船舶与海洋工程毕业设计外文翻译

·毕业设计（论文）外文翻译题目7500吨干货船技术设计（总体方案及第三部分）专业船舶与海洋工程班级学生指导教师重庆交通大学2013年ASimplePredictionFormulaofRollDampingofConventionalCargoShipsontheBasisoflkeda'sMethodandItsLimitationYukiKawahara,KazuyaMaekawaandYoshihoIkedaDepartmentofMarineSystemEngineering,OsakaPrefectureUniversity,Sakai599-8531’Japan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.IntroductionIn1970s,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].PreviousPredictionFormulaThesimplepredictionformulaproposedinpreviouspapercannotbeusedformodemshipsthathavehighpositionofcenterofgravityorlongnaturalrollperiodsuchaslargepassengershipswithrelativelyflathullshape.Inordertoinvestigateitslimitation,theauthorscomparedtheresultofthispredictionmethodwithoriginalIkeda’sonewhileoutofitscalculatinglimitation.Fig.1showstheresultofthecomparisonwiththeirmethodofrolldamping.Theupperoneisontheconditionthatthecenterofgravityislowandtheloweroneontheconditionthatthecenterofgravityishigh.Fromthisfigure,therolldampingestimatedbythispredictionformulaisingoodagreementwiththerolldampingcalculatedbytheIkeda’smethodforlowpositionofcenterofgravity,buttheerrormargingrowsforthehighpositionofcenterofgravity.Theresultssuggestthatthepreviouspredictionformulaisnecessarytoberevised.MethodicalSeriesShipsModifiedpredictionformulawillbedevelopedonthebasisofthepredictedresultsbyIkeda’smethodusingthemethodicalseriesships.ThisseriesshipsareconstructedbasedontheTaylorStandardSeriesanditshullshapesaremethodicallychangedbychanginglength,beam,draft,midshipsectionalcoefficientandlongitudinalprismaticcoefficient.Thegeometriesoftheseriesshipsaregivenbythefollowingequations.Proposa