a keen interest in UUVs and
for this reason chose to
complete a final year project
entitled “Simulation and
Modelling of ROVs and AUVs”. Riaan is now about
to graduate and enter into the offshore engineering
industry.
Dr Dev Ranmuthugala is the
Associate Dean, Teaching &
Learning, and Associate
Professor in Maritime
Engineering at the Australian
Maritime College, University
of Tasmania. He has also
served as Head of Department
in Maritime Engineering and
Vessel Operations over the
past 15 years. Prior to joining
AMC, he worked as a marine engineer and in the
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design and sales of piping systems. His research
includes: experimental and computational fluid
dynamics to investigate the hydrodynamic
characteristics of underwater vehicles, behaviour of
submarines operating near the free surface, stability of
surfaced submarines, towed underwater vehicle
systems, and maritime engineering education.
Mr. William West jointed the
Australian Army as a Fitter
and Turner when awarded
Apprentice of the Year by
BHP and Ansett Australia in
1979. He worked on several
projects as: commissioning
HMAS Tobruk and Marine
Engineering. On discharge he
began work with Caterpillar
(South Australia) as an
Industrial Engines Technician where he assembled
and maintained diesel powered generators for the oil
& gas sector. In 1986 he returned to Western
Australia; employed as a Mechanic, Maritime Aids
(Australian Maritime Safety Authority) upgrading,
repairing and surveying lighthouses. On completing
his engineering diplomas’ in Mechanical and
Industrial Fluid Power, he took employment with
EMS Services (WA) as a specialist in naval
hydraulics. In 2005 he commenced study at the
Australian Maritime College (AMC) toward his
degree in Engineering (Marine and Offshore
Systems). Graduating in 2009 he took casual work
with AMC to design and build the ROV/AUV used in
this paper for the purposes of observation and
academic research.
Appendix A1. Numerical values of the 4DOF Mathematical
Model for AMC ROV/AUV-3
Table 2 Numerical values of ROV/AUV parameters
m [kg] 17.1 Iz [kgm2] 24.7
l [m] 0.2225 g [m/s2] 9.81
uX 26.0 vY 186.4
wZ 65.95 rN 3.704
u uX 139.2
v vY 53.5
w wZ 79.3
r rN 0.0
k 0.107
A2. 3-DOF Model
Assumptions for modeling AMC ROV/AUV-3 are
[20]:
the ROV/AUV operates at low speeds;
there are no couplings between the six degrees
of freedom;
the vehicle does not develop an angle of trim
or roll during any manoeuvres;
when manoeuvring the sway velocity is
negligible; and
the influence from disturbances such as current
or waves are negligible.
The 3-DOF model of AMC ROV/AUV-3 is
summarized as follows [2][6][20]:
Mν Dν τ (12)
where τ Bu ;
u
w
r
ν ;
u
w
z r
m X 0 0
0 m Z 0
0 0 I N
M ;
u u
w w
r r
X u 0 0
0 Z w 0
0 0 N r
D ;
k k 0
0 0 k
lk lk 0
B ;
and T
1 2 3v v vu .
A3. An Overview of Acoustic Underwater
Positioning and Navigation Systems
This appendix outlines hydroacoustic positioning and
navigation systems as recommended by the reviewers.
One of the great challenges in control and operation
of ROVs/AUVs is the difficulty in underwater data
communication, positioning and navigation. Radio
frequency (RF) wave and wireless transmission
underwater is very weak, so RF navigation systems
like GNSS/D-GNSS and wireless communication
systems are not applicable in underwater vehicles.
Underwater acoustic positioning and navigation
methods help to control and operate ROVs/AUVs.
The main elements of a hydroacoustic positioning and
navigation system as shown in Fig. A1 include a
transmitter (transducer), receiver (transponder), signal
processing and corrections, incorporation of
peripheral data, display of position and some form of
noise and interference mitigation.
Fig. A1 Illustration of hydroacoustic principles (courtesy of
Kongsberg)
A signal (pulse) is sent from the transducer, and is
aimed towards the seabed transponder. This pulse
activates the transponder, which responds
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immediately to the vessel transducer. The transducer,
with corresponding electronics, calculates an accurate
position of the transponder relative to the vessel
[20][21]. Transmission and reception of acoustic
pulses are to track or position a limited number of
objects, both static and mobile [27].
According to Kongsberg Maritime [20], there are
several typical problems for underwater positioning
and navigation. Sound waves do not follow a straight
path. Deflection occurs when the sound passes
through different thermo clines in the sea. Thermo
clines are a result of differences in temperature and
salinity. The velocity of sound varies accordingly to
these factors, and shadow zones can occur. Another
problem with sound in water is noise generated from
the vessel itself and surrounding objects.
A3.1 Operating Principles
Underwater acoustic positioning and navigation
systems use different principles for measurements and
calculations below:
super short baseline (SSBL);
short baseline (SBL);
long baseline (LBL);
multi-user long baseline (MULBL); and
combined mode system.
A3.1.1 SSBL - Super Short Baseline
The calculation of positioning is based on range, and
on vertical and horizontal angle measurements, from a
single multi element transducer. The system (as
shown in Fig. A2) provides three-dimensional
transponder positions relative to the vessel [21].
Fig. A2 Super short baseline principle [24]
A3.1.2 SBL - Short Baseline
The calculation of position is based on range, and
vertical and horizontal angle measurements from a
minimum of three hull mounted transducers. The
system provides three-dimensional transponder
positions relative to the vessel [21] (see Fig. A3).
A3.1.3 LBL - Long Baseline
The calculation of position is based on range
measurements only. The vessel is positioned relative
to a calibrated array of transponders [21] as shown in
Fig. A4.
Fig. A3 Short baseline principle [24]
Fig. A4 Long baseline principle [24]
Advantages and disadvantages of SSBL, SBL and
LBL methods are given in Table 2.
Table 2 Advantages and disadvantages of SSBL, SBL
and LBL systems [27]
System Advantages Disadvantages
SSBL Good potential accuracy
Requires only a single
subsea pinger or
transponder
One time calibration
Highest noise
susceptibility
Accuracy dependent on
shipboard VRU (vertical
reference unit)
SBL Good potential accuracy
Requires only a single
subsea pinger
One time calibration
Accuracy dependent on
shipboard VRU and
heading sensor/gyro
compass
Multiple hydrophones
required through the hull
LBL Highest potential
accuracy
Accuracy preserved over
wider operating area
One hydrophone needed
Redundant data for
statistical testing/quality
control
Requires multiple
subsea/seabed
transponders
Update intervals long
compared to SBL/SSBL
systems
Need to redeploy and
recalibrate at each site
A3.1.4 Combined Mode Systems
Any combination of the three principles above secures
flexibility as well as a high degree of redundancy and
accuracy [21]. Combined systems come in many
varieties below:
long and super short baseline;
long and short baseline;
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short and super shot baseline; and
long, short, super short baseline.
A3.1.5 Multi-user Long Base Line System
The long base line system is extended to multi-users.
A transponder array is deployed and calibrated using
subsea baseline measurements, or run time
calibration. The transponder array must be deployed
in such a way that one of the transponders in the array
has communication with all the other transponders in
the array. This transponder is used as a Master in the
positioning phase. The other transponders are called
Slaves. See Fig. A5.
The Master transponder acts as a beacon. It starts a
positioning sequence by performing the steps below
[25]:
1. the Master interrogates the Slaves in the array
by transmitting the common LBL interrogation
channel to them;
2. after “a turn-around” delay from its own
interrogation, the Master transmits the
individual transponder channel to be received
by the vessels/ROVs/AUVs positioned in the
array; and
3. each Slave transponder receives the
interrogation from the Master beacon, and
transmits its individual reply channels after a
turn-around array.
Fig. A5 Multi-user long baseline principle [21]
If the Slave misses an interrogation from the Master,
it will still reply because it knows the position update
rate. The same principle may be used to save battery
for the Master. The Master may be programmed to
send an interrogation with lower rate, and the Slaves
will use this interrogation to adjust its timing and still
send pulses at the position update rate [25].
The calculation of the position is based on the
measured differences in range between the
transponders in the array. In addition, any measured
angles towards the transponder will be used. Together
with the known coordinates of each transponder, this
is enough to calculate position. Compared to the
standard LBL, the MULBL needs one more
transponder in the array. All vessels that are going to
use the MULBL array need the coordinates of the
transponders and the channel numbers. These data are
distributed on a file [25].
A3.2 Hydroacoustic Aided Inertial Navigation
System
There are many position reference systems that can be
used for marine vehicles. But when a vessel is alone
in the open ocean far way from shore it is only the
satellite based GNSS and the seabed transponder
based hydroacoustic position reference system that
can give reliable reference position [22]. Fig. A7
shows various position reference systems that can be
used for a vessel.
It is ideal to combine acoustic and inertial positioning
principles because they have complementary
qualities. The underwater acoustic positioning and
navigation system itself is characterised by relatively
high and evenly distributed noise and no drift in the
position, while inertial positioning has very low short-
term noise and relatively large drift in the position
over time [22].
Based on the combined acoustic and inertial
positioning principles a hydroacoustic aided inertial
navigation (HAIN) system has been proven its highly
reliable reference position. Main advantages of the
HAIN system are:
Fig. A7 Various position reference systems for a marine
vehicle [22][26]
improved acoustic position accuracy
higher position update rate
extends operational depth capabilities
longer transponder-battery lifetime; and
position update during acoustic drop-out.
Slave 1 Slave 2
Slave 3
Slave 4
Master
ROV/AUV
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