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.162Lecture9ComputationalMesh.163•AnyEFDcalculationisperformedinarectangularparallelepiped-shapedcomputationaldomainwhoseboundariesareorthogonaltotheaxesoftheCartesianGlobalCoordinateSystem.•AcomputationalmeshsplitsthecomputationaldomainintorectangularparallelepipedsnamedcellsbyasetofplanesorthogonaltotheCartesianGlobalCoordinateSystem'saxes.•Fluidcells–thecellsthatareentirelyinthefluidregion.•Solidcells–thecellsthatareentirelyinthesolidregion.•Partialcells–thecellsthatarepartlyinsolidandpartlyinfluid.•Irregularcells–thepartialcellsinsidewhichthenormaltothesolidsurfacecannotbedeterminedComputationalCells.164PartialcellPartialcellFluidcellSolidcellZerolevelcell(basiccell)FirstlevelcellTypesofComputationalCells.1651.Constructingthebasicmeshforaspecifiednumberofcellsandstretchingorcontractingthebasicmeshlocallytobetterresolvethemodelandflowfeaturesbytheuseofcontrolplanes.2.Splittingthebasicmeshcellseithertocapturethesmallsolidfeatures,orresolvethesubstanceinterface(fluid/solid,fluid/porous,porous/solidinterfacesorboundarybetweendifferentsolids)curvature(e.g.,small-radiuscirclesurfaces,etc.)–i.e.smallsolidfeaturesrefinement,curvaturerefinementandtolerancerefinement.3.Refiningthemeshcellsofaspecifictype(refinementofeitherallcells,orfluid,and/orsolidcells,and/orpartialcells).4.Refiningtheobtainedmeshtobetterresolvenarrowchannels–i.e.narrowchannelrefinement•Perfectmeshingcanbeanart,goodmeshingisdonebythesoftware.•Badmesh-badresults.•Toomuchmesh–longcalculationMeshConstructingStages.166LocalinitialmeshsettingsInitialmeshingsettingsInitialMeshandLocalInitialMeshDomainbasedGeometrybased.167•LevelofinitialmeshgovernsthenumberofBasicMeshcellsandthedefaultprocedureofmeshrefininginthemodel’snarrowchannels.•Manualspecificationoftheminimumgapsize,whichinfluenceresolvingofthemodel’snarrowchannelsbytheinitialmesh.•Manualspecificationoftheminimumwallthickness,whichinfluencerefinementofthemeshwithinthemodel'swalls.•Optimizethinwallsresolution:keepitactivated..168•Thebasicmeshisameshofzerolevelcells.Incaseof2Dcalculationonlyonebasicmeshcellisgenerated(automatically)alongtheeliminateddirection.•BydefaultEFDconstructseachcellasneartoacubicshapeaspossible.•SometimesitisnecessarytomodifythedefaultnumberofcellsinX,YorZmanuallyBasicMesh.169•Theinitialmeshisfullydefinedbythegeneratedbasicmeshandtherefinementsettings.•Eachrefinementhasitscriterionvalueandlevel.–Therefinementcriterionvaluedenoteswhichcellshavetobesplit–Therefinementleveldenotesthesmallestsizetowhichthecellscanbesplit.–Thedifferenceinrefinementlevelforneighboringcellscannotbemorethan1•Regardlessoftherefinementconsidered,thesmallestcellsizeisalwaysdefinedwithrespecttothebasicmeshcellsizesotheconstructedbasicmeshisofgreatimportancefortheresultingcomputationalmesh.InitialMesh0123.170ResolvingtheInterfaceBetweenSubstances•Smallsolidfeaturesrefinement•Curvaturerefinement•Tolerancerefinement.171Smallsolidfeaturesrefinementlevel=1.Smallsolidfeaturesrefinementlevel=4.EFDhasdetectedthehorizontalnarrowcylinderbutthelevelisnotenoughtocapturethecylinder.Thehorizontalcylinderisresolved.Notethatthemeshisonlyrefinedintheareaofthecylinder.SmallSolidFeaturesRefinement.172Solid/FluidInterfaceCurvaturecriterion(anglebetweennormals)=0.318radCurvaturerefinementlevel=0Nosplitcells.Curvaturerefinementlevel=1Thepartialcellsweresplitonce.CurvatureRefinement.173ToleranceRefinement•ToleranceRefinement–Specifyhowwellthemeshpolygonsresolvethesurface–Givesmorecontrolforrefiningbasedonsolidsize•RefinementLevel–Setshowmanytimesacellcansplittomeetcriterion•Criterion–Controlsprecisionofthepolygon-surfacerepresentation–Cellwillbesplitif‘h’isgreaterthanthetolerancecriterion.174•UsingtheRefiningCellstabyoucanrefinecellsofaspecifictype.–Refineallcells–Refinefluidcell–Refinesolidcells–Refinepartialcells•SpecifythecorrespondinglevelofrefiningcellswithrespecttotheBasicMesh.–N=0…7–sizewillbein2Ntimesineachdirection,or8Ntimesbyvolume,smallerthanthebasicmesh’scellssize.RefiningCellsbyType.175•UsingtheNarrowchannelstabyoucanspecifyanadditionalmeshrefinementinthemodel’sflowpassagesinordertoobtainamoreaccuratesolution.•Bydefaultmeshrefinementinnarrowchannelsisperformedalways.NarrowChannelRefinement.176.177•Contractand/orstretchthebasicmeshinthespecifieddirectionsandregionsbyspecifyingthepositionofsomebasicmeshplanes,namedControlPlanes,andthemeshstep,i.e.distancebetweenneighboringmeshplanes.•Controlplanescanbeselectedfromexistinggeometryfacesorbycoordinates,bothmodifyablebysliderbar.SpecifyingControlPlanes.178SpecifyingLocalInitialMesh•TheLocalInitialMeshdialogboxallowsustospecifyaninitialmeshinalocalregionofthecomputationaldomaintobetterresolvethemodelspecificgeometryand/orflow(and/orheattransferinsolids)peculiaritiesinthisregion•Thelocalregioncanbedefinedbyacomponent,face,edgeorvertex.•Youcanspecifythelocalinitialmeshnearlyinthesamemannerastheglobalinitialmesh–thesmallsolidfeatures–theinterface’scurvature–themeshinnarrowchannels–Theonlyexceptionisthatthebasicmeshisnotspecifiedinalocalregion(itistakenfromtheglobalini