gambit-23-Lecture-06a--VolumeMeshing

VolumeMeshingApproachAhigh-qualityhexmeshisgenerallypreferredoveratetmesh.Reduceddiscretizationerrorandfalsenumericaldiffusionforagivenmeshsize.SignificantlylowercellcountExample:Comparethecellcountfora10×10×10cubeusinghexandtetwithacellsizeof1.Hexmeshgenerates1,000cells.Tetmeshgenerates7,726cells!Forahexmesh,geometriestypicallyneedtobedecomposedintosimpleronessothatoneofthehexmeshingschemescanbeused.Insomecases,thegeometrycanbeverycomplex.Hexmeshingcanbeexpensiveorimpractical.Inthesecases,atetorhybridmeshispreferredinordertoreducemeshingeffort.VolumeMeshingUponpickingavolumeGAMBITwillautomaticallychooseatypebasedonthesolverselectedandthecombinationofthefaceTypesofthevolume.Inambiguouscases,GAMBITchoosestheTet/Hybrid:TGridcombinationAvailableelement/schemetypecombinationsHexMap,Submap,TetPrimitive,Cooper,StairstepHex/WedgeCooperTet/HybridTGrid,HexCoreVolumeMeshes-HexExamplesHex–MapHex--SubmapHex–TetPrimitiveHex–CooperHex/WedgeandTet/HybridExamplesHex/Wedge:CooperTet/Hybrid:TGridTet/Hybrid:HexCoreHexMeshing–MapAmappablevolume:IsalogicalcubeHasallfaceseithermappableorsubmappableHastopologicallymatchingmeshonallfaces.MeshMeshsubmapfaceHexMeshing–SubmapAsubmappablevolume:Hasallfaceseithermappableorsubmappable.Hastopologicallymatchingoppositefaces.MeshMeshHexMeshing–TetPrimitiveTet-PrimitiveschemeAllhexelementsinafour-sided(tetrahedral)volumeVolumesdirectlymeshableusingTetPrimitiveschemeHowthetetprimitiveschemeworksConnectcenterpointsonedges,facesandthevolumeMeshthefoursubvolumesusingthemapscheme.MeshHexMeshing–CooperTheCooperschemeprojectsorextrudesafacemesh(orasetoffacemeshes)fromoneendofavolumetotheotherandthendividesuptheextrudedmeshtoformthevolumemesh.TheprojectiondirectionisreferredtoastheCooperdirection.Facestopologicallyperpendiculartothisdirectionarecalledsourcefaces.Sourcefacesneednotbepremeshed.Atleastonesourcefacemustnotbemeshedandmustspantheentirecrosssection.Facesthatintersectthesourcefacesarereferredtoassidefaces.SidefacesmustbeeithermappableorsubmappableSideFaces(twohidden)CooperdirectionSourceFacesCooperExamplesVolumeContainingMultipleHolessourcefacessourcefacessourcefacesSourceFacesNotParallelsourcefacesMultipleSourceFacesandMultipleInteriorLoopsCooperToolMethodologyWhentheCooperschemeisselected,asourcefacelistboxappearsinthepanel.IfGAMBITchoosesthesourcesfacesCheckthesourcefacelistandverifythatGAMBIThaschosenthecorrectfaces.Ifnecessary,changethesourcefacesselection.GAMBITmaynotbeabletoresolvethesourcefacesManuallyselectthesourcefacesIfnecessary,manuallychangethevertextypes(discussedinlecture3)onsomeofthesidefacesTroubleshootingtheCooperToolABCProblem:SourcefacesA,B,andCarepremeshed.TheCoopertoolfails.Why?Howcanthisvolumebemeshed?TroubleshootingtheCooperToolSolution:ThemeshonsourcefacesAandBcannotbeprojectedontofaceC(thesourcefacesareoverconstrained.DeletethemeshonfaceCinordertogeneratethevolumemesh.ABCTroubleshootingtheCooperToolProblem:Abrickissplitasshown.TheCoopertoolfails.Why?Whatcanbedonetogenerateavolumemesh?ABCTroubleshootingtheCooperToolSolution:Coopertoolfailsbecausenologicalaxisexists.IffacesAandBaresourcefaces,thenfaceCmustbeeithermappableorsubmapple.FaceCcontainsavoidandcanonlybepaved.Splitthevolumewithafaceasshown.UseFaceA1asonesourcefaceforvolume1andusefaceC2asonesourcefaceforVolume2.A1Volume1Volume2C1ABCTroubleshootingtheCooperToolProblem:TheCoopertoolfailsbecausetheinteriorloopsonsourcefacesAandBeitheroverlaporareclose.ABInteriorloopsTroubleshootingtheCooperToolABInteriorloopsA1A2Solution:SplitsourcefaceAasshown.NeitherfaceA1norA2containclosedinteriorloops.Example:manuallychangethevertextypes3SourceFacesHowtoMakeaVolumeCooperableThreeoptionstousetheCooperTool:Manuallychangevertextypesonthesidefacestomakethemmappableorsubmappable.Manuallyselectthesourcefaces.GAMBITwillattempttomakesidefacesmappableorsubmappable.Enforcethemaporsubmapschemeonthesidefaces.SESECCEEEEEETet/HybridMeshingTetrahedral/HybridMeshScheme-TGridMostvolumescanbemeshedwithoutdecomposition,regardlessofcomplexity.Useboundarylayerstocreatehybridgrids(prismlayersonboundariestocaptureimportantviscouseffects).Useonvolumesthatareadjacenttovolumesthathavebeenmeshedwithhexelementswillautomaticallyresultinatransitionlayerofpyramids.1HexCooper2Tet:TGridPyramidlayer3Hex/WedgeCooperTet/HybridMeshing–TroubleshootingQualityofthetetrahedralmeshishighlydependentonthequalityofthetriangularmeshontheboundaries.Initializationprocessmayfailorhighlyskewedtetrahedralcellsmayresultifthereexists:highlyskewedtrianglesontheboundaries.largecellsizevariationbetweenadjacentboundarytriangles.smallgapsthatarenotproperlyresolvedwithappropriatelysizedtriangularmesh.Difficultiesmayariseingeneratinghybridmesh.Cannotgrowpyramidsfromhighaspect-ratiofaces.Prismandpyramidgenerationmaynotworkproperlybetweensurfacesformingverysmallangles.Low-qualitypyramidPrismlayersmallangleHexCoreMeshingCombinesTet/HybridmeshwithCartesianmeshinthecore.Fewercellswithfullautomationandgeometricflexibility.ImportantHexCoredefaults:Hexcore_Offset_LayersThenumberofoffsetlayers(celllayersbetweenwallandhexahedralcore);defaultvalueis3.Hexcore_Quad_Surface_SplitControlsquad/trisplittingandeliminatespyramidcellswhenturnedon;seeAppendixHexcore_MethodControlsthemethodusedtocreateHexCore–StandardorTGridHexCore.TGridHexCorerequiresspecificationofbufferlayers.HexCoreMeshingFlowVolumeInsideanAutomobileManifoldFlowVolumeAroundaBoatHullAssigningBoundaryandContinuumTypesBoundaryTypeFormEnterentitiestobegroupedintosinglezoneinentitylistbox.Firstchooseentitytypeasfaceoredge.Selectboundarytypeforzone(entitygroup).AvailabletypesdependonSolverNamezoneifdesired.Applydefineszoneandboundarytype.Canalsomodifyanddeletezone/boundary.Bydefault,Externalfaces/edgesarewallsInternalfaces/edgesareinteriorContinuumTypeformContinuumtypesaredefinedinasimilarwayasboundarytypes.Multiplefluid/solidzonescanbedefined.Unspecifiedcontinuumzonesarealwaysassignedthefluidtype.Example:FlowoveraHeatedObstacleBoundaryName=outletType=PRESSURE_OUTLETContinuumName=obstacleType=SOLIDBoundaryName=inletType=VELOCITY_INLETDefaults:Example:FlowoveraHeatedObstacleBydefault,the4remainingexternalfaceshavetheNameandType:Boundary:Name=wallType=WALLBydefault,theoneremainingvolumehastheNameandTypeContinuum:Name=fluidType=FLUIDAppendixMeshedSizeFunctionfromBoundaryLayerCapMeshedSizeFunctionstartingfromboundarylayercapimprovessizetransitionbetweentheboundarylayerandvolumemesh.Usefulforexternalaerodynamicsapplications.SpecifytheGrowthRateandMax.Sizeforthemeshgrowingfromthelastprismlayerintothevolume.Example:3Dwingprofilewith12boundarylayers;themeshedsizefunctionisusedforsmoothtransitiontothetetvolumemesh.Hex-CoreMeshing–SurfaceSplitOptions1(default)Splitboundaryquadinto2triangleshangingedgescreated(NOTallowedinFIDAP)Smoothboundaryhexeswithlargerhexcore0BoundaryquadsareNOTsplitPyramid(transition)elementscreatedBoundaryhexesnotsmoothedGeometry:CylinderEditDefault:Mesh.Cartesian.Hexcore_Quad_Surface_SplitFIDAP8Example:FlowoveraHeatedObstacleBoundary:Name=outletType=PLOTBoundary:Name=outletType=PLOTContinuum:Name=stepType=SOLIDLinear/QuadraticElements(FIDAP/POLYFLOWUSERSONLY)GeneraltoolsHigher-orderelementsForFEMcodes(FIDAPandPOLYFLOW),theelementordercanbechangedatallthreemeshinglevelsOnlylinearandquadraticelementsaredirectlyavailableAchangetoquadraticelementtypeatonelevelwillautomaticallychangetheelementtypeinotherlevelsThefollowingtablepresentsthemostcommonlyusedandrecommendedquadraticelementtypesforFEMsolversPOLYFLOWFIDAPEdge3-node3-nodeFace8-nodequad9-nodequadVolume21-nodebrick27-nodebrick演讲完毕，谢谢观看！