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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(automa
17、tic)smoothmeshsizegradationfromveryfinetocoarse.MeshgenerationcapabilitiesinADINAinclude: meshingforIDelementssuchastruss,beam,andpipeelements, 2Dsurfacemeshingforshells,plates,and2Dplanarelements,and general3DmeshingforsolidsandfluidsThissectiononmeshgenerationmostlydescribeour3Dmeshingcapabilities
18、whichinclude: mappedmeshingthatgeneratesbrick,wedge,ortetrahedralelements,and free-formmeshingthatgeneratestetrahedralelements. mixedfree-formmeshingthatgenerateshexahedraalongwithpyramids(ifdesired)andtetrahedraPleaseclickonthelinksbelowfortheexplanationandillustrationofthefeaturesinourmeshgenerati
19、oncapabilities.AnisotropicTriangularSurfaceMeshingMeshingM.粉QuadSurfaceMeshingAUtOmatiC净Grading_TetrahedralMeshingCurvature-basedMeshing：MappedMeshingMeshAdaptation-RepairSomeotherfeaturesAUtomatiCFree-FormAll-BriCkEIementSinMeSheSAUtomatiCHeXDOminantMeShinqEffeCtiVeMeSheSIISingtheSiZeFUnCtiOrOCtiOn
20、TheBOdVDefeatUreTOOlTheBOdVCleanUDTOOlTheBODYC1.EANUPToolGeometrybodiesoftenhavefaceswithverysmallareascomparedtothemodeldimensions.Ifleftuntouched,theseundesirablebodyfacesleadtothecreationofpoorlyshapedsurfacetrianglesorquadrilaterals.Inturn,theseleadtothecreationofpoorlyshapedthree-dimensionalele
21、ments.TheBODYC1.EANUPtool,whichwillbeavailableinADINA8.3zcanbeusedsimplytoremovebodyedgesandfaceswithdimensionsbelowauser-specifiedlength.Theusercanalsohavemorecontrolbyspecifyingalistofedges/facesnottobemodifiedaswellasalistofedges/facestoberemoved.Afterusingthistooltoremoveundesirableandunnecessar
22、yfaces,anytypeofmeshing(e.g.zmappedmeshing,triangularorquadrilateralfacemeshing,tetrahedralormixedmeshing)canbeperformedonthecleaned-upbody.BelowzweshowtwoexamplesoftheuseoftheBODYC1.EANUPtool.Ineachexample,themodelisshownzandadetailofthemesh.Ifyoumoveyourmouseontooneofthemeshesthatfollow,youwillsee
23、themeshafterthetoolhasbeenapplied.Movingyourmouseawayfromthemeshrestorestheimagewithoutcleanupzsoyoucanseetheareaswherethemeshhasbeenimproved.Example1:OilscreenADINATIME1OOOBodyfacestobecleanedupareshowninblue.Example2:PropellerBodyfacestobecleanedupareshowninblue.TheBODYDEFEATUREToolTheBODYC1.EANUP
24、toolpresentedintheIaStNeWSisusedtoremovesmallfacesandedgesfromthegeometrybodybeforemeshing.Itworksdirectlyonthegeometrybodyandallmeshingoptionscanbeused.Toremovelargerfeatures,includingprotrusionsandholes,whicharenotrelevanttotheanalysis,theBODYDEFEATUREtoolcanbeusedtoobtainamoreeffectivemeshforanal
25、ysis.TheBODYDEFEATUREtool,availableinADINA8.3,worksontheboundarydiscreterepresentation(surfacetriangularmesh)onabody.Typically,thefeaturestoberemovedaregivenasalistoffacesintheinput.Forexample,toremoveacylindricalhole,thetwofacesoftheholearespecified.Theusercanalsospecifyaminimumlengthwhereanysurfac
26、etrianglebelowthelengthwillberemoved,exceptforfaceswhichareidentifiedtobeexcludedfrommodification.Below,weshowthreeexamplesoftheuseoftheBODYDEFEATUREtool.Example1:EngineblockInthefollowingboundarydiscreterepresentation,theholestoberemovedareshowninyellow.Movingyourmouseontothemeshwilldisplaythemesha
27、ftertheBODYDEFEATUREtoolhasbeenapplied.Movingyourmouseawayfromthemeshrestorestheoriginalmesh.ADINABeforedefeaturingZAXTheBODYDEFEATUREtoolisalsousedtoremovetrianglesinthesurfacemeshthatarebelowaspecifiedminimumlength(showninyellowbelow).Ifyoumoveyourmouseontothemesh,youwillseetheeffectoftheBODYDEFEA
28、TUREtool.Example2:KeyboardThemeshplotofakeyboardisshownbelow.Thefeaturestoberemovedarecoloredyellowthearrowkeysandthechannelsurroundingthemanufacturerslabel.Followingisadetailofthemesharoundthearrowkeys.Thefeaturestoberemovedareshowninyellow.IfyoumoveyourmouseontothemeshzyouwillseetheeffectoftheBODY
29、DEFEATUREtool.BeforedefeaturingAdetailofthemesharoundthemanufacturerslabelareaisshownbelow.Thefeaturetoberemoved-thechannelaroundthelabel-isshowninyellow.Asbefore,moveyourmouseontothemeshtoseetheeffectoftheBODYDEFEATUREtoolonthemesh,andmoveitawaytorestoretheoriginalmesh.BeforedefeaturingExample3:ScrewdriverThefeaturestoberemovedareshowninyellow.MoveyourmouseontothemeshtoseetheeffectoftheBODYDEFEATUREtool.TIME100oZx、YAfterdefeaturing
