mô hình hóa, mô phỏng và điều khiển phương tiện ngầm

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 Universi

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

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

u, v, w, p, q, r



ν

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

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],

 





where

  nb  3 3 

3 3



J η

with η 3S3 and ν 3 The angle rotation

matrix n  3 3

b





R Θ is defined in terms of the

principal rotations,

x,



   



  

z,



  

where s=sin(.), c= cos(.) using the zyx-convention,

 

n

b : z, y, x,

or

 

n

b

              

               

The inverse transformation satisfies,



The Euler angle attitude transformation matrix is:

0 s / c c / c



 

1





 

    

90

It should be noted that T Θ is undefined for a pitch angle of o

90

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,

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 =CRB ν CA ν : Coriolis-centripetal matrix (including added mass)

 

D ν : damping matrix

 

g η : vector of gravitational/buoyancy forces and moments

0

g : vector used for pretrimming (ballast control)

τ : vector of control inputs

wind

τ : vector of wind-induced forces and moments wave

τ : 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],

 

0

M ν C ν ν M ν C ν ν D ν ν

where wτwindτwave and νr ν νc (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

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

Height with light 323 mm

Weight in the air 17.1 kg

Fig 2 The 3 rd 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 (u i , 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:

 



Kinetics:

   

where:

x y z

 

 

 



 

 



 

  



u v w r

 

 

 



 

 

 

u

v

w

z r





 

v u



 

u u

v v

w w

r r

0 0 0 0

 

 

 



 

 

 

kl 0 kl



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

 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:

     

d t

dt

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

-1 -0.5 0 0.5 1 -101 -100.5 -100 -99.5 -99

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

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

x pos.

y pos.

Fig 10 Right turn (z(0) = 100 m)

Estimated position and velocities

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

0 20

-1 -0.5

0

0.5

1

-160

-150

-140

-130

-120

-110

-100

x pos.

y pos.

Fig 11 Diving (z(0) = 100 m)

-80 -60 -40

-20

-1 -0.5 0

0.5

1

-100

-90

-80

-70

-60

-50

-40

x pos.

y pos.

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.

Fig 13 Zigzag test (u 3 = 10 V, change in z = 10 m)

 Depth control with PID controller (Fig 14);

-115 -110 -105 -100 -95 -90

-85

Depth Control - 2D Plotting

Time [s]

(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.

(b) 3-D plotting

Fig 14 Depth control with a PID controller

 Course keeping/changing with PID controller

(Fig 15);

-20 -10 0 10 20

Course Keeping and Changing

-20 -10 0 10 20

Time [s]

0 20 40 60 80

Course Keeping and Changing

-10 0 10 20

Time (s)

Fig 15 Course keeping and changing manoeuvres

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

References

[1] Roberts, G.N and Sutton, R (Editors)

Advances in Unmanned Marine Vehicles The

Institute of Electrical Engineers, 2006

[2] Fossen, T.I Nonlinear Modelling and Control

of Underwater Vehicles, PhD Thesis Norwegian Institute of Technology, 1991

[3] Fossen, T.I Handbook of Marine Craft Hydrodynamics and Motion Control John

Wiley and Sons Inc 2011

[4] Fossen, T.I Marine Control Systems – Guidance, Navigation and Control of Ships, Rigs and Underwater Vehicles Marine Cybernetics, Trondheim, Norway, 2002

[5] Fossen, T.I Guidance and Control of Ocean Vehicles John Wiley and Sons, 1994

[6] Wadoo, S.A and Kachoroo, P Autonomous Underwater Vehicles: Modeling, Control Design, and Simulation CRC Press, 2011

[7] Nguyen, H.D Multitask Manoeuvring Systems Using Recursive Optimal Control Algorithms Proceedings of HUT-ICCE 2008, pp 54-59 Hoi

An, Vietnam, 2008

[8] Nguyen, H.D Recursive Identification of Ship Manoeuvring Dynamics and Hydrodynamics Proceedings of EMAC 2007 (ANZIAM), pp 681-697, 2008

[9] Nguyen, H.D Recursive Optimal Manoeuvring Systems for Maritime Search and Rescue Mission, Proceedings of OCEANS'04

MTS/IEEE/TECHNO-OCEAN'04 (OTO’04),

pp 911-918, Kobe, Japan, 2004

[10] West, W.J Remotely Operated Underwater

Vehicle, BE Thesis Australian Maritime

College, UTAS, Launceston, 2009

[11] Gaskin, C.R Design and Development of

ROV/AUV, BE Thesis Australian Maritime

College, UTAS, Launceston, 2000

[12] Woods, R.L and Lawrence, K.L Modeling and

Simulation of Dynamic Systems Prentice-Hall

Inc Upper Saddle River, NJ, 1997

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J.L Dynamic Modeling and Control of

Engineering Systems Cambridge University

Press, 2007

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Force Control of Vehicle-Manipulated Systems,

2nd Edition Springer, 2006

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Explorer class autonomous underwater vehicle

for missions under sea ice, 3rd International

Conference in Ocean Engineering, ICOE 2009,

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presentation, 2009

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Submarine Design Cambridge University Press

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Applications of Autonomous Underwater

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Integrated Navigation Systems Artech House,

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[20] Pienaar, R Simulation and Modelling of ROVs

and AUVs BE Thesis Australian Maritime

College, Launceston, 2011

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Positioning and Navigation Systems HiPAP and

HPR, accessed on 19/11/2011

http://www.km.kongsberg.com/

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Aided Inertial Navigation System – HAIN A

New Reference for Dynamic Positioning

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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

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

u

v

w

u u

v v

w w

r r

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]:

where τ Bu ; u

w r

 

 

  

 

u

w

z r



u u

w w

r r





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

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;

 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 3 Slave 4

Master ROV/AUV