ansys_to_aqwa

ANSYSTOAQWAMODELTRANSLATOR1.INTRODUCTIONItispossibletouseclassicANSYStocreateanAQWAradiation/diffractionmodel.AnyofthetoolsavailableinWorkbenchorANSYScanbeusedtocreatethemodel.OncethemodeliscreatedanAQWAinputfilecanbewrittenoutusingamacrosuppliedwithANSYS.2.MODELDESCRIPTIONThemodelmustbemeshedwiththemeshthatyouwishtousefortheAQWAanalysis.Ifyouareworkingfromamodelcreatedforastructuralanalysis,itwillprobablybenecessarytore-meshthemodelasthestructuralmeshislikelytobefinerthanisneedforadiffractionanalysis.Thereshouldbealineofnodesatthewaterline,althoughthesenodesdonotneedtocoincidewithnodesonthestructuralmodel.Thetranslationmacrowillonlymakediffractingthoseelementsthatareentirelybelowthewaterline.Iftherearenowaterlinenodestherewillbenodiffractingelementsatthewaterline,whichwillseverelyreducetheaccuracyofthediffractionanalysis.Allthepanelelementsbelowthewatermusthavetheirnormalspointingoutwards.InAQWAtheverticalaxisisalwaystheZ-axis.ThetranslatorcanconvertamodelwitheitherYorZ-axesvertical,buttheX-axismustbehorizontalandpreferablyshouldbealongthefore/aftaxisofthevessel.IfthestructureissymmetricandyouwishtousetheSYMXorSYMYcardsinAQWA,youmustonlyselect½or¼ofthemodelasappropriate.IfyoumodelacompletevesselandspecifyXsymmetry,theAQWAmodelwillcontaintwosetsofcoincidentelements.3.ELEMENTMAPPINGThetranslatormapsSHELL41,PLANE42,SHELL43,SHELL63,SHELL181elementstopanels,andPIPE16,PIPE20,PIPE59elementstoTUBEs.ItdoesnotrecognizeanyotherANSYSelementtypes.AnymaterialorgeometricpropertiescanbeusedfortheshellelementsasAQWAdoesnotneedanypropertiesatallandthetranslatordoesnotusethem.TUBEelementsinAQWAhavematerialdensity,outsidediameter,wallthickness,addedmassanddragcoefficients,soappropriatepropertiesshouldbeusedintheANSYSmodel.PIPE59elementscanhaveaddedmassanddampingcoefficients,andthesewillbetransferred.NotethatANSYSusestheinertiacoefficientCM,whereasAQWAusestheaddedmasscoefficientCA,whereCM=(1+CA).Thiscorrectionismadeautomaticallybythetranslator.4.RUNNINGTHEMACROWhenyouhavecreatedandmeshedamodelasdescribedabove,youcanrunthemacrotogenerateanAQWAinputfile.FirstselecttheelementsthatyouwanttoincludeintheAQWAmodel.Atthecommandlinetype“anstoaqwa”optionallyfollowedbyafilename.TheAQWAinputfilewillbecalled“file.aqwa”,wherefileisthenameofyourdatabaseorthefilenameyouhaveinput.Youwillthenbepromptedtoinputanumberofparametersinawindowasshownbelow.ThetranslatorwillthencreateacompleteAQWA-LINEasciidatafilethatisreadytoruninAQWA.However,readthefollowingsectioncarefully.5.AQWA-LINEDATAFILEThefilewillspecifyrestartstages1-2only.IthasnooptionsexceptREST,soAQWAmayfailifanyoftheelementsarebadlyshaped.ThetotalmassisobtainedbyintegratingoverthewettedsurfaceareaandaddingtheTUBEmasses,soitshouldbereasonablyaccurate.However,theintegrationusedisnotasaccurateasthatinAQWAsotheremaybeasmalldifferencebetweentheweightandbuoyancy,particularlyiftubesrepresentalargeportionofthemodel.ThepositionoftheCGisunknown.Apointmassisplacedatthewater-lineabovetheCB,butyoushouldchangethistothecorrectposition.Themomentsofinertiaareestimatedbasedontheoveralldimensionsofthemodelandusingstandardformulaeforaship.Youshouldchangethesetothecorrectvalues.Themaximumfrequencyiscalculatedfromthemaximumsidelengthoftheunderwaterelements.Therangeoffrequenciesrunsfrom0.1Hztothecalculatedmaximum,instepsof0.1Hz.Thedirectionsareinstepsof15°,overarangethatisdeterminedbythesymmetryyouhavespecified,inaccordancewiththerequirementsofAQWA.