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1、AutomaticFree-FormAll-BrickElementsinMeshesMeshingisanimportantcapabilityintheADINApre-processorthatweareconstantlyworkingtoimprove.Notlongago,wepresentedtheenhancementsmadetoourautomaticfree-formhexdominantmesherandmentionedthatanallbrickmeshcannotbeachievedforageneralbody.InthisNews,wedescribeanin
2、terestingcaseofanimportantclassofproblemswheretheADINAreshercangenerateanall-brickmesh.Whenageometricmodeldoesnothaveedges,itispossibletocreatea100%hexmesh.Often,inbiomedicalengineering,modelscomingfromComputerTomography(CT)orMagneticResonanceImaging(MRI)arestoredintheST1.format(alistoftrianglesdefi
3、ningthesurfaceofthemodel)andtheytypicallydonothavehardedgesduetothewaytheyaregenerated.Whenamodelhasnoedges(typically,abodywithasingleface),therearenotopologicalconstraintsonthehexmesherthatpreventthegenerationofameshconsistingofonlybrickelements.Ofcourse,anautomaticallygeneratedfree-formhexmeshisve
4、rydesirablebecauseforagivenrequiredaccuracyinresults,thenumberofelementsrequired(andhencenodesused)ismuchlessthanwhenusingatetmesh.ThemeshshownbelowwascreatedfromanST1.filedescribingahumantorso(courtesyofAIMSHAPEShapeRepository).Thetopologyofthemodelisonebodymadeupofasinglebodyface(whenloadingtheST1
5、.fileintotheADINAinterface,theridgedetectionanglewassetto180degrees).Themeshdensityfollowsthecurvatureofthemodel.Aboundarylayeriscreatedallaroundthemodelinordertomaximizethequalityoftheelementsontheboundary.Themeshhasabout177,000elementsandtheyareallbricks.Figure1MeshofhumantorsogeneratedfromST1.fil
6、eFigure2DetailofabovemeshshowingthevariationofmeshdensityFigure3Partialcross-sectionshowingtheall-brickmeshinsideBeingabletomeshtheseedgelessmodelswith100%bricksispowerfulnotonlybecausetheelementsareallhexahedrabutalsobecausethemeshescreatedhavefarfewerelementsthantetrahedralmeshesorevenmixedmesheso
7、fthesamedensity,asalreadymentionedabove.ThismethodologyisalsoavailableasanoptionformeshinggeneralADINA-Mbodies(theParasolidbasedADINAModeler),i.e.bodiesestablishedinCADprograms.Note,however,thereisthentheneedtouseafineenoughmeshtomatchthetopologyoftheCADmodel.Hence,greatercareneedstobeexercisedwhenu
8、singthiscapabilitywithADINA-Mbodies.ThisfeatureinADINAofautomaticfree-formmeshingofairbrickelementsisclearlyanimportantcapabilityinmanyareasofthree-dimensionalanalyses.KeyWords:Stereolithography1ST1.format,CT1MRI,CADimport,brickmeshAutomaticHexDominantMeshingFree-formhexdominantmeshinghasbeenavailab
9、leinADINAforseveralyears(sinceversion8.2).However,itisrestrictedtopartswithsomewhatlimitedcomplexityandthemeshsubdivisiononapartmustbeuniform.InADINA8.71thefree-formhexdominantmesherissignificantlyimprovedtohandlemorecomplexpartsandallownon-uniformmeshsubdivision.Inaddition,variousfeaturesthatareava
10、ilableinthefree-formtetmeshercannowbeusedforthehexdominantmesher,e.g.1CUrVatUebaSedrefinement,automaticgrading.Themesherwillalsoautomaticallyrefineareaswhereithasdifficultymeshing.Ideally,onewouldliketogenerateameshwithallhexahedralelements.However,thatisnotpossibleforageneralgeometry.Hence,hexdomin
11、antmeshingisusedinpracticetoobtainmesheswithamixofhexahedra,pyramidsandtetrahedra.Asthenameimplies,themeshertriestogenerateasmanyhexahedraaspossible.Complexmodelsremainchallengingtomeshwithmostlyhexahedrasoitisimportanttoremembertosimplifyasmuchaspossiblethepartspriortoapplyingthehexdominantmeshing.
12、Below,weshowsomemeshesobtainedwiththefree-formhexdominantmesherinADINA8.7.Clickonanimagetoseethedetail.ADINAXXADINAWerecognizethatmeshingisaveryimportantpartofperformingafiniteelementanalysisanditisourgoaltocontinuouslyimprovethemeshingcapabilitiesoftheADINASystem.Keywords:Free-formmesh,hexahedralel
13、ement,brickelement,meshrefinement,automaticmeshgradingEffectiveMeshesusingtheSizeFunctionOptionInmanyproblems,itisveryimportanttobeabletomeshdenselyincertainareasandmorecoarselyinotherareaslikeintheanalysisofthehelmetabove,wherethecontactarearequiresafinemesh.ADINA8.4haspowerfulcapabilitiestoachieve
14、meshgradation,inparticularwhenADlNA-Misused.HerewefeaturethenewSizeFunctionoptionthatgivesgreatflexibilityindefiningmeshdensities.Theoptionisparticularlyusefulwhenthedensitieshavetobeappliedinspecificareasofthemodel.Thereareanumberofsizefunctiontypesavailable: nearapointinspace, nearanaxis(straightl
15、ine), nearaplane, inandnearahexahedronofanyshapez inandnearaboundingbox,and anycombinationoftheabove.Thehexahedronsizefunctiontypeisparticularlyeffectiveforthree-dimensionalcontactproblemswherethecontactareaisexpectedtobeinsideahexahedron.Theanalysisofthehelmetaboveinvolvescontactmodelingandmakesuse
16、ofthehexahedronsizefunction.Thesetupofthemodelisshowninthenextfigure.Theanvil(green)isassumedtohitthehelmetwithinthevolumedefinedbytheyellowhexahedron(sizefunction),andthisiswhereafinermeshisdesired.Thetetrahedralmeshobtainedisthemeshshownatthetopofthiswebpage.Thenextfigureisacloseuptoshowthe(automatic)smoothmeshsizegradationfromveryfinetocoarse.
