用Ideas对大模型划分网格.docx
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用Ideas对大模型划分网格.docx
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用Ideas对大模型划分网格
LargeModelFreeMeshingMethodsinI-DEAS10
Thisdocumentisbaseduponexperiencewithmeshingverylargeautomotivecomponentmodels.Componentsontheorderof10,000surfacesaretypicalofthisenvironment.Theintentistogeneratesolidfreemeshesonthesecomponentsinthemostefficientmannerpossible.
Largemodelfreemeshingreliesheavilyonsectionmeshingtools.Beforedefiningthelargemodelfreemeshingprocess,itisimportanttoreiteratethegoalsofsectionmeshing.
1.Eachsectionismeshable
2.ThesectionsaredefinedsuchthatunnecessaryCADdetailsareremovedtoreducetotalelementcountinthefiniteelementmodel
3.Unstitchedgeometryisrepairedwithsectionssothatthesectionsdefineawatertightvolume
4.CertaintopologyfeaturesnotintheCAD,butimportanttotheanalysis,arerepresentedbysections
ReviewCADTopology
PriortobeginningsectioncreationkeyelementsoftheCADmodelmustbeunderstood.DoestheCADmodelcontainunwantedfreeedgesorunstitchedconditions?
Ifunwantedfreeedgesexist,whatisthetypicaldistancebetweenadjacentfreeedges?
Whatisthelengthoftheshortestedgeandhowprevalentareshortedges?
Arethereuntrimmedsurfacesorsurfacesthataremissing?
WhatfeaturesintheCADcanbeneglectedtoreducefiniteelementcountandwhatfeaturesintheCADarecriticaltotheanalyst?
TypicallytheCADdatacontainsnearlyfullystitchedvolumes.Italsousuallyhasveryshortedgesontheorderof0.01mm.Missingsurfacesmayneedtoberecreated,butifthemissingsurfaceissmall(1-4timesglobalelementlength),thentheareacanbestitchedupwithsectioncommandsratherthanwithsurfacecreation.Assumingtheaboveistrue,thenthefollowingsectioncreationguidelineswillworkwell.
CADAbstraction
SectionmeshingisusedtoabstracttheCADintotopologysuitableformeshing.Thesectiontopologywill:
1.Mergesmallsurfaceswithneighboringsurfacesasacollectionofsurfacesbeingonesection
2.Representfreeedgesasstitchedsectioncurves
3.Eliminatesmalledgesasacollectionofedgesbeingonesectioncurve
Automaticandmanualtoolsareusedtogeneratesectionssuitableformeshing.
AutoCreateSections
Forthetypicalautomotivepowertrainparts,thefollowingAutoCreateSectionsettingsareuseful:
1.SectionOptions(MB3)
a.Gapsize:
0.01mm
b.Defaultsforallothers
2.Curvaturelimit:
60degrees
3.
Advancedoptions:
pre-processfillets:
YES
a.Filletminimumradius:
0.0
b.Filletmaximumradius:
4*(globalelementlength)/π
4.Advancedoptions:
combinecylindricalsurfaces:
YES
a.Mergesurfacesbasedontargetelementlength:
YES
b.Targetelementsizeequalsglobalelementlength
5.Selectallsurfaces
AutoCreateSectionswilloutputnotbeperfect.Cleanupoperationswillberequiredtofurtherremoveconditionsthatcreatepoortrianglemeshquality.Examplesinclude:
1.Sectionfreecurves
2.Nearlycoincidentcurves(parallelandoffsetbyashortdistance)
3.Shortcurves(lessthan10%desiredelementlength)
4.Unmeshablesections
Amixtureofautomaticandmanualtoolsareusedduringthemeshingprocesstocorrecterrorsinsectiontopology.
SectionFreeCurves
AutoCreateSectionswillfullydefinesectionsontheCAD.Thesesectionsmayormaynotbestitched.Ifunstitched,thensectionfreecurveswillexist.Sectionfreecurvesneedtoberemovedforsolidmeshgeneration.Stitchingsectionfreecurvestogetherassuresthatthetrianglemeshesusedtogeneratesolidsarestitchedtooneanother.Thefollowingtoolsareprovidedtoidentifysectionfreecurves:
1.SectionFreeCurves(undertheSectionQualityCheckstack)
2.ModelCheckOptions,sections,freecurves
TheSectionFreeCurvescheckproducesatemporarygraphicaldisplayofsectionfreecurves.Thefreecurvesarehighlighted,butthegraphicsareremovedafterthefirstredisplayofthemodel.
ModelCheckprovidesawaytopermanentlydisplayFEMqualityinformationviagraphicalrepresentationsonthemodel.Inthiscase,sectionfreecurvesarepermanentlyhighlightedaslongasModelCheckisturnedON.
SectionfreecurvesarestitchedwiththeReplaceCurvecommand.Thiscommandwillreplacethefirstcurveselectedwiththesecondcurveselected.Essentiallythisisamergingof“coincident”curves.
Obtainacompletelystitchedsectionmodel,andthenbeginmeshingsectionsbasedongroupsautomaticallygeneratedduringAutoCreateSections.
GeneratingTriangleMeshesonSections
Inpreviousreleasesitwasrecommendedtonotmeshanysectionsuntilallsectioneditingwascompleted.PerformanceenhancementstoI-DEAS10removethatobstaclesothatmeshingmayproceedimmediatelyfollowingsectioncreation.Meshingthesectionsfirstletselementqualitydictatewheresectionsneedtobefixed.Thatmeansthatnoteveryshortcurveornarrowregionneedstobecorrected.Onlysectionsthatcauselowqualityelementsneedtobefixed.Focusingonelementqualityratherthansectionqualityimprovestheoverallmeshingprocesstime.
MeshingtheFillets
Whenpre-processingfilletsduringAutoCreateSections,thesoftwareincludesinagroupallofthesectionsitthinksaredefinedonfillets.Thisgroupisnamed“FILLETSECTIONS”.Definemeshesonallofthesesectionsatonce:
1.Globalelementlengthtypicallyfrom5to10mm
2.Elementtype:
lineartriangle
3.Freeoptions:
freemappedON
Eventhoughtheintentistogenerateaparabolictetrahedronmesh,wegeneratemesheswithlinearelements.Oneofthefinalstepswillbetoconvertthetetrahedronmeshtoparabolic.TurningONthefreemappedoptionwillresultinmapped-likemeshesonsectionsthatareofa4-sidednature.Inthecaseoffillets,freemappedcanproduceaverystructuredmeshsincefilletsectionsareoften4-sidedwithtwoparallellongsidesand2shortsides.
GeneratethemeshonalloftheFILLETSECTIONS.Itispossiblethatnotallsectionswillmesh.Usuallymeshingwillfailduetomaximumareaplanelimitations.Theunmeshablesectionswillbeaddedtothepre-selectlist.Createagroupoutofthepre-selectedsections.Ifonlyahandfulofsectionsareunmeshable,youmaywanttoeditthemmanuallysothattheyaremeshable.Ifmanysectionsareunmeshable,thenconsiderdoingthefollowing:
1.Displayunmeshablesectionsgroup
2.Addtothegroupsurfacesrelatedtosectionsingroup(useQuickFiltersintheManageGroupsform)
3.Deleteallsectionsinthegroup
4.
Createsinglesurfacesectionsonallsurfacesinthegroup
CreatingsinglesurfacesectionsonagroupofsurfacesisachievedwiththeSingleSectionCreatecommand.Byconvertingunmeshablesectionsintosinglesurfacesections,yougreatlyincreasetheprobabilitythatthesectionswillmeshsinceparameterspacecanbeusedtomeshthesection.Usuallyonlyverylargeglobalelementsizes(comparedtothesurface/sectionsize)willcauseasinglesurfacesectiontofailtomesh.
5.Generatemeshesonallofthesectionsdefinedin4
Again,someofthesectionsmaystillfailtomeshduetoexcessiveelementsize.AnewfeatureofI-DEAS10istheabilitytoremeshshellmesheswithoutfirstdeletingthem.TotrytomeshsectionsfailinginStep5,
6.
SelecttheModifyMeshPreviewicon
7.TurnONMB3AddAdjacent
8.SelectsectionsfailingtomeshinStep5
9.Modifytheglobalelementlengthofthefailingsectionstosomethingsmaller(maybehalftheoriginallength)
ThemesherwillproducenewelementdistributionsalongtheboundariesoftheselectedsectionsinStep9,eventhoughsomeofthoseboundariesmaybefrozenwithanexistingmesh.
10.PreviewthemeshandOKoutoftheModifyMeshPreviewform
Manytimesreducingtheelementsizeinthismannerwillleadtoacompletelymeshedsetofsections.AssumingthattheFILLETSECTIONSarenowmeshed,thenexttaskistomeshthecombinedcylindricalsurfacesections.ItisOKtohaveunmeshedsectionsatthispoint.Optionallyyoumaywishtofixallunmeshedsectionsasalaststeptothesectionmeshingtask.Infactsomeoftheunmeshedsectionsmayinadvertentlygetfixedduringthesectioneditingtask.
MeshingtheStackedCylinderSections
AutoCreateSectionsalsocreatedagroupofsectionsnamed“STACKEDSECTIONS”.Thesesectionsarecomposedofneighboringcylindricalsurfacesthathavebeencombinedintoasinglesection.ThesesectionsmaycontainO-ringgrooves,fillets,chamfers,andcylindricalfacesthatdefineacylindricalfeaturesuchasascrewtap.Definemeshesonthesesectionsatonce:
1.Globalelementlengthtypically5to10mm
2.Elementtype:
lineartriangle
GeneratethemeshesontheSTACKEDSECTIONSatonce.Again,someofthesectionsmaynotmesh,buttheywillbeaddedtothepre-selectlist.Storethefailingsectionsinagroupandcorrectmeshabilityproblemsusingthemethodsdescribedpreviously.
MeshingtheRemainingSections
AutoCreateSectionscreatedagroupofsectionsnamed“STANDARDSECTIONS”aswell.DefinemeshesonthesesectionsinthesamemanneraswasdonefortheSTACKEDSECTIONS.Completethemeshingtaskforthesesectionswiththemethodsalreadydescribedfortheothersectiongroups.
MeshQuality:
ElementStretch
Stretchedtriangleswillproduceverypoorsolidelements.Thisprocessidentifiesalltriangleswithstretchlessthan0.1.Astretchvalueof1.0indicatesawell-formedelement,whileastretchof0.0indicatesacollapsedelement.Asthesurfacetrianglestretchvaluesincrease,sodoestheprobabilityofgeneratingaqualitysolidmeshthatwillsuccessfullysolve(forexampleinNastranlinearstatics).Performthefollowingtaskstoidentifypoormeshareas:
1.SelecttheQualityChecksiconandselectallelements
2.Ch
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