ADINA Mesh Generation 网格划分 仿真软件.docx

AutomaticFree-FormAll-BrickElementsinMeshesMeshingisanimportantcapabilityintheADINApre-processorthatweareconstantlyworkingtoimprove.Notlongago,wepresentedtheenhancementsmadetoourautomaticfree-formhexdominantmesherandmentionedthatanallbrickmeshcannotbeachievedforageneralbody.InthisNews,wedescribeaninterestingcaseofanimportantclassofproblemswheretheADINAreshercangenerateanall-brickmesh.Whenageometricmodeldoesnothaveedges,itispossibletocreatea100%hexmesh.Often,inbiomedicalengineering,modelscomingfromComputerTomography(CT)orMagneticResonanceImaging(MRI)arestoredintheST1.format(alistoftrianglesdefiningthesurfaceofthemodel)andtheytypicallydonothave"hard"edgesduetothewaytheyaregenerated.Whenamodelhasnoedges(typically,abodywithasingleface),therearenotopologicalconstraintsonthehexmesherthatpreventthegenerationofameshconsistingofonlybrickelements.Ofcourse,anautomaticallygeneratedfree-formhexmeshisverydesirablebecauseforagivenrequiredaccuracyinresults,thenumberofelementsrequired(andhencenodesused)ismuchlessthanwhenusingatetmesh.ThemeshshownbelowwascreatedfromanST1.filedescribingahumantorso(courtesyofAIMSHAPEShapeRepository).Thetopologyofthemodelisonebodymadeupofasinglebodyface(whenloadingtheST1.fileintotheADINAinterface,theridgedetectionanglewassetto180degrees).Themeshdensityfollowsthecurvatureofthemodel.A"boundarylayer"iscreatedallaroundthemodelinordertomaximizethequalityoftheelementsontheboundary.Themeshhasabout177,000elementsandtheyareallbricks.Figure1MeshofhumantorsogeneratedfromST1.fileFigure2DetailofabovemeshshowingthevariationofmeshdensityFigure3Partialcross-sectionshowingtheall-brickmeshinsideBeingabletomeshthese"edgeless"modelswith100%bricksispowerfulnotonlybecausetheelementsareallhexahedrabutalsobecausethemeshescreatedhavefarfewerelementsthantetrahedralmeshesorevenmixedmeshesofthesamedensity,asalreadymentionedabove.ThismethodologyisalsoavailableasanoptionformeshinggeneralADINA-Mbodies(theParasolidbasedADINAModeler),i.e.bodiesestablishedinCADprograms.Note,however,thereisthentheneedtouseafineenoughmeshtomatchthetopologyoftheCADmodel.Hence,greatercareneedstobeexercisedwhenusingthiscapabilitywithADINA-Mbodies.ThisfeatureinADINAofautomaticfree-formmeshingofairbrickelementsisclearlyanimportantcapabilityinmanyareasofthree-dimensionalanalyses.KeyWords:Stereolithography1ST1.format,CT1MRI,CADimport,brickmeshAutomaticHexDominantMeshingFree-formhexdominantmeshinghasbeenavailableinADINAforseveralyears(sinceversion8.2).However,itisrestrictedtopartswithsomewhatlimitedcomplexityandthemeshsubdivisiononapartmustbeuniform.InADINA8.71thefree-formhexdominantmesherissignificantlyimprovedtohandlemorecomplexpartsandallownon-uniformmeshsubdivision.Inaddition,variousfeaturesthatareavailableinthefree-formtetmeshercannowbeusedforthehexdominantmesher,e.g.1CUrVatUebaSedrefinement,automaticgrading.Themesherwillalsoautomaticallyrefineareaswhereithasdifficultymeshing.Ideally,onewouldliketogenerateameshwithallhexahedralelements.However,thatisnotpossibleforageneralgeometry.Hence,hexdominantmeshingisusedinpracticetoobtainmesheswithamixofhexahedra,pyramidsandtetrahedra.Asthenameimplies,themeshertriestogenerateasmanyhexahedraaspossible.Complexmodelsremainchallengingtomeshwithmostlyhexahedrasoitisimportanttoremembertosimplifyasmuchaspossiblethepartspriortoapplyingthehexdominantmeshing.Below,weshowsomemeshesobtainedwiththefree-formhexdominantmesherinADINA8.7.Clickonanimagetoseethedetail.ADINAXXADINAWerecognizethatmeshingisaveryimportantpartofperformingafiniteelementanalysisanditisourgoaltocontinuouslyimprovethemeshingcapabilitiesoftheADINASystem.Keywords:Free-formmesh,hexahedralelement,brickelement,meshrefinement,automaticmeshgradingEffectiveMeshesusingtheSizeFunctionOptionInmanyproblems,itisveryimportanttobeabletomeshdenselyincertainareasandmorecoarselyinotherareaslikeintheanalysisofthehelmetabove,wherethecontactarearequiresafinemesh.ADINA8.4haspowerfulcapabilitiestoachievemeshgradation,inparticularwhenADlNA-Misused.HerewefeaturethenewSizeFunctionoptionthatgivesgreatflexibilityindefiningmeshdensities.Theoptionisparticularlyusefulwhenthedensitieshavetobeappliedinspecificareasofthemodel.Thereareanumberofsizefunctiontypesavailable: nearapointinspace, nearanaxis(straightline), nearaplane, inandnearahexahedronofanyshapez inandnearaboundingbox,and anycombinationoftheabove.Thehexahedronsizefunctiontypeisparticularlyeffectiveforthree-dimensionalcontactproblemswherethecontactareaisexpectedtobeinsideahexahedron.Theanalysisofthehelmetaboveinvolvescontactmodelingandmakesuseofthehexahedronsizefunction.Thesetupofthemodelisshowninthenextfigure.Theanvil(green)isassumedtohitthehelmetwithinthevolumedefinedbytheyellowhexahedron(sizefunction),andthisiswhereafinermeshisdesired.Thetetrahedralmeshobtainedisthemeshshownatthetopofthiswebpage.Thenextfigureisacloseuptoshowthe(automatic)smoothmeshsizegradationfromveryfinetocoarse.