船舶与海洋工程中英文对照外文翻译文献.docx

船舶与海洋工程中英文对照外文翻译文献.docx

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船舶与海洋工程中英文对照外文翻译文献

中英文资料翻译

ASimplePredictionFormulaofRollDampingofConventionalCargoShipsontheBasisoflkeda'sMethodandItsLimitation

Sincetherolldampingofshipshassignificanteffectsofviscosity,itisdifficulttocalculateittheoretically.Therefore,experimentalresultsorsomepredictionmethodsareusedtogettherolldampingindesignstageofships.Amongsomepredictionmethods,Ikeda’soneiswidelyusedinmanyshipmotioncomputerprograms.Usingthemethod,therolldampingofvariousshiphullswithvariousbilgekeelscanbecalculatedtoinvestigateitscharacteristics.Tocalculatetheroildampingofeachship,detaileddataoftheshipareneededtoinput.Therefore,asimplerpredictionmethodisexpectedinprimarydesignstage.SuchasimplemethodmustbeusefultovalidatetheresultsobtainedbyacomputercodetopredictitonthebasisofIkeda，smethod,too.OnthebasisofthepredictedrolldampingbyIkeda’smethodforvariousships,averysimplepredictionformulaoftherolldampingofshipsisdeducedinthepresentpaper.Shiphullformsaresystematicallychangedbychanginglength,beam,draft,mid-shipsectionalcoefficientandprismaticcoefficient.Itisfound,however,thatthissimpleformulacannotbeusedforshipsthathavehighpositionofthecenterofgravity.Amodifiedmethodtoimproveaccuracyforsuchshipsisproposed.

Keywords:

Rolldamping,simplepredictionformula,wavecomponent,eddycomponent,bilgekeelcomponent.

Introduction

In1970s,stripmethodsforpredictingshipmotionsin5-degreeoffreedomsinwaveshavebeenestablished.Themethodsarebasedonpotentialflowtheories（Ursell-Tasaimethod,sourcedistributionmethodandsoon）,andcanpredictpitch,heave,swayandyawmotionsofshipsinwavesinfairlygoodaccuracy.Inrollmotion,however,thestripmethodsdonotworkwellbecauseofsignificantviscouseffectsontherolldamping.Therefore,someempiricalformulasorexperimentaldataareusedtopredicttherolldampinginthestripmethods.

Toimprovethepredictionofrollmotionsbythesestripmethods,oneoftheauthorscarriedoutaresearchprojecttodeveloparolldampingpredictionmethodwhichhasthesameconceptandthesameorderofaccuracyasthestripmethodswhicharebasedonhydrodynamicforcesactingonstrips.ThereviewofthepredictionmethodwasmadebyHimeno[5]andIkeda[6，7]withthecomputerprogram.

Thepredictionmethod,whichisnowcalledIkeda’smethod,dividestherolldampingintothefrictional（BF）,thewave（Bw），theeddy（Be）andthebilgekeel（Bbk）componentsatzeroforwardspeed,andatforwardspeed,thelift（Bi）isadded.Increasesofwaveandfrictioncomponentsduetoadvancespeedarealsocorrectedonthebasisofexperimentalresults.ThentherolldampingcoefficientB44（=rolldampingmoment（kgfm）/rollangularvelocity（rad/sec））canbeexpressedasfollows:

B44Bbk

（1）

Atzeroforwardspeed,eachcomponentexceptthefrictionandliftcomponentsarepredictedforeachcrosssectionwithunitlengthandthepredictedvaluesaresummedupalongtheshiplength.ThefrictioncomponentispredictedbyKato’sformulaforathree-dimensionalshipshape.Modificationfunctionsforpredictingtheforwardspeedeffectsontherolldampingcomponentsaredevelopedforthefriction,waveandeddycomponents.Thecomputerprogramofthemethodwaspublished,andthemethodhasbeenwidelyused.

Forthese30years,theoriginalIkeda’smethoddevelopedforconventionalcargoshipshasbeenimprovedtoapplymanykindsofships,forexamples,moreslenderandroundships,fishingboats,barges,shipswithskegsandsoon.Theoriginalmethodisalsowidelyused.However,sometimes,differentconclusionsofrollmotionswerederivedeventhoughthesameIkeda’smethodwasusedinthecalculations.Then,tochecktheaccuracyofthecomputerprogramsofthesameIkeda’smethod,amoresimplepredictionmethodwiththealmostsameaccuracyastheIkeda’soriginalonehasbeenexpectedtobedeveloped.Itissaidthatindesignstagesofships,Ikeda’smethodistoocomplicatedtouse.Tomeettheseneeds,asimplerolldampingpredictionmethodwasdeducedbyusingregressionanalysis[8].

PreviousPredictionFormula

Thesimplepredictionformulaproposedinpreviouspapercannotbeusedformodemshipsthathavehighpositionofcenterofgravityorlongnaturalrollperiodsuchaslargepassengershipswithrelativelyflathullshape.Inordertoinvestigateitslimitation,theauthorscomparedtheresultofthispredictionmethodwithoriginalIkeda’sonewhileoutofitscalculatinglimitation.Fig.1showstheresultofthecomparisonwiththeirmethodofrolldamping.Theupperoneisontheconditionthatthecenterofgravityislowandtheloweroneontheconditionthatthecenterofgravityishigh.

Fromthisfigur