Design of Autonomous Underwater Vehicle

8/11/2019 Design of Autonomous Underwater Vehicle

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International Journal of Advanced Robotic Systems, www.intechweb.orgVol. 8, No. 1 (2011) ISSN 1729-8806, pp 131-139 www.intechopen.com

Design of AutonomousUnderwater Vehicle

Tadahiro Hyakudome

Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Japan

AbstractThereare concernsabout the impact thatglobal

warmingwill have on our environment, andwhichwill

inevitably result in expanding deserts and rising water

levels. While a lot of underwater vehicles are utilized,

AUVs(AutonomousUnderwaterVehicle)wereconsidered

andchosen,

as

the

most

suitable

tool

for

conduction

survey

concerning these global environmental problems. AUVs

can comprehensive surveybecause the vehicle does not

havetobeconnectedtothesupportvesselbytethercable.

Whensuchunderwatervehiclesaremade,itisnecessaryto

consideraboutthefollowingthings.1)SeawaterandWater

Pressure Environment, 2) Sink, 3) There are no Gas or

Battery Charge Stations, 4) Global Positioning System

cannotuse,5)Radiowavescannotuse.Inthepaper,outline

ofaboveandhowdealaboutitareexplained.

1.Introduction

Theoceanoccupiedapproximately71%ofsurfaceof the

earthstillhavealotofunknownparts.Thereforevarious

studiesanddevelopmentabouttheoceansuchasmarine

environment, submarine earthquake, ocean life,marine

resources research and so on are carried out. The

collectionofoceandatabysurveyandobservationinthe

actual sea is indispensable for the studies and the

development. Because the ocean has low transparency

andcannotobservethewholedeepseaindetailfromthe

surface, so, survey andobservationwith the ship isnot

enough.However

the

water

pressure

cannot

step

into

the

deep sea easily because 1 atmospheric pressure is

increasingevery10mdiving.

Various underwater apparatuses such as manned

submersible,unmannedunderwatervehicleandsoonare

developedastoolstosurveyandobservationthedeepsea

since the Bathyscape inventedby Prof.Auguste Piccard

was launched in1948.Themanned submersibles suchas

ALVIN,NAUTILE,

MIRS

and

SHINKAI6500

are

goodatthevisualobservationandsamplinginsmallrange.

The towed vehicles are good at wide area survey. The

RemotelyOperatedVehicles (ROVs)aregoodatdetailed

observationandsamplinginsmallrange.TheAutonomous

UnderwaterVehicles(AUVs)suchasAutosub,Hugin,

ThesusandURASHIMAandsoonaregoodatwide

areadetailedsurveybecausethevehiclesdoesnothaveto

beconnectedtothesupportvesselbytethercableandcan

closetoseafloor.ThedevelopmentofAUVsisenabledwith

recent advanced computing and other various advanced

technologiesshowninfigure1.

Figure 1. The Elemental Technologies for Autonomous

UnderwaterVehicle


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132 International Journal of Advanced Robotic Systems, Vol. 8, No. 1 (2011)

It is necessary to consider about following things on

developing Autonomous Underwater Vehicle: 1)

Seawater andWater Pressure Environment, 2) Sink, 3)

There isNo Gas or Battery Charge Stations, 4) Global

PositioningSystemCannotUse,5)RadioWavesCannot

Useand

6)

Autonomous.

2.SeaWaterandWaterPressureEnvironment

The ocean is the environment that, as you know, filled

withseawater.Becauseviscosityofseawater ishigh, the

oceanishardtomoveincomparisonwiththeatmosphere.

And the remarkable characteristic of the ocean is the

environmentwhere1atmosphericpressure increasesby

every 10 meters diving. Therefore, the water pressure

growsbigsoastogointothedeepseaandwillincrease

strongexternalforceasthingsaredestroyed.

Allof

underwater

vehicles

are

controlled

by

electronics.

However, the elements of most of electronics are not

exposedtoseawatertoshortcircuit.Inadditionthereare

theelementsofelectronicsbrokenbyhighwaterpressure.

Therefore,solidpressurevesselsarenecessarytousethe

electronics in underwater. The pressure vessels are

required tobe enough strong forwater pressure in the

workingdepth, lightweight,not corroded and so on.A

cylindrical shape or aball type ismost suitable for the

shapeofthepressurevessel.Thewaterpressureincreases

according to depth, and so the hull of pressure vessel

needstoincreasethicknesstoaddtostrengthdepending

on

depth.

However

the

strong

pressure

vessels

become

veryheavyweight.Itisnotgoodwithanaspectofenergy

efficiencyforadeepandlongcruisingrangeunderwater

vehiclesothatthepressurevesselsholdabigpartofthe

weightof thebody.Therefore lightandstrong structure

materialforpressurevesselisimportant.

Generally, Aluminum alloy, Titanium alloy and High

TensileStrengthSteelareusedasamaterialofpressure

vessel inJAMSTEC.Thealuminumalloy is lightweight,

high strength, reasonablevalue,but surface treatment is

necessarytouseitinthesea.Thealuminumalloyhasthe

following characteristic: the specific gravity is 2.7, good

workability, not become magnetized, resists low

temperature,easy

to

weld

and

so

on.

Because

navigation

systemsarenotinfluenced,itisgoodthatthealuminum

alloy does notbecomemagnetized. It is important that

heatconductivityofthealuminumalloyisgoodbecause

ofheatradiationoftheelectronicsinthepressurevessel.

Thealuminumalloyhasvariouskindsfrom1000seriesto

8000 series. 5000, 6000 or 7000 series of the aluminum

alloy is mainly used in JAMSTEC. As for 5000 series

aluminum alloy, the strength is ordinary,but corrosion

resistanceishigh.Asfor7000seriesaluminumalloy,the

strengthishigh,butcorrosionresistanceisordinary.The

performanceof thealuminumalloyof6000 series is the

middleof

5000

series

and

7000series.

Corrosion

measures

are necessary to use the aluminum alloy in the sea.

Effectivemeanstoresistseawaterandcorrosionissurface

treatment.Thesurface treatmentsof thealuminumalloy

are anodizing, TUFRAMR, electrolysis nickel plating,

electroless nickel plating, painting. The TUFRAMR is a

technique to make surface enhancement coating of

GeneralMagnaplate.

The titanium alloy is light weight, high strength,

maintenance free,but expensive.The titaniumalloyhas

thefollowingcharacteristic:thespecificgravityis4.5,high

corrosion resistance, low electric conductivity, low heat

conductance,notbecomesmagnetized, lowworkability.

Particularly,thespecificstrengthoftheTi6Al4Valloyis

thestrongest level.The titaniumalloydoesnotneed the

surfacetreatmentevenifusedinthesea.

Thehightensilestrengthsteelishighstrength,moderate

value, but heavy weight and surface treatment is

necessary touse it in the sea.Thespecificgravityof the

hightensile

strength

steel

is

about

7.9.

The

high

tensile

strengthsteelhasmorethan490Mpatensilestrength.

Thepressurevessel isdesignedwithmaterialsmentioned

above. The parameter that is necessary for the pressure

vesseldesignisbucklingstressandyieldstress,andyield

stressbecomesdominantinthehighpressureenvironment

of thedeep sea.The specificationsof thepressurevessel

design are the maximum working depth, the pressure

vesselinsidediameterandlength,safetyfactors.Anditis

necessarytobeconsideredaboutcorrosionandelectrolytic

corrosion.Themetalcorrosionintheseawatergoesbased

on the electrochemic reaction. The materials are made

surface

treatment

to

protect

against

the

corrosion

so

that

they do not touch the seawater directly. The electrolytic

corrosion is a corrosionphenomenon tooccurwhen two

kindsofdifferentmetalcomesintocontactinseawater.The

highmetals of the ionization tendencymelt in seawater,

and themetalsmeltingbecome quicker in the corrosion

speedthancasealone.Asprotectingagainsttheelectrolytic

corrosion,someinsulatorsuchasresinorrubberisattached

tometalcontactsurface,orsacrificeelectrodesareattached

tometal.

The development of the new type pressure vessel by

differentmaterials iscarriedout toreduce theweightof

the underwater vehicles in JAMSTEC. One of the

materialsis

magnesium

alloy,

and

the

other

is

Super

CarbonFiber. In lateyears,manymagnesiumalloysare

developedasthepartsofcars,aircraftandmobiledevices.

Thespecificgravityofthemagnesiumalloy is1.8that is

about1/3of the titaniumorabout2/3ofaluminum.The

magnesium alloy is the most lightweight in metal

structurematerials,andthespecificstrengthisstrongest.

Thepressurevesselmadebymagnesiumalloyshown in

figure2wasproducedexperimentally,andstrengthofit

was evaluated. The size of it is 90mm inside diameter,

130mmlengthand9mmthickness.Thepressurizationtest

for itwas performedwith hyperbaric chamber.At the

pressurizationtest,

the

shrinkage

of

the

pressure

vessel

wasmeasuredby strain gages.Thewaterpressurewas


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Tadahiro Hyakudome: Design of Autonomous Underwater Vehicle 133

pressurized in 2MPa per minute to 40Mega Pascal,

maintained20minutesat40MPaanddeceasedpressure

in2MPaperminute.Therelationsofwaterpressureand

strain of tube part of the pressure vessel are shown in

figure 3. As a result of pressurization test, it was

confirmedthat

the

pressure

vessel

made

by

magnesium

alloywasnotbrokenbywaterpressuremorethan40Mpa.

There is the possibility that the magnesium alloy

contributestothelightweightingofthevehicle.However,

therearealotofproblemsthatmustbesettledtousethe

magnesium alloy in underwater. The most important

problem is corrosion by seawater and electrochemic

corrosion.

TheSuperCarbonFiber(SCF)isCarbonfiberReinforced

Plastic (CFRP) rod having highmoment ofbending and

highpullingstrengthdeveloped inKyushuUniversity.A

pressurevesselmadebyaluminumalloyisreinforcedwith

SCF.Consumption

of

aluminum

decreases

by

this

method

and can reduce theweightof thepressurevessel.Ahull

thicknessofthealuminumandadiameteroftheSCFwere

calculatedbyfiniteelementanalysis,andapressurevessel

isdesigned.Thehybridpressurevesseltype1isshownin

figure4.The sizeof it is100mm insidediameter,150mm

length and 4mm thickness. The performance of the

prototypepressurevesselwasevaluatedinapressurization

testwith hyperbaric chamber.At the pressurization test,

theshrinkageofthepressurevesselwasmeasuredbystrain

gages. Thewater pressurewas pressurized in 3MPa per

minute.Thetimeseriesofwaterpressureandstrainoftube

part

of

the

pressure

vessel

are

shown

in

figure

5.

At

the

resultofpressurizationtest,thehybridpressurevesseltype

1wasbrokenat58.74Mpa.Here,apressurevesselmadeby

aluminum alloy of the thickness of 4mm is broken in

10Mpa by the calculated result. It was confirmed that

reinforcementwiththeSCFwaseffective.Thesecondunit

wasdesignedagain.Andthehybridpressurevesseltype2

wasproducedexperimentally.Thestrengthofitisgoingto

beevaluated innearfuture.Thehybridpressurevessel is

stillthewayofthedevelopment,andvariousproblemsare

left.

Figure2.ThePrototypePressureVesselmadebyMgAlloy(Tube

Part)

Figure3.TheRelationofWaterPressurev.s.Strain

Figure4.ThePrototypeHybridPressureVesselType1

Figure 5.TheTimeSeriesof theStrainof theHybridPressure

Vessel

3.Sink FattoUnderwaterVehicles?

Thedeepunderwatervehiclesbecameheavyweighteven

ifuse

lightweight

materials

for

frames

and

pressure

vessels.Somematerialsneed tobeable to floataheavy

bodytouseadeepunderwatervehiclelikeaspaceshuttle

many times. Therefore it is necessary to addbuoyancy

materials such as the human fat to a deep underwater

vehicle.

The buoyancy materials include gasoline, wood,

expandable polystyrene and syntactic foam. The

characteristicofthegasolineislighterthanseawaterand

notbrokenbywaterpressurebecauseofliquid.Itsspecific

gravity is around 0.8 from 0.75. However, it is

largecapacity need to use it as thebuoyancymaterial.

Andit

is

flammable.

The

volume

of

gasoline

changes

by

waterpressureandtemperature.Therefore,thehandling


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ofgasoline isdifficult.The characteristicof thewood is

lightweight,cheapness,goodprocessing.However, it is

destroyedby thewater pressure, andweight increases

includingwater.Therefore,thewoodisnotsuitableasa

buoyancy material for the deep sea. The expandable

polystyreneis

super

light.

However,

it

is

compressed

by

water pressure and loses buoyancy. Therefore, the

expandablepolystyrene isnot suitable as amaterial for

thedeepsea.

The syntactic foam consistsofgrassmicroballoonsand

epoxy resin. It has high compressive strength against

waterpressure.Itsspecificgravityisaround0.65from0.3,

anditischosendependingonmaximumworkingdepth

of the vehicles. Thisbuoyancymaterial ismachined in

various forms with a saw or a drill. And it is filled

clearancesofpressurevesselsofthebodylikehumanfat.

4.There

is

No

Gas

or

Battery

Charge

Station

Theunderwaterpower source is one of very important

elementstooperateunderwatervehicleparticularlyAUV

foralongtime.Becausethereisnoenergysupplyplaces

inunderwater.Manyresearchanddevelopmentaboutthe

underwater power source are performed. When the

researchanddevelopmentofthepowersource,following

thingsneedtobeconsidered:smallandlightweight,put

inapressurevesselorresistagainstwaterpressure,work

againstlowwatertemperature,vibration,noise,reliability

and for maintenance. The power source has heaviest

weight

with

the

components

of

the

vehicle.

When

the

powersourcebecomesbiginproportiontothescaleupof

thebody,maneuverabilityandenergyefficiencyworsen.

Therefore it is important that thepower source is small

and light weight. Low vibration and low noise

environment is important not to interfere acoustic

equipments such as observation devices or

communications devices. 1) Primary Batteries, 2)

SecondaryBatteries, 3) InternalCombustionEngines, 4)

ExternalCombustionEngines,5)RadioisotopeBatteries,

6)SmallNuclearReactorsand7)FuelCellsareconsidered

asunderwaterpowersource.1)Theprimarybatteryhas

simple structure consisting of an anode, a cathode and

electrolyte.It

can

expose

to

water

pressure.

It

is

small

and

lightweight. Ithashigh energydensity. It canbeused

once.Theuseoftheprimarybatterytakesrunningcost.It

isusedasapowersupplyforindependentdevicessuchas

transponders. 2) The secondarybattery also has simple

structureconsistofananode,acathodeandelectrolyte.It

also can expose to water pressure. It can be used

repeatedly.Runningcostislow.Ithashighreliability.The

secondary battery must not be overcharged or

overdischarged. The secondary battery for underwater

vehicles includes leadbatteries, silverzincbatteriesand

lithiumionbatteries.Thesecondarybatteryiseasy tobe

treatedand

most

suitable

as

abattery

for

the

deep

underwatervehicle.3)Theclosecycledieselengineisthe

only internal combustion engine in the practical use as

underwaterpowersource.It isrobustforenvironmental

change. It is a reasonable system. Itmustbe put in a

pressure vessel. Protections against vibration and noise

arerequiredtouseitasunderwaterpowersource.4)The

externalcombustion

engine

is

the

system

which

converts

thermalenergyintokineticenergy.Thestirlingengineisa

kindof the external combustion engine.The conversion

efficiency from thermal energy to kinetic energy of the

stirlingengineishigh.Ithassmallvibrationandnoise.It

canworkwithoutdependingonthekindofheatsource.It

cannot response to sudden changes. Itmustbeput ina

pressurevessel.5)The radioisotopeconverts theenergy

that occurred by the nuclear decay of the radioactive

elementintoelectricitybyathermoelectrictransducer.AS

fortheradioisotope,longtermpowersupplyispossible.

Itworkscalmly.Itismaintenancefree.Itmustbeputina

pressurevessel.

6)

As

for

the

small

nuclear

reactor,

longterm power supply is possible. It is suitable for

underwater power source. However, it is difficult to

handle.7)Thefuelcellisakindofelectricgeneratorusing

the chemical reaction of hydrogen combines with

hydrogen. It is able to generate electricitydirectly from

chemical reaction without any combustion or

intermediate steps. There are various kinds of fuel cell,

butthesolidPolymerElectrolyteFuelCell(PEFC)system

is most suitable for underwater power sources. The

researchanddevelopmentof theLithiumionSecondary

BatteryandFuelCellarecarriedoutinJAMSTEC.

At

first,

it

is

the

lithium

ion

secondary

battery.

Electric

Power storage is an important technology for all

equipment of the underwater vehicle because

environmental pressure is high, the temperature is 5

degreesCelsiusorless,andconditionsareunsuitablefor

manychemicalreactionsinthedeepsea.Batterycapacity

is mainly dependent on its mass; this means that the

cruisingrange isproportional to themassofthebattery.

Tosolvethisproblem,ahighenergydensitybatteryand

its enclosuresarebeingdeveloped.Concretely,batteries

are enclosedwithoil, to equate environmentalpressure

and tobe insulated in seawater. This is called the oil

compensatedmethod,andisappliedtovariousbatteries.

Secondarybatteries

that

have

been

put

to

practical

use

in

theseaareshowninFigure6.Typicalcellsareleadacid,

nickelcadmium,silverzincand lithiumion.Thevertical

and horizontal axes in the figure indicate the energy

density in weight and volume respectively. The

Lithiumion battery has many merits more than other

batteriesasfollows:1)Energydensityisveryhigh,thisis

themost important factorwhen choosing abattery, 2)

operating voltage is also high, 3) no need to revitalize

accordingtoitsmemory,4)safety,5)maintenancefree,6)

emitsnogaswhen charging7) longer lifetime than the

otherbatteries.TheoneofactualuseLithiumionbattery

isshown

in

Figure

7.

The

oil

filled

300Ah

Lithium

Ion

batteryforthevehiclewasdevelopedin2000.Thebattery


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has three groups in parallel.One group has 120V and

100Ah.Theenergydensityofthebatteryis150Wh/kg.The

more high energy density Lithiumionbattery is under

developmentnow.

Next,itistheClosedCycleFuelCellsystem.Usually,many

underwatervehicles

used

rechargeable

battery

such

that

thelithiumionbatteryorthesilverzincbatteryforapower

source. However the case of long term working type

untethered underwater vehicle, it needs many electric

powersuppliesinproportiontooperationtime.Toextend

operatingtime,thebatterymustbecomeheavierandlager.

But it makes worse the maneuverability and energy

efficiencyofthevehicle.Sothedevelopmentofthefuelcell

forunderwaterpowersourcesisplanned.Thefuelcellisa

kind of electric generator using the chemical reaction of

hydrogen and oxygen. It is able to generate electricity

directlyfromchemicalreactionwithoutanycombustionor

intermediatesteps.

The

solid

Polymer

Electrolyte

Fuel

Cell

(PEFC) system of the underwater vehicle is shown in

Figure 8. Its system has two stacks of generator cells in

series.As each stack generates 2kW electricity and total

outputis4kW.Amongvariousfuelcellsystemsconsidered,

PEFC system is most suitable for underwater vehicles.

Because of the PEFC system generates electricity at

efficiency over 50% and at low temperature about 60

degrees centigrade. The other kinds of fuel cell system

generate electricity at over 100 degrees centigrade. It is

difficult to handle in an underwater vehicle and does

negative influence on other electrical devices installed in

the

pressure

vessel.

And

though

the

fuel

cell

is

a

kind

of

electric generator,mechanical noise and vibration is very

smallbecausethesystemneednotusingturbine.Inthecase

ofusingtheacoustictelemetryorotheracousticdevices,itis

good in smallnoise circumstance.The fuel cell system for

underwaterpower source is required to closed circle type

because of using environment iswater. Recently, storing

hydrogenwithmetalhydridehas come intopracticaluse.

Themetalhydridecanstorehydrogenatlowpressureandit

iscontrolledquitesimply.Whenthealloychargeshydrogen,

itisanexothermicreaction.Ontheotherhand,discharging

hydrogenisanendothermicreaction.Inthevehicle,theheat

which requires an exothermic reaction as discharging

hydrogenuse

the

exhaust

heat

from

the

fuel

cell.

In

case

of

operation, the fuelcell systemandmetalhydride isput in

eachpressurevessel.Then,thepressurevesselsandoxygen

gastankareputinthevehicle.Theoxygenneedstobestored

because using environment is seawater. And generated

waterisstoredinthebottomofpressurevesselforfuelcell.

The reasons to keep generated water are two. The first

reason isbecausemuchenergy isneedgeneratedwater in

high pressure environment. The second reason is to keep

balanceofweightandbuoyancy. If thegeneratedwater is

releasedoutsideofthevehicle,thebalancechangesandneed

additionalenergytokeepitsdepth.

Basedon

results

obtained

in

sea

trials,

the

research

and

development to improve the performance of fuel cell

system ispushed forwardnow.The fuelcell system for

underwater vehicles must be satisfied high efficiency,

highreliability,perfectlyclosedsystem,smallsystemand

longlife.Aresultobtainedbygenerationexperimentofa

developed cell HGC (High Grade Cell) is shown in

figure9.

The

result

of

past

cell

that

used

as

power

source

of AUV named URASHIMA is also shown for

comparison.Thegenerationexperimentwasoperatedat

300kPaApressure.TheIVcurvesareshowninfigure.In

alltheoperatingcondition(0Ato20A),cellvoltageofthe

HGCwasmoresuperiortothatofURASHIMAscell.

Figure6.VolumeEnergyDensityv.s.WeightEnergyDensityof

SeveralBatteries

Figure7.TheLithiumIonBatteryforAUV

Figure8.TheClosedCycleFuelCellsystemforAUV


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Figure9.TheIVcurvesoftheHGCandURASHIMAscell

5.WhereisTheVehicleNow?

Thepositionalinformationofthevehicleisindispensable

toobtainthemarinedatawiththemeaning.However,the

positionalinformation

with

the

Global

Positioning

System

is not availablebecause radiowaves are not usable in

underwater.Thevehicleitselfcalculatesitspositionusing

InertialNavigationSystem(INS)andvelocitylog,or the

vehicle is informed itspositionbya supportvesselora

transponder with acoustic navigation system. One of

InertialNavigationSystemsisshowninfigure10.TheINS

calculates absolute position of themovingbody in real

time. The Type of the INS applied inJAMSTEC is the

strapdown. The strapdown method is fellow method

that inertia sensors are fixed to the movingbody, the

sensoroutputiscountedbackward,andtherateofchange

isestimated.

The

INS

developing

in

JAMSTEC

is

composedofasensorunitandanarithmeticalunit.The

senor unit is composed of three gyroscopes and three

accelerometers.Thegyroscope isameasuredetectingan

angleandanangularvelocityofanobject.Ithasfivekinds

ofmethodsthatarerategyros,vibratingstructuregyros,

gasrategyros,fiberopticgyrosandringlasergyros.The

rategyrousesaspinningtop.Thevibratingstructuregyro

usestheresonancesuchastuningforks.Asforthegasrate

gyro,gas issprayedon theheat rays inahousing.Heat

raystemperaturedetectsthatsprayiscurvedbyCoriolis

forcewhen the housing turns around.As for the fiber

opticgyro

and

ring

laser

gyro,

laser

beams

is

made

to

go

around by mirrors or in a fiber in the housing. The

phenomenonthattimingsfromtheemissiontoreceiving

of the laser changedwhen thehousing turns around is

used.Amongfivekindsofgyros,theringlasergyroisone

of optical rate gyro that hashigh precision and awide

dynamic range. The arithmetical unit defines the

threedimensional coordinate system inside it (INS

coordinatesystem),andanaccelerometerandagyroare

setoneachaxisofit.Theoutputsoftheaccelerometersare

processedby the coordinate transformmatrixwhich is

constructed by the output from the gyros. These are

integrated

twice.

Consequently,

the

current

absolute

position of themovingbody is calculated. The current

posture of it is calculatedby the coordinate transform

matrix. The coordinate transform matrix expresses the

posture relationshipbetween the INS coordinate system

and theEarthcoordinatesystem.Theseveralalgorithms

to reduce calculations errorof the INS isdeveloping in

JAMSTEC.

Thevehicle

is

capable

of

cruising

dozens

of

times

owing

totheinternalpowersupplysystems.Howeveritisvery

difficultforittocruisewithhighprecisionforalongtime

autonomously,dependent only on the INS,because the

positiondatacalculatedfromINSincludesanerrorfactor,

andtheerrorincreaseswiththepassageoftime.Therefore

thevehiclehasahybridsystemwhichcombinestheINS

and the velocity log. This hybrid system enables the

vehicletogetmoreaccuratepositiondatathanusingonly

the INS. The velocity in underwater is measured by

following four measures, Pitot tube velocity log, rotor

typevelocitylogs,electromagneticvelocitylogs,Doppler

VelocityLogs

(DVLs).

The

Pitot

tube

velocity

log

has

good

accuracy in middle range speed measurement. It is

influenced by turbulence and bubble, and precision

deteriorates.Inaddition,itisaffectedbytemperatureand

density of the seawater. It has some errors when the

vehicle turns.Anything should not attach to its sensor

part.So,thepitottubevelocitylogisnotsuitableforthe

underwater velocity log. The rotor type velocity log is

good in themeasurement of the low speed range. It is

affectedbyturbulence.Theinfluenceoftemperatureand

thedensityoftheseawateronitissmall.Itsmeasurement

accuracy is low. So, the rotor type velocity log is not

suitable

for

the

cruising

type

underwater

vehicles.

The

electromagnetic velocity log has effective ranges from

slight low speed tohigh speed. It ishighlyprecise. It is

affectedbyturbulence.Itisnotinfluencedbytemperature

anddensityoftheseawater.Ithassomeerrorswhenthe

vehicle turns.So, theelectromagneticvelocity log isnot

suitable for the cruising type underwater vehicles. The

Dopplervelocityloghaseffectiverangesfromlowspeed

tohighspeed.Ithassmallinfluenceoftheturbulenceand

smallerrorwhen thevehicle turns.Also, itcanmeasure

against water or seafloor alternatively and correct

influenceoftemperatureandthedensityoftheseawater.

TheDopplerVelocityLogissuitableforthecruisingtype

underwatervehicle.

Figure10.TheInertialNavigationSystem

Accelerometer

Ring Laser Gyro

Inertial

Nvaigation

System


7/9


6.RadioWavesCannotUse

Radiowave is a not usable in the sea. However, it is

necessaryforthevehicletocommunicatewiththesupport

vessel.Theacoustictelemetryistheonlyeffectivemethod

inthe

underwater

communication

method.

So,

the

vehicle

communicates with the support vessel by acoustic

telemetry. There are analog communication and digital

communication for acoustic telemetry. It is digital

communication to have the communication of various

data. The underwater acoustic communicationmethods

are Frequency Shift Keying (FSK), Phase Shift Keying

(PSK), Quadrature Amplitude Modulation (QAM). The

FSKcantransmitdataof1byteastwodifferent(highand

low) frequency.ThePSK can transmitdataof 3byte as

differentphase.TheQAMcantransmitdataof8bytethat

mappedphaseandamplitudeontodifferentsignalpoints.

Forexample,

apicture

shown

in

figure

11

is

transmitted

fromanautonomousunderwatervehicleat3,518mdepth

to the support vessel by using QAM acoustic

communication.Thepicturewas takenbyTVcameraof

thevehicle.Thepicturewastransmittedevery8seconds

by 521 dots (horizontal resolving power) x 224 lines

(verticalscanninglines)byusingqualityprioritymode.

Theunderwateracoustic technologyusing timereversal

communicationpushesforwardastudyof longdistance

communicationsanda longdistanceacousticnavigation

inJAMSTEC.

Figure 11.TV ImageTransmittedviaAcousticTelemetry from

3,518m

7.SmartControlSystem

Asmartcontrolsystemneedforautonomousunderwater

vehiclestocruiseinsafelyandpreciselyforlongtime.The

systemneedstocontrolaboutthedevicessuchasthruster,

INS, rearranging of the information of the vehicle, and

motionofthebody.Thecomputerofthevehicleneedsto

do the information processing of a lot of devices. A

distributedprocessing

system

is

necessary,

so

that

processingdoesnotconcentrateononeCPU.

Ontheotherhand,TheAutonomousunderwatervehicles

canmovefreely,becausetheydonotneedcableforpower

supplyandcommunications.So, thevehiclesareable to

maneuver precisely by a highperformance controller.

JAMSTECs AUV is a vehicle designed for scientific

surveys.These

surveys

require

precise

maneuvering

of

thevehiclefordetailedinvestigations.Thevehicleequips

someacousticobservationdevicessuchassidescansonar,

subbottomprofilerandmultibeamechosounder.These

devices need stable cruising, maintaining depth or

altitude,maintainingdirectionor survey lineand soon.

Tosatisfy thesedemands,anadvancescontrolsystem is

one of the solutions for highperformance

maneuverability.Anaccuratemathematicalmodelbased

on vehicle dynamics is needed for design of the

highperformance controller. The dynamic model of a

vehicle in 6 degrees of freedom is described by two

coordinateframes

as

indicated

in

figure

12.

The

notations

for the motions of the vehicle are described by the

followingvectors:

Tzyxzyx

T

T

MMMFFF

rqpwvu

zyx

,,,,,

,,,,,

,,,,,

(1)

Heredenotes thepositionandorientationvectorwith

coordinates in theearthfixed frame,denotesthelinearand angular velocity vector with coordinates in the

bodyfixedframeand isusedtodescribetheforcesand

momentsacting

on

the

vehicle

in

the

body

fixed

frame.

Thevector H,VTconsistsofhorizontalandverticalrudder deflections H andV, respectively. With thisnotation,thenonlinearequationsofmotionofthevehicle

in6degreesoffreedomaredescribedasfollows.

Dynamicequationsofmotion:

M

(2)

Kinematicequations:

w

v

u

z

y

x

coscoscossinsin

cossinsinsincoscoscossinsinsinsincos

sinsincossincossincoscossinsincoscos

(3)

r

q

p

seccossecsin0

sincos0

tancostansin1

(4)

Where

66

55

44

33

22

11

0000000

0000

0000

000

0000

AImx

AImxmz

AImz

mxAm

mxmzAm

mzAm

M

zzG

yyGG

xxG

G

GG

G

(5)


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prmzrmxqmxrvAmqwAmF GGGx 22

2233 )()(

sin)( gm 22 wXvXR wwvv

+(SteeringforceofRudderandelevator)+Thrust (6)

qrmzpqmxurAmpwAmF GGy )()( 1133 cossin)( gm

|||||| rvYrrYvvYrYvY vrrrvvrv

+(SteeringforceofRudderandelevator) (7)

2 211 22( ) ( )z G G GF m A uq m A vp mx pr mz p mz q

coscos)( gm

|||||| qwZqqZwwZqZwZ wqqqwwqw

+(SteeringforceofRudderandelevator) (8)rumzpwmzvwAAqrAIAIM GGzzyyx )())()(( 33226655

cossin)( gzmz BG

|| ppKrKvK pprv +(SteeringforceofRudderandelevator)+Torque (9)

rvmzqwmzqumxpvmxrpAIAIM GGGGxxzzy ))()(( 4466

sin)(coscos)( gzmzgxmx BGBG

|||||| qwMqqMwwMqMwM wqqqwwqw


rumxpwmxpqAIAIM GGyyxxz ))()(( 5544 cossin)( gxmx BG

|||||| rvNrrNvvNrNvN vrrrvvrv


HereMistheinertiamatrix,misthemassofthevehicle

includingseawaterinfreefloatingspaces,Ixx,IyyandIzzare

momentsof inertia about thebodyfixed each axes,A11,

A22andA33areaddedmassandA44,A55andA66areadded

inertia.[xG,0,yG]Tiscenterofgravity,[xB,0,zB]Tiscenter

of buoyancy. The vehicle motion control system is

designed for themathematicalmodelof thevehicle.The

mathematicalmodel (Eqs. (2) (4)) is linearized about

equilibriumpointssuchasforwardspeedisconstantand

other state variables are zero. The linear system of the

vehicleisobtainedfollowingequation(12).

A BM CM

(12)

Wherethex=[isstatevariable,theu=[nMT,H,V]Tiscontrol inputandyM=[z uvwpq r]T isobservedoutput. Arobustservosystemwithobserverisdesigned

such as shown in figure 13 based on the linear

mathematical model (Eq. (12)). The integral action is

necessary to let the vehicle follow target input. The

observer is used for filter effect.Where thexob is state

observer, theFandFIaregainmatrix, thez isobserved

output,thezcistargetinputandtheeiserrorofzandzc.

Acontrol

purpose

is

to

design

optimal

feedback

gain

stabilizinganerroretozero.Thetechniqueoftheoptimal

regulator isLQI (LinerQuadraticoptimumcontrolwith

Integral action) method. The quadratic performance

functionisfollows:

J eTQEe uTREudt

(13)

Where,QEandREareweightmatrix.

Figure12.TheBodyFixedandTheEarthFixedReferenceFrames

Figure13.TheBlockDiagramforRobustServoControlSystem

withObserver

8.NavigationModes

Theautonomousunderwatervehicleneedstohavesome

navigationmodessuchasautonomousnavigationmode

and acoustic remote control mode for many scientific

surveyrequirements.Theconcept is shown in figure14.

Modesarechosenaccordingtothemissiontype.

Theautonomousnavigationmode:theworkingschedule

is preset on the computer in the vehiclebefore starting

observations.The

schedule

includes

the

cruising

course

andprocedureofobservationdevices.Thesupportvessel

carriesthevehicletotheobservationareaandisusedfor

launching and recovery. The vehicle independently

cruiseswithoutanyinformationfromthesupportvessel.

When the vehicle notices some obstacles along its

programmedcourse,ittakesavoidanceactionbyitself.In

the case of long range cruising, some acoustic

transpondersarearrangedalong the cruising course for

reference. The vehicle can correct its position by

communication with transponders, making positioning

accuracybetter.


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Design of Autonomous Underwater Vehicle

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