Abstract：This paperpresentssomeexperimentalresultsaboutPositionMooring(PM)systemappliedto the barge ship。 In PM operation, the station keeping in surge,swayofvesselisprovidedbythe mooring system。 In this paper, a system, consisting of a barge vessel and mooring lines, is mathematically modeled。 The position 82901 andorientationofvesseliscontrolledbychangingthetensionsinthemooringlines。The PID control strategy is applied to evaluate the efficiency of proposed system。 Experimental result which corresponds to the applied control strategy is presented and discussed。

KeyWords：PositioningMooring,BargeShip,Tension, PID

1。Introduction

In recent years, there havebeenincreasing activities which relate to oil exploration and exploitationaswellasoffshoreapplications such thatproductionandpipelaying(Fig。1)。

To increase the safety and efficiency of these purposes,theoffshorevesselmustbesatisfied about station keeping operation wheretheposition and orientation of vessel is keptintheacceptable area。Theapproachofstationkeepingis DP or PM。

The DP system exclusivelyusesthrustersto control thepositionandheadingofvessel。It is reallyefficientfordeepwateroperation。 In contract to DP, in the PMsystem,thevessel’s positioniskeepbythemooring lines。

The mooring system basically compensates for slowly-varying disturbances。 In the normal weather condition, PM system is considered as the passive control system, and the tension of mooringlines should be controlledtoensurethepositionaswell as to prevent the linebreakageinthe hard disturbanceconditions。ThePMisthe most efficient for moored vessels in shallow water with reducing the operational cost and risk。 Several

controlstrategiesformodelingandPMcontrol wereproposed1~4)。

Inthereference[1],thePMwasmodeledon the basis of mooring line tension characteristic by solving the catenary equation。 The LQG controller design of an automatic thruster assisted position mooring system was also studied and the line

breakage compensation withfeed-forwardcontrol wasrecommended。AamoandFossen2,3)developed

which suspended in water and proposed a passive controller to reduce thefuelconsumptionby adjustingmooringlines’ stiffness。

Nguyen and Sorensen4) presented the switching control strategyforthruster-assistedposition mooring。 Depend on theenvironmentaland operational conditions, a supervisor control was adopted to facilitate the automatic switching for heading, damping, restoring andmeanforce controllersofPMsystem。

In this study, the vessel isconsideredasbarge ship。Itmeansthatthethrustersarenot equipped inthevessel。Thestationkeepingoperation is donebyusingPMsystemwith4mooringlines。

Thetensionsofmooringlinesaremeasured

low-frequency (LF)andwavefrequency(WF) model。TheWFmodelaccountsthemotions due to the first-order wave disturbance, where theLF modelprimarilyconsiderstheeffect of second-order mean and slow varyingwave,current and windload。HoweverinPMsystem,theeffect ofWFmotionisquitesmallandcanbe ignored。

The 3 DOFlowfrequencymotionsinsurge, sway and yaw of floating vessel are formulated as follows:

η& = R(  )v,

throughload-cellsattachedatwallof thebasin and each winch system。Foursailwinchesinstalled on the vessel are used to make actualcontrol

Mv&  CRB (v)v  CA (vr )vr

D(vr ) G(η) τ wave 2 + τ windτmoorτthr ,

(1)

forces/changeoftensionsbypulling or releasing the lines。 The PID control strategy is appliedto evaluate an efficiency of the proposedideaand control system。Especially,allresultsaretobe madefromexperimentalstudyoperatedonthe water pool。

where   ∈   representsinertial

position   and heading angle  in the earth fixed coordinate frame and      ∈   describessurge,sway,andyaw rate ofship motion in the body fixed coordinate frame。 The rotation matrix in heading direction  describesthekinematicequationofmotion;thatis