A Deep Rov Dolphin 3k

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IEEE JOURNAL OF OCEANIC ENGINEERING, VOL. OE-11, NO. 3, JULY 1986 373

A Deep ROV DOLPHIN 3K: Design andPerform ance AnalysisMASAO NOMOTOAND MUTSUO HATTORI

(Invited Pape r)

Abstruct-DOLPHIN 3K is a. tethered emotely perated ehicle(ROW system for ocean bottom surveys down to a depth of 3300 m. Thesystem will be completed in fiscal year 1986. Thi s paper describes thedesign of the system, and analyzes the maneuverability of the vehicle andthe transmission performance of the optical fiber data communicationsystem.

DI. INTRODUCTION

OLPHIN 3K, a deep remotely operated vehicle (ROV)for ocean bottom surveys, is now under development atJapan Marine Science and Technology Center (JAMSTEC).The depth capability of DOLPHIN 3K is 3300 m, 1300 mdeeper than the maximum operating depth of SHINKAI2000, and maximize the cost effectiveness of its underwaterDOLPHIN 3K will be used for the reconnaissance surveysof the ocean bottom prior to the dive of SHINKAI2000. Oneof the important missions of DOLPHIN 3K is to determine themost interesting diving site for detailed studies by SHINKAI2000, and maximize the cost effeitiveness of its underwateroperations, whose time duration is limited by the capacities ofthe batteries and the life support system. DOLPHIN 3K willalso be used for studies of he ocean bottom where depthsexceed hecapabilityofSHINKAI 2000, andwhere t sdangerous for a manned submersible to approach, such as nearactive volcanoes and steep cliffs.The following new technologiesare applied to the develop-ment of the DOLPHIN 3K system.A . The Use of an Optical Fiber Cable

A thin and flexible tether cable which contains optical ibershasbeen developed. It can be used under severe loadingconditions.B. High Data Rate Data Comm unication System

All information including the video pictures from four TVcameras and image data from an obstacle avoidance sonar isdigitized, multiplexed, and transmitted as optical signals via asingle optical fiber line. The data rate of the uplink transmis-sion to the surface ship is 386.64 MHz. This method allowsthe use of an optical rotary connector, and the installation ofManuscript received February 2, 1986.The authors are with the Japan Marine Science and Technology Center,

2-15 Natsushima-cho, Yokosuka 237, Japan.IEEE Log Number 8608927.

electro-optical (E/O) devices, which are very sensitive totemperature changes, is thereby avoided.C. ow-D ensity Buoyant M aterial

Newbuoyant material developed for DOLPHIN 3K iscomposedof alumina ceramic macrospheres (100 mm indiameter) and syntactic foam [l]. Its specific gravity is 0.42with collapse pressure higher than 50 MPa.D . Stereo TV System

TV pictures from two wide-angle monochromatic camerasplaced at slightly different positions are combined to form aetof three-dimensional images. Synchronized TV signals fromthese cameras are alternately supplied to the CRT monitors.Pictures from the two cameras are separated again by stereoviewing glasses, and the operators can perceive the pictures asthree dimensional.These technologies enhance the functions of RO V systemsas remotely operated probes for the studies of the oceanbottom and as remotely operated work tools.Maneuverability of the vehicle, which is one of the mostimportant factors in evaluating the performance ofROVsystems, was analyzed with use of computer simulationtechniques. The hydrodynamic characteristics of the vehicle,necessary for the simulations of motionsof the vehicle and hetether cable, were determined by hydrodynamic tests of a one-quarter scale model.The analysis of the data transmission system of DOLPHIN3K inhis paper is restricted to the evaluation of thetransmission margins of the optical fiber data communicationsystem, which is thought to be the dominant parameter in thesystem evaluation.II.DESIGNND DESCRIPTIONSF THE DOLPHINK SYSTEMThe DOLPHIN 3K system consists of an underwatervehicle, a tether cable, a cable handling system, and a controlconsole van (Fig. 1). The main characteristics of the DOL-PHIN 3K system are shown in Table I.

A . TheVehicleThe vehicle is rectangular in shapeandcomposedofatitanium framework which encloses and supports all compo-nents.Buoyant material blocks are fixedon he top. Sixhydraulic thrusters with shrouded propellers give the vehiclenecessarymaneuvering capabilities even under high slip

0364-9059/86/0700-0373$01OO O 1986 IEEE


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374 I EEEJOURNAL OF OCEANIC ENGINEERING, OL. OE-11, NO. , JULY 19863 ' 3 . 1 r n 9Dowe r l i n e

Fig. 1 . DOLPHIN 3K system.

TABLE IMAIN CHARACTERISTICS OF DOLPHIh' 3K(1) Dimension(2) Weight(3) Maximum operational depth(4) Payload(5 ) Speedforwardbackwardlateralup and down(6) Thrusters

3 m(L) x 2 m ( W ) X 2 m(H)3300 kg (inar) and - 10 kg (inwater)3300 m150 kg ( m a )3 k n21011.5 knlknelectrohydraulic motorfore-aft 2 thrustersvertical 2 thrusterslateral 2 thrusters

(7) Instrumentation color TV, low light monochromaticstereo TV, TV lights, 35-mm stillcamera CTDV sensors, current meter,bilateral servo manipulator (7 degrees offreedom), grabber (5 degrees offreedom)(8) Navigationquipment obstacle avoidance sonar, acousticdirectioninder,ltitudeonardepthometer, gyrocompass, altitudesensor, angular velocimeter

conditions.A seven-degree-of-freedom master-slave manipu-lator and a five-degree-of-freedomoystick controlled grabberare mounted on he front of the vehicle, and stowed within heframe of the vehicle during search and observation asks. Two

P o w IlneI n s u l a t o r

ODticoi f i b e runacket

tension membersheathW

Fig. 2. Structure of he test cable.

TABLE IICHARACTERISTICSOF THE TEST CABLE

(1) Numberfptical fibers four(2) Type of optical fiber Graded Index(3) Diameter of optical fiber core 50 pm(4) Diameter of optical fiber unit 7.2 mm(5) Resistancefower line 3.38 Q l km (3 phase)28.8 Ql l rm (1 phase)(6)Inner and outer jacket Ethylene Propylene Rubber(7) Tensionemberevlar 49(8) Outer diameter 30 mm(9) Specific gravity 1.25(10) Breaking strength greater than 16.5 tonnes

( - 162 kN)

monochromatic ow light level TV cameras provide stereo-scopic view to enhance the perceptions of the observers andgive precise information of the object size and location. Acolor TV camera (l-in image tube) together with an opticalfiber data communication system provides high-quality (400horizontal TV lines) TV pictures. Hydraulic power for thethrusters, pan and tilt unts of cameras and lights, a manipula-tor, and a grabber is generated by a hydraulic pump drivenby an oil-filled induction motor.B . The Tether Cable and the Data Transmksion SystemAU power is supplied via anE/O tether cable shown in Fig.

2. The cable consists of three main conductors for theinduction motor, four subconductors for electronics, sensors,and the TV lights, an optical fiber unit which contains fouroptical fiber lines, Kevlar strength members, and the nner andouter sheaths. These sheaths protect the cable from waterintrusion and cutting. The outer diameterof he cable is30 mm. The characteristics of the cable are given in Table II.Command and data signals for transmission between hevehicleand the surface ship are digitized, transformed tooptical signals, and transmitted via one of four optical fiberlines, using two wavelengths: 830 nm for the downlink and1300 nm for the uplink (Fig. 3) . The data rate of the uplinktransmission is 400 Mbit/s. Although this is higher than therequired rate for transmitting the data from the vehicle,provision for future application of the high-definition TVsystem is considered. This method uses only one optical fiberline, and allows the use of an optical rotary connector(maximum number of optical rotary connector is two). Thusinstallation of E/O devices which are very sensitive to the


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NOMOTO AN D HATTORI: DEEP RO V "DOLPHIN 3K" 375

TV CAMERA 1 -o*mGy----------lV CAMERA 3 ? m1

ITV CAMERA 4 4PF COD DP ' I I, I

r ----IIIIIIIIII

Fig. 3. DOLPHIN 3K data ransmissionsystem.

TABLE IIIOPTICAL TRANSMISSION SYSTEM

1) UPLINKa)ignals TV signals (4 ch)requencyand 60 Hz to 6 MHz, S/N 48 dBOAS (1 ch) Frequencyand 50 kHz to 1 MHz, S/N 50 dBHydrophone (1 ch) Frequencyand 100 Hz to 20 kHz, S/ N 45 dBvehicletatus (200 byte) 900 kbit/sOptical source 1.3-pm wavelength LDSource power - 7 dBOptical receiver (on board)e-APDMinimumeceivingower -3 9 dBBit 386.64 Mbit/sSampling frequency

b)PCMransmission

TV (NTSColor) 14.32 MHz, 8 bit-A/DOAS 4.77 MHz,0it-A/DHydrophone 0.513 MHz, 8 bit-A/DStatus data2) DOWNLINKa) Signals900 kbit/s

OA S (1 ch) Frequency band 50 kHz-1 MHzCommand data (200 byte) 900 kbit/sOptical source 0.85-pm wavelength LDSource power - 4 dBOpticaleceivervehicle)Minimum receivingower - 6 dBSampling frequency

b) PCM Transmission

OAS 4.77 MHz, 10 bit A/DCommand data 900 kbit/s

change of environmental temperature and O/E devices on the determined from the estimatedmaximumamplitude of thecable winch can be avoided. The characteristics of the data heavingmotionof he surface ship atsea state of 4. Thetransmission system are shown in Table III. motion of theram tensioner isalways monitored, and theC. The Cable Handling System

spring constant sautomaticallyselected so that it operatesaround the center of the stroke. The traction winch is used toThe cable handling system consists of a ram tensioner, a store the cable on the cable winch under constant small tensiontraction winch, a constant tension cable winch, and a gimbal (about 1000N ). To keep the tension constant, the cable winchsuspension sheave. The stroke of the ram tensioner wasautomatically follows themotionsof the traction winch. The


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I

I -3ll-lB2--( BO OFig. 4. Initially designe d

-

vehicle

5001 1

model.

OE-11, NO. , JULY 1986

cable scooled by seawater, sprinkled in the cable winch.vehicle. The damping coefficients of he rotational motionsThese equipments are operated from the control console, as were also obtained in this series of tests.well as from the deck side controller.D. The Controlonsoleodifications of theehicleA . Static H ydrodynam ic Tests and Hyd rodynamic

The vehicle is controlled from the control console, housedin a container house. Two operators, a vehicle pilot and amanipulatorkable winch operator, control the systemandperform the tasks. The positions of the operators are somewhatsimilar to those of airplane pilots or car drivers. Seven CRTmonitors are mountedonhe control console. The mainmonitors for the pilot and the manipulator operator are 20-inhighquality color (line resolution is 550) CRT, and three14-in and three 6-in CRTs are used for auxiliary monitors.The distribution of the video signals, i.e., TV pictures fromthe vehicle and from ondeck cameras, and raphicallydisplayed vehicle status data such as depth, attitude, andposition relative to the surface ship can be selected by theoperators. The mock-up of the control console wascon-structed for the layout planning.

III. HYDRODYNAMICH A R A C T E R ~ S ~ C SF THE VEHICLEThe configuration of the vehicle is of an open-frame typewith buoyant material on its top. The flow around a vehicleof this type is complex, ind it is difficult to estimate itshydrodynamic characteristics by calculations. So, hydrody-namic tests were conducted to determine the derivatives which

are necessary for the evaluations of the maneuverability.Two series of tests were performed. The first series consistsof static hydrodynamic tests in which hydrodynamic deriva-tives due to the translational motions at constant velocities,such as drag coefficient, moment coefficient, etc., wereobtained. In the second series, Planar MotionMechanism(PMM) [2] was used to obtain the hydrodynamic coefficientsdue to the accelerations and angular accelerations of the

The initially designed shape of the vehicle is shown in Fig.4. The frame of the vehicle is made of rectangular pipes andthe buoyant material is rectangularly shaped with sharply cutcorners.The tests were carried out in the circulating water channel inMitsui Engineering& ShipbuildingCo., Ltd. The model usedwas a one-quarter scale model. Force and moment exerted onthe model were measured by a six-component spring balancemounted on the model. The body coordinate system, origin ofwhich is fixed to the center of gravity, is shown in Fig. 5.As the results of the preliminary tests showed, there is nodependence of the hydrodynamic Coefficients on the Reynoldsnumber within the velocity ange from 0.4 to 0.8 m / s ; the testspeed was determined to 0.8 m / s from the consideration of thecapacity of the load cell. The Reynolds number was 3.44 Xlo 5based on V I 3 ,where Vis the volume within theenvelopeof the model.Force andmoment were measured, varying the attitude(angle of attack, angle of yaw, and angle of bank) ofhe modelrelative to the flow direction. The drag coefficients of themodel in the six directions of motion (positive and negativedirections along X, Y, nd 2 axes) shown in Table IV wereall larger than the expected values. Then, it was decided tomodify the shape of the vehicle to refine the hydrodynamiccoefficients. The frame members of rectangular cross sectionwere replaced by those of circular cross section, and the shapeof the buoyant material was modified (Fig. 6 ) . As shown inTable V , drag coefficients of the modifiedmodel in al ldirections were reduced, and especially in upward direction itdropped about 50 percent. Attitude ependences of the


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NOMOTO AND HATTOM:DEEP RO V DOLPHIN 3 K 377U

- x (x-Y P M )

X (z-x P M )

Y

ZFig. 5. Bodycoordinate system.

Fig. 6 . Modified vehicle shape. (Corners of thebuoyant material wererounded, and rectangular tubes were replaced by circular tubes.)

TABLE lVDRAGCOEFFICIENTS OF THE NITIAL MODEL (U = 0.8 ds)

Forward Backward Left Right Upward Downward0.877 0.914 1.218 1.186 2.024 1.999

TABLE VDRAGCOEFFICIENTS OF THE MODIFIED MODEL (U = 0.8 m/s)Forward Backward Left Right Upward Downward0.673 0.743 0.981 0.974 0.809 1.582


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ci d e g )

Fig. 7. Longitudinal hydrodynamic characteristics of the vehicle.

1.5' o i-1.0 t w-1.5-2.0 1

Fig. 8. Lateral hydrodynamic characteristics of the vehicle.

hydrodynamic characteristics of the modified model re shownin Figs. 7 and 8.B . Dynamic Tests

The model was testedn a towtankwith use of PMM. Forceand moment coefficients due to the accelerations and angularaccelerations of the vehicle were obtained in this series oftests. These coefficients were called added masses (includingadded moments of inertia and cross coupling terms such asforce coefficients due to angular accelerations).Force F and momentMI ue to the acceleration and angularacceleration of the vehicle are written in the body coordinatesystem as

where [Mij]s the basic inertia matrix of the vehicle, [Ai j ] sthe added inertia matrix, &!Ind o re the velocity and angularvelocity of the vehicle, respectively, and UR s the velocity ofthe vehicle relative to the fluid. A dot symbolabove a quantitysymbol expresses the partial differentiation with respect totime.Generally, 36 added massesexist. However, from hydrody-namic symmetry,Aij = Aji [3], and if the shape of the vehicleis geometrically symmetric or is nearly symmetric, corres-ponding added masses become nearly ero or negligibly small(e.g.


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NOMOTO AND HATTORI: DEEP ROV DOLPHIN 3K 379TABLE VIDYNAMIC DERIVATIVES OF THE VEHICLE

(1 ) Added Mms Coefficients

0.07 negligible 0.077 negligible 0.131 0.08 0.123 0.085~

(2) Damping Coefficients of Rotational Motions

0.133 0.288 0.243

IV. MANEUVERABILITY OF THE VEHICLEA . Equations of Motion of the Vehicle

To avoid the complexity in expressing the full six-degree-of-freedom equations of motion, the equations are written inthe vector form, as shown below.Translational Motion:

[ M T I ~ + [ A ~ ] ~ R + { [ M R T ] * + [ A R T ] } ~+ o x { [ M T 1 ~ + [ A r l ~ R + ( [ M R T I T + [ A R T I T ) o } = ~

(2)Rotational Motion:

[ M R T I ~ + [ A R T I ~ R + ( [ M R I + [ A R I } ~

+0 x {[MRTI + [A R T] R+ ( [ MR ] [ A R I ) ~ }+ ~ x { [ M , 1 9 + [ M , , 1 = ~ } + ~ ~ X ( [ A , ~ ] ~ - ) X+ [ A R T ] T g } = L (3)

where

[ARTIT=ranspose matrix of [ART]A444546

[ A R ] = A54 A55 A56 -(A64 A65 A66)ff and L are the external force and moment exerted on thevehicle; m, 1, and J are the mass, moment of inertia, andproduct of inertia of the vehicle; and X, ,Z are coordinatesof the center of gravity in the body coordinate system.B . External Forces and Moment

The external force f f is given as the sum of the hydrody-namic force FF, gravitational force FG,thrust f fT , and thetension of the tether cable f fcat the cable termination point.F= f F + F G + F:T+FcN

= ? F f F B + + W + C f f T j + F c (4)i = 1

where FB is the buoyancy, f fw is the weight of the vehicle,f f ~ is the thrust of the ith thruster, and N is the number ofthrusters. The external moment is given similarly as

! ! a = L F + L G + L T + L C+ L F + W B x F B + R W X f f w

N N

i = 1 i = lwhere RB,WW W T j , and Wc are position vectors of he centerof buoyancy, center of gravity, the ith thruster, and cabletermination point relative to the origin of the body coordinatesystem, respectively, as shown in Fig. 9. LE is the momentdue to torque of the ith thruster. It mustbenoted hat asmoment coefficients are derived from the steady-state hydro-dynamic tests, they include the moment terms UR X [AT]&!jRwhich appeared in the equation ofrotationalmotion. Thusthese terms mustbe dropped. Magnitudes of thrust andmoment due to the ith thruster are written as


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Fig. 9. External forces and moments on the vehicle.where ni and Di are rotation speed rps) and diameter, and KTiand KQi are the thrust and torque coefficients of the iththruster.C. Equation of Motion of the Tether Cable

Several kinds of computation methods are available for thestudy of underwater cable dynamics [4]. Some of them treatthe cable as continuous. In this case the equations must beconverted to discrete elements mathematically, with use of amethod such as the Finite Difference Method. Other methodsmodel the cable as composed of cable elements of finitelengths. The methodweused is called the LumpedMassMethod, in which the cable is modeled s a chain of extendablebutunbendingweightless cylinders of finite lengths, andmasses of the cylinders are thought to be concentrated at thejoints (Fig. 10).The joints are treated as completely flexible inour model. Now the equation of motion is derived for the ithconcentrated mass as

= U i - U j - l + F i , for i = l to M-1 (6)where [mi nd [ A ] ; re the basic inertia matrix of the ithconcentrated massand the added inertia matrix of the ithcylinder. X i is the position of the ith mass. Ui is the tension inthe ith cylinder (Fig. 11). As the magnitude of tension in thecable is proportional to extension of the cable, it can beexpressed aswhere E is the Youngs modulus of the cable and Si is thesectional area of the ith cylinder. Wi( = X i + l - Xi) is the

Fig. 10. Simulation model of the tether cable.

Fig. 11. Forces on the it h concenh-ated mass.

position vector from Xi to X i+ and 1,; is the natural length ofthe ith cylinder. The external force5 n the cable is describedin the following section.D . External Forces on the Cable

The external force on the ith mass is thought to be the sumof the gravitational force FGi,which includes the buoyancyforce, and halves the hydrodynamic forces on the ith and(i - 1)th cylinders ITH and 5fi- :

12IS;=- (Ffi+F:~i-l)+F~i. (8)

The exact nature of the hydrodynamic force on cables is notknown, and many kinds of formulation models are proposed[5].As the analysis is three dimensional, we derived the three-dimensional formulation of hydrodynamic force in the vectorform as follows. Hydrodynamic force is resolved into normaland angential components. Each component sassumed todepend only on he velocity component in thatdirection (Fig.12). Now hydrodynamic force on the ith cylinder is written as

where p is the density of the seawater, di is the diameter of theith cylinder, and C, and C,are the normal and tangential dragcoefficients of the cable. U l n j and Uti are the normal andtangential components of the flow velocity o the ith cylinder,calculated from the following equations:

where &!Jc is the velocity of water current relative to the earth.


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NOMOTO AND HATTOM: DEEP ROV DOLPHIN 3K 38 1

Fig. 12. Hydrodynamic force on the itb cylindrical cable element.II8II

Fig. 13 . Upper boundary condition. Position of the upper end of the tethercable is given as a known function of time.E. Boundary Conditionsfor the Calculations of CableDynamics

The boundary conditions are given at the upper and lowerend of the cable. As we assume that the ship motion is known,the position of the upper end of he cable &,= Xact)s givenasa unction of time (Fig. 13). At the lower end, cable isconnected to the vehicle. As the position of the abletermination point in the body coordinate system is Rc (Fig.14), the velocity of the lower end of the cable is given as

X.M=r!!I++cXO. (10)Now M - 1 equations of motion of the concentrated masses(6) and equations of motion of the vehicle (2) and (3) can besolved for given oceanic conditions and ship motions.F. Footprints of the Vehicle

The footprint of the vehicle is defined as the outer boundaryof the operational area of the vehicleon the ocean floor undergiven operational conditions [3]. Equilibrium positions of thevehicle are given as solutionsof (2), (3),and (6 )for @!II j =Bi = 0 and U = o = %i = 0 for i = 1 toM. Because of thelimited capacity of the hydraulic power supply, all thrusterscannot be operated simultaneously at fu l powers. Thereforehydraulic power management s required to optimize thefootprint. Some of the results obtained for vehicle operationsat the depth of3300 m both with and without adepressor arepresented. The cable and vehicle parameters are as follows.1) The tether cableLengthmaximum) 5000m

XywZ

Fig. 14. Lower boundary condition. Position of the lower end of th e tethercableXM s determined from the position and the attitude of the vehicle,which are obtained as solutions of (2) and (3).

Diameter 30 mmWeight in water 1.87 N/mNormal drag 1.2Tangential drag 0.01Youngs modulus 1.372 X 1OO N/m2Added mass coefficients tangential: 0

(= added mass/pVc, normal: 1where Vc is thevolume of the cable)

coefficient (C,,)coefficient (CJ

The vehicleWeight in air 3400 NBuoyancy 3493 NVolumeithinhe 9.66 m 3vehicle envelope ( V )Positions of the externalforce actiona) Cable tension Rc=(;2)=( -0.28 m)

-0.91 mb) Center of gravity

Rw=( :E= E.03 m)-0.1 mc) Center of buoyancy

R B = ( 2 ) = ( -0.37 -0.1mm) .ThrusterDiameters Dl = 4 = 0.428 m

D3 = D 4 = 0.375 mD S = 0 6 = 0.35 m

parameters


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IEEE OURNAL O F OCEANIC E N G m E R I N G , VOL. OE-11, NO. 3, JULY 1986

Maximum torque L 1 = L2 = 121.8 N-mL3 = L4 = 62.33 N-mL5 = L6 = 53.6 N-mTorque KQ1 = KQz = 0.044-0.015 XJcoefficients (&) (forward)

= 0.395 -0.225 XJ

(backward)K B = Kp4 = 0.027KQs = K B = 0.027(downward)= 0.023 (upward)Thrust K n = K T ~ = 0.52-0.6 X Jcoefficients ( K T ) (forward)= 0 . 4 - 0 . 6 X J(backward)K7-3 = K T ~ = 0.37

K n = KT6 = 0.37 (downward)= 0.27 (upward)

where J( = 1URl / nD) is the advance ratio of thevehiclerelative to the fluid.Thruster numbers and their positions are shown in Fig. 15,and their values are listed below.

4 ) The depressorWeightn 600 NDrag area 1.12 m2Cable lengthetween the depressor 300 m.(reference area X drag coefficient)and the vehicle

Calculations were done for the following conditions. It mustbe emphasized that hese conditions correspond to the ultimateoceanic conditions, and usually, vehicle operations should bedone under more moderate conditions:1) Depth 3300 m2) Current velocity distributions See next paragraph.Ocean current profiles are given with two parameters Usand UJD. The current velocity is assumed to decrease from U sat surface to U Dat the depth of500 m (Fig. 16), and is constantbelow 500 m. Current conditions and corresponding resultsare listed in Table W.In these calculations, backward thrust is not used. So, if thefore-and-aft thrusters are reversed, footprints will xtendfurther to the downstream direction. The cable is paid until

Yt IFig. 15. Thruster numbers and their positions and orientations.

the vehicle reaches the bottom within the maximum length.Operational restrictions are also imposed on the calculations.Even though the vehicle could reach a certain point on thebottom, if the equilibrium attitude of the vehicle is notappropriate for operations, the vehicle is thought to be out ofthe operational area. Thus we use the following operationalrestrictions:I Pitch angle < 10"IRoll angle


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NOMOTO A N D HAlTORI: DEEP ROV "DOLPHIN 3 K " 383

TABLEWOCEAN CURRENT CONDITIONS AND CORRESPONDINGRESULTSWithout a depressorith a depressor

4kn0 0.5 kn lkllFig. 17 Fig. 19 Fig. 21Fig. 18 Fig. 20 Fig. 22

4klllkllFig. 23Fig. 24

Fig. 16. Model of the ocean current profile.

XCm)4 3 2 1 0 -1 -2 -3 -4+ 1Gl"7

soow1 SOON 500N

*lY?

3I

DepthC m > = 3300Pi t ch= ?0Max. an IeCdeg)

Fig. 17. Tethercablecatenaries (V, = 0).


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384 JEEE JOURNAL OF OCEANIC ENGINEERLNG, VOL. OE-11, NO. 3, JULY 1986

Deo th Cm l = 3300Max. an g 1e (deg)P i c h = 1QR o l l = 6.185Yau= 0TZ=SOON 2- OOON, ,+ . , I . . . ,. . .I - . . . , . - - . , a , . .I . . .-1 -2 -3 -4*10"3I X(m)

-2-

Fig. 18. Footprints of the vehicle (LID = 0).

X C n l l4 3 2 1 0 -1 -2 -3 -4 1 W 3

* 10"34fq D epth Cm>= 3300Max. an g e (deg)P i t c h = 18Fig. 19. Tether cable catenaries (LID = 0.5 kn).


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NOMOTO AND HATTORI: DEEP ROV "DOLPHIN 3K " 385

*109r\"

. "_..""..x aw=.^^^..

1Fig. 20. Footprints of the vehicle (VD 0.5 kn).

XCm)4 3 2 1 0 -1 -2 -3 -4*10"3

nEN"

Depth ( m ) = 3300Max. a n g l e (deg)P i t c h = 10I

Fig. 21. Tether cable catenaries (UD= 1.0kn).


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EEE JOURNALOF OCEANIC ENGINEERING, VOL. OE-11, O. 3 , JULY 1986

DepthCrnl= 3300Max. an leCdeg)P i t c h = 90R o l l = 1.906Yaw= 0

1i

- I2Fig. 22 . Footprints of the vehicle (UD 1.0 kn).


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NOMOTO A N D HA'ITORI: DEEP RO V "DOLPHIN 3K" 38 7

* 1 D * 3 ::3 ::

n - Dep th Cm)= 3300 1v2. .- Max. ang I e ( d e g ):: Pitch= 102 7: R o l l = 6.165Y a w = 0

1 :.T

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . :: -3 -4 10*33 2 1 0 : . . , . I . . . .. . . I . . . . * . , . . . . I .. , . " ' 8 . *X I m >

-1 ::

-2 7 :

Fig. 24. Footprints of th e vehicle: operation with a depressor(UD=.O kn).depressor and a vehicle cannot be long enough that a vehiclehas comparable operational areas to those withouta depressor.Thus the useof a depressor reduces the operational area of thevehicle in most cases.G . Influence of the Ship Mo tion on the Vehicle

Full equations of motion of theether cable and the vehiclemust be solved to obtain the behavior of the vehicle and thecable in the time domain. Although the initial conditions forthe calculations (positions and velocities of M concentratedmasses, attitude of the vehicle, translational androtationalvelocities of the vehicle atimer = 0) are somewhat arbitrary,the results from the equilibrium calculations were used asinitial values to save computation time. The position of theupper end of the cable was input as sinusoidal functions oftime, and he responses of he cable and hevehicle werecalculated. The calculations were done for the followingoperational conditions:

Amplitude of the 5 m ( P - P )ship heavingAmplitude of the 5 m ( p - p ) in theship surging current directionPeriod 6 sThrusts of the vehicle IFnl = IFrzl = 1265 NIF=( = IF761 = 800 Nothers: 0.The oceanic conditions are the same as those in the footprintcalculations with U = 1 k n . Although the equations are threedimensional, the above conditions are two dimensional. Thusthe results are two dimensional.Fig. 25 shows the tensions in the tether cable at the upper(ship side) and the lower (vehicle side) ends due to pure heaveand pure surge motions of the urface ship. The motions of the

cable and the vehicle are shown in Fig. 26. Fig. 27 shows thefluctuations of cable tensionswhen the vehiclekeeps itsposition and attitude. As can be seen from this figure, if thevehicle is operated under these conditions, quick control oflarge thruster powers is required to keep hepositionandattitude of the vehicle. This seems not realistic. Therefore adepressor should be used in these cases. However, it must beemphasized gainhat the calculations were done underextremely severe oceanic conditions.

V. PERFORMANCE ANALYSIS OF THE DATA RANSMISSIONSYSTEM

Oneof the mostdominant parameters in evaluating theperformance of an optical data transmissionsystem is thetransmission margin above the minimum signal level of theoptical receiver at which the error rate can be kept belowSince DOLPHIN 3K uses the single optical fiber linesystem, all he data gathered in hevehicle are digitized,transformed to serial data, and pulse code modulated (PCM).The data rate of the uplink transmission is 386.64 MHz, andthiss earlyhemaximum data rate for 5000-m datatransmissionwith a GI fiber (Fig. 28). The transmissioncharacteristics of an optical fiber for DOLPHIN 3K is shownin Fig. 29. As can be seen from this figure, the transmis-sion losses for 850- and 1300-nm wavelengths are 2.7 and0.7&/ h,espectively. The calculated transmission marginsare shown in Fig. 30. In these calculations, 3 and 1d3hareused for the transmission losses instead f the above-mentioned values to obtain the safety side estimations. Thetransmission margins are estimated to be 20 dB for both uplinkand downlink,The difficulties in the applicationofoptical fibers toumbilical cable of RO V systems arise from extremely severeloading conditions during the vehicle operations. The cable


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388 IEEE JOURNAL OFOCEANIC ENGINEERING, VOL. OE-11, NO, , JULY 1986

l lo.l R.0.V Side - eavingSurging--

Ship Slde S.V.rStatic Value0 . 1 ! timefa)10 . 7 5 .0 . 8 5 . S O .

Fig.25. Fluctuations ofcable tensions at th e upper and the lower ends dueothe motions of the surface ship.

R.O;V m t io a9.9deg

8.96deg

Fig. 26. Motions of th e variouspoints along the tether cableand the vehicledu e to the. surging motion of the surface ship.


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NOMOTO AND HATTOFU: DEEP ROV 'DOLPHIN 3 K ' 389

100 .1 R.O.V. Side- eaving

Surging--

Shi p Side0. 70 . 1 I I tilmfs)75 . 8 0 . 85 . 90 .Fig. 27. Fluctuations of the cable tension when the position and the attitudeof the vehicle are f ixed.

5 10 2 I kTrmlssion rawFig. 28 . Bandw idth characteristics of a typical optical transmission systemwith a GI optical fiber.

Fig. 29 .Wave leng th pm

Transmission loss of a GI optical fiber used n the DOLPHIN 3Ksystem.

-10

-30

-40

1

Fig. 30. Level diagram of the optical transmission system in DOLPHIN 3K.


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. . . . . . . .

3903~3.15mnODomr I 1ne

E E E JOURNAL OF OCEANIC ENGINEERING, VOL. OE-11, NO. , JULY 1986

2.0

0.5Fig. 31. Structure of theprototype tether cable. Six optical ibers arecontainedin the cavity of the nylontube.They are twisted arounda steel wire.

1100

0

0T E N S I O N ( t)

Fig. 33 . The typical result of the tensile test of the tethercable. Initial valueof the optical transmission loss at zero tension is due mainly to the lowoptical source power.

I \ -73

m

f l0 I1 0 2 0 3 0 ~ 5 0 6 0 7 0 8 0

WTRXTATIC MS3JE WU)Fig. 32 . Hydrostatic pressure test of the tether cable.

suffers hydrostatic pressure, gravitational force, hydrody-namic force, and inertial force due to the motions of the cable,the surface ship, and the vehicle. Simultaneous actions of theseforces make the cable loading complex and heavily fluctuat-ing. Moreover, the cable experiences large side pressure onsheaves in the cable handling equipment. The prototype cable(Fig. 31) was designed and tested [6]. It contains six opticalfibers in the cavity of a nylon tube whichservesas a pressure-resistant housing. The results of the test showed that underhydrostatic pressure, the circumferential distributions of radialcompression force on the nylon tube was not uniform, andbuckling occurred at about 40 MPa. To avoid this bucklingproblem, a plastic spacer was inserted in the nylon tube n the

modified cable which was previously hown in Fig. 2. Variouskinds of tests were performed on the cable samples. Some ofthe results are shown below. Fig. 32 shows the result of thehydrostatic pressure test. The cable was tested in the high-pressure test vessel at JAMSTEC. A 100-m long cable waswoundona eeland instrumented with strain gauges tomeasure both axial and circumferential strains under hydro-static pressures. The optic signals were transmitted via one offour optical fibers through an optical connector, and returnedback into another optical fiber at the end of the cable. Thesignal was taken outof the vessel through an optical connectoragain and fed to the optical power meter. As canbe seen fromFig. 32, influence ofthe hydrostatic pressure on the transmis-sion loss was not observed at pressures below 60 m a . Thetransmission loss began to increase at 60 MPa, and theincrease was accelerated at higher pressure than 60MPa. Thepressure was aised to the maximum (80 MPa)and henlowered. The figure also shows the recovery of the transmis-sion loss, and this ndicates that the optical fiber did not ustainfatal damages. Fig. 33 shows the typical result of the tensiletest. The tensile strain of the cable increases almost linearlywith tension, and the cable broke at about 176 400 N(18 tomes), while serious increase in the optical transmissionloss was not observed. Results of he other tests such as cyclictension test, cyclic bending test, cyclic twisting test, etc. alsoassured the transmission margin of the system under normaloperational conditions. A transmission test with a ful length(5000 m) cable at sea was performed in April 1986.

VI. CONCLUSIONS1) The full equations of combined motions of n ROV and atether cable were derived, and the maneuverability of thevehicle was analyzed.2) The footprints of DOLPHIN 3K were calculated forultimate oceancurrent conditions. The results tell us that whenlarge operation area is desired, vehicle operation without a

depressor is advantageous, and when the ocean current isstrong, use of a depressor can increase the maximumoperatingdepth; however, the operational area is reduced.


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NOMOTO AND HATTORI: DE E P RO V DOLPHIN 3 K 39 13) When he vehicle must be operated with a taut tethercable because of strong ocean current, and asks requireprecise keeping of position andattitude of the vehicle, use of adepressor which decouples the surface ship motion from thevehicle will improve the maneuverability of the vehicle.4) Transmission margin of the optical fiber data transmis-sion system for DOLPHIN 3K was calculated, based on thetransmission characteristicsof the test cable developed for thetether cable of DOLPHIN 3K.5 ) The results of the tensile test and the hydrostatic test ofthe tether cable proved that the cable has enough mechanicalstrength to protect delicate optical fiber lines against severeloads during the vehicle operations.

ACKNOWLEDGMENTThe authors appreciate Y. Kadomoto of Mitsui Engineering& Shipbuilding Co., Ltd. and H. Ishidera of Mitsui OceanDevelopmentand Engineering Co., Ltd. for their help npreparing the manuscript.

REFERENCESM. Hattori, K. Takahashi, and Y. Kadomoto, Present status of ROVsi n JAMSTEC, in Proc. ROV85 (San Diego, CA), Apr. 2-4, 1985,T. B. Booth and R. E. D. Bishop, The planar motion mechanism,Admiralty Experimental Works, 0 Crown Copyright 1973.L. Landweber,Motion of immersedndloating bodies, inHandbook of Fluid Dynamics, V. treeter, Ed. New York:McGraw-Hill, 1961.Y. Chooand M. J . Casarella, Survey of analyticalmethods ordynamic simulation of cable-body system, J . Hydronautics, vol. 7 ,no. 4 , Oct. 1973.

pp. 126-132.

[5] M. J. Casarella and M. Parsons, A survey of investigations on theconfiguration ndmotion of cableystems nder ydrodynamicloading, Marine Tech. SOC.J . , vol. 4, no. 4, Aug. 1970.[6] M. Nomoto,M. Hatton, and T. Aoki,Application of optical fibrecables toseabed survey, in Proc. 0184 (Brighton, U.K.), Mar. 6-9,1984, 0 1 3.5. *Masao Nomoto received the B.S. degree in aero-nautics and the M.S. degreen applied physics romKyushu University in 1971 and 1973, respectively.After that he joined JapanMarine Scienceand Technology Center, Yokosuka, Japan, wherehe is presently an Assistant Senior Scientist in theDeep Sea Technology Department. e isengaged inresearch anddevelopment of remotelyoperatedvehicles.

; Mr Nomoto is a member of the Society of NavalArchitects of Japan.*Mutsuo Hattori received the B.S. and Dr.Sciencedegrees from Tohoku University n 1962 and 1967,respectively.From 1969 to 1972 hewas aLecturertInternationalChristianUniversityandwas also aResearch Staff Member of the Ocean ResearchInstitute, University of Tokyo, Tokyo, Japan. He iscurrently a Senior Scientist in the Deep S e a Tech-nologyDepartmentatJapanMarineScienceandTechnology Center, Yokosuka, Japan. His interestsare in the application of remotely operated vehicles

Dr. Hattori is a member of theGeologicalSociety of Japanand heto marine geological research.Oceanographical Societyof Japan.

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