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1、ASimplePredictionFormulaofRollDampingofConventionalCargoShipsontheBasisoflkeda'sMethodandItsLimitationYukiKawahara,KazuyaMaekawaandYoshihoIkedaDepartmentofMarineSystemEngineering,OsakaPrefectureUniversity,Sakai599-8531’JapanAbstract:Sincetherolldampingofshipshassignificanteffectsofviscosity,itisdi
2、fficulttocalculateittheoretically.Therefore,experimentalresultsorsomepredictionmethodsareusedtogettherolldampingindesignstageofships.Amongsomepredictionmethods,Ikeda’soneiswidelyusedinmanyshipmotioncomputerprograms.Usingthemethod,therolldampingofvariousshiphullswithvariousbilgekeelscanbecalculated
3、toinvestigateitscharacteristics.Tocalculatetheroildampingofeachship,detaileddataoftheshipareneededtoinput.Therefore,asimplerpredictionmethodisexpectedinprimarydesignstage.SuchasimplemethodmustbeusefultovalidatetheresultsobtainedbyacomputercodetopredictitonthebasisofIkeda，smethod,too.Onthebasisofth
4、epredictedrolldampingbyIkeda’smethodforvariousships,averysimplepredictionformulaoftherolldampingofshipsisdeducedinthepresentpaper.Shiphullformsaresystematicallychangedbychanginglength,beam,draft,mid-shipsectionalcoefficientandprismaticcoefficient.Itisfound,however,thatthissimpleformulacannotbeused
5、forshipsthathavehighpositionofthecenterofgravity.Amodifiedmethodtoimproveaccuracyforsuchshipsisproposed.Keywords:Rolldamping,simplepredictionformula,wavecomponent,eddycomponent,bilgekeelcomponent.IntroductionIn1970s,stripmethodsforpredictingshipmotionsin5-degreeoffreedomsinwaveshavebeenestablished
6、.Themethodsarebasedonpotentialflowtheories(Ursell-Tasaimethod,sourcedistributionmethodandsoon),andcanpredictpitch,heave,swayandyawmotionsofshipsinwavesinfairlygoodaccuracy.Inrollmotion,however,thestripmethodsdonotworkwellbecauseofsignificantviscouseffectsontherolldamping.Therefore,someempiricalfor
7、mulasorexperimentaldataareusedtopredicttherolldampinginthestripmethods.Toimprovethepredictionofrollmotionsbythesestripmethods,oneoftheauthorscarriedoutaresearchprojecttodeveloparolldampingpredictionmethodwhichhas
