-Introduction To Meshing Introduction ToMeshing

1 - Introduction To Meshing IntroductionIntroductionIntroductionIntr oductionThischapterincludesmaterialfromt hebook PracticalFinitThischapterincludesmateria lfromthebook PracticalFinitadditional material added by Gareth material added by Gareth : Tata Johnson Controls Courtesy: Tata Johnson Controls WhyDoWeCarryOut Meshing ?WhyDoWeCarryOut Meshing ?No. of Points = No. of Points = DOF per Point = 6 DOF per Point = 6 Total equations = hebasicideaofFEAistomakecalculationsaton lylimited(FinihebasicideaofFEAistomakeca lculationsatonlylimited(Finientiredomain (surfaceorvolume).Anycontinuousobjecthas entiredomain(surfaceorvolume). or Meshing (nodes and elements).discretization or Meshing (nodes and elements).11 Meshing -ToMeshingToMeshingToMeshingToMeshingFin iteElementAnalysis .Italsohasbeenreviewedandhas FiniteElementAnalysis .Italsohasbeenreviewedandhas ols Automotive Limited, Indiaols Automotive Limited, IndiaNo.))

2 Of Nodes = 8 No. of Nodes = 8 DOF per Node = 6 DOF per Node = 6 Total equations = 48 Total equations = 48(Finite)numberofpointsandtheninterpola tetheresultsforthe(Finite)numberofpoints andtheninterpolatetheresultsforthehasinf initedegreesoffreedomandit sjustnotpossibletosolvehasinfinitedegree soffreedomandit sjustnotpossibletosolvereducesthedegrees offreedomfrominfinitetofinitewiththehelp ofreducesthedegreesoffreedomfrominfinite tofinitewiththehelpof- Introduction To Meshing TypesOf ElementsTypesOf ElementsTypesOf ElementsElementsElements1D2D1D2 DMidsurfaceMidsurfaceyxtxzt -thickness of platett/2t -thickness of platet/2x >>> y, zx , z >>> yx >>> y, zOne of the dimensions is x , z >>> yTwo of the dimensions are One of the dimensions is very large in comparison to Two of the dimensions are very large in comparison to very large in comparison to the other twovery large in comparison to the third onethe other twoElement shape line Additional data from user-the third oneElement shape quad.

3 Tria Additional data from user Element shape line Additional data from user-remaining two dimensionsAdditional data from user -remaining dimension remaining two area of cross section -remaining dimension area of cross section Element type rod, bar, thicknessElement type thin shell, Element type rod, bar, beam, pipe, axisymmetric Element type thin shell, plate, membrane, plane beam, pipe, axisymmetric shell, etcPracticalapplications-Longplate, membrane, plane stress, plane strain, , axi-symmetric solid, etc. shell, etcPracticalapplications-Longshafts,beam s,pinjoint,con-symmetric solid, etc. Practical applicationsshafts,beams,pinjoint,con-ne ctionelements, applications-Sheetmetalparts,plasticnect ionelements, ,plasticcomponentslikeaninstru-component slikeaninstru-mentpanel, , ToDecideTheElementTypeHow ToDecideTheElementTypeHow ToDecideTheElementTypeElement type Element type Geometry size and shapeType of analysisGeometry size and shapeType of analysisA.

4 GeometrySizeAndShapeA. GeometrySizeAndShapeForananalysis, , (by Meshing using nodes and elements).completely (by Meshing using nodes and elements).Thegeometrycanbecategorizedas1 D,2D,or3 DbasedontheThegeometrycanbecategorizedas 1D,2D, : Used for geometries havingone of the dimensions that 1 DElement: Used for geometries havingone of the dimensions that , ,theareainputdataandassignedtotherespect iveelementsinputdataandassignedtotheresp ectiveelementsPracticalexample:Longshaft ,rod,beam,column,spotwelding,bolPractica lexample:Longshaft,rod,beam,column,spotw elding,bol22 Meshing -ElementsElements3 DOther3 DOtherx ~ y ~ zx ~ y ~ zAll dimensions are com-Mass Point element, con-All dimensions are com-parableMass Point element, con-centrated mass at the center parableElement shape tetra, centrated mass at the center of gravity of the Element shape tetra, penta, hex, pyramid Additional data from user of gravity of the component Spring translational and rotational Additional data from user nonetranslational and rotational stiffness noneElement type solid stiffnessDamper-damping coef-Element type solid Practical applications Damper-damping coef-ficientPractical applications -Transmission casing, ficientGap Gap distance, -Transmission casing, engine block, crankshaft, Gap distance, stiff-ness, frictionRigid RBE2, , frictionRigid RBE2.

5 RBE3 WeldWeldtype selectiontype selectionTimeallotted forTimeallotted is very large incomparison to the other is very large incomparison to the other >>> y, z x>>> y, z 1000>>> 5, 10x>>> y, z 1000>>> 5, 101000>>> 5, 10tedbyconnectingtwonodes,thesoftwarekno wsaboutonlyonetedbyconnectingtwonodes,th esoftwareknowsaboutonlyoneareaofthecross section,mustbedefinedbytheuserasaddition alareaofthecrosssection,mustbedefinedbyt heuserasadditionalboltedjoints,pinjoints ,bearingmodeling, ,pinjoints,bearingmodeling, Introduction To Meshing 2 DElement: Used when two of the dimensions are very large in2 DElement: Used when two of the dimensions are very large in500500500, 300>>Y500, 300>>x, z >>>Xx, z >>> , , ,theelementthicknessspecifiedbytheuseris Mathematically,theelementthicknessspecif iedbytheuserisHence,inordertorepresentth egeometryappropriately,itisnecessaHence, inordertorepresentthegeometryappropriate ly, :Allsheetmetalparts,plastic componentslike Practicalexample.

6 Allsheetmetalparts,plastic componentslike havinga width /thickness ratio > width /thickness ratio > MidSurfaceAnd2 DMeshingLimitationsOf MidSurfaceAnd2 DMeshing2 Dmeshing would lead to a higher approximation ifused for2 Dmeshing would lead to a higher approximation ifused for-variable part thickness-variable part thickness-surfaces are not planner and have different features -surfaces are not planner and have different features 33 Meshing -incomparison to the third to the third >>10mm>>10mm>>>y>>>yelementsareplanar, ,theelementsareplanar, ,thedimension,thickness,hastoprovidedbyt heuserasanadditionaldimension,thickness, instrumentpanels, , 2D meshingisusedforparts e instrumentpanels, , 2D meshingisusedforparts eatures on two on two Introduction To Meshing 3 DElement: used when all three dimensions are comparable3 DElement: used when all three dimensions are comparableYx ~ y ~ zYx ~ y ~ z100 ~ 200 ~ 50X100 ~ 200 ~ 50 XZZP ractical examples: Transmission casing,clutch housing, engine blockPractical examples: Transmission casing,clutch housing, engine blockTractor Components Mesh Tractor Components Mesh Image Source: Altair Calendar 2005 Courtesy : Mahindra and Mahindra Ltd.

7 , Tractor DivisionCourtesy : Mahindra and Mahindra Ltd., Tractor ,hexelementsarepreferredStructuralandfat igueanalysis-Quad,hexelementsarepreferre dCrashandnonlinearanalysis PrioritytomeshflowlinesandbrickCrashandn onlinearanalysis PrioritytomeshflowlinesandbrickMoldflowa nalysis Triangularelementarepreferredoverquadril aMoldflowanalysis Triangularelementarepreferredoverquadril aDynamicanalysis WhenthegeometryisborderlinebetweentheDyn amicanalysis Whenthegeometryisborderlinebetweenthepre ferred over 3D. This is because shell elements being ,theappropriateselectionofelements,Whent imeisnotaconstraint,theappropriateselect ionofelements,Sometimesduetoaverytightde adline,theanalystisforcedtosubmitSometim esduetoaverytightdeadline, or batch Meshing tools could be used instead or batch Meshing tools could be used instead 3 Dmeshing tetras are preferred over 3 Dmeshing tetras are preferred over either coarse meshed or represented approximately are either coarse meshed or represented approximately 44 Meshing -1001002002005050100 ~ 200 ~ 50100 ~ 200 ~ 50block, connecting rod, crank shaft , connecting rod, crank shaft , , ,2 Dshellelementsaretheclassificationof2 Dand3 Dgeometry,2 Dshellelementsareercaptures the mode shapes accurately and with a fewer numberelements,meshflowlines, ,meshflowlines.

8 Of time consuming but structured and good quality providingead of time consuming but structured and good quality providingthenonlythecriticalpartsaremesh edappropriately. Otherparts thenonlythecriticalpartsaremeshedappropr iately. Otherparts ely by 1 Dbeams, springs, concentrated mass, by 1 Dbeams, springs, concentrated mass, Introduction To Meshing CanWeSolveTheSameProblemUsingCanWeSolveT heSameProblemUsingCanWeSolveTheSameProbl emUsingIsitnotpossibletouse3 Delementsforlongslenderbeams(1 DIsitnotpossibletouse3 Delementsforlongslenderbeams(1 Delements for representing bigcasting parts ?elements for representing bigcasting parts ?Thesamegeometrycould be modelledusing 1D,2D,or 3D elements. Thesamegeometrycould be modelledusing 1D,2D,or 3D elements. the accuracy of the results, and the time consumed inthe accuracy of the results, and the time consumed inthe example, consider a cantilever beam witha dimension of 250 For example, consider a cantilever beam witha dimension of 2501 Dbeam model1 Dbeam modelN=2 E=1N=2 E=1 Total DOF =6x 2=12 Total DOF =6x 2=12N=909 E =800N=909 E =800 Total dof =909x 6=5454 Total dof =909x 6=5454 2 Dshell mesh2 Dshell mesh3 DTetra mesh3 DTetra meshN=17,448 E =9,569N=17,448 E =9,569 Total dof =17,448x 3=52,344 Total dof =17,448x 3=52,344 NodesElementsNodesElementsAnalytical---- Analytical----1D211D212D9098002D9098003D 17,4489,5693D17,4489,56955 Meshing -Using1D,2 DAnd3 DElementsUsing1D,2 DAnd3 DElementsUsing1D,2 DAnd3 DElements(1 Dgeometry),forsheetmetalparts(2 Dgeometry),and2 Dshell(1 Dgeometry),forsheetmetalparts(2 Dgeometry)))

9 ,and2 Dshellor 3D elements. Whatmattersisthe numberofelementsand nodes (DOF), or 3D elements. Whatmattersisthe numberofelementsand nodes (DOF), the 250x 20x 5mm that is subjected to a 35 Nforce:of 250x 20x 5mm that is subjected to a 35 Nforce:ElementsStress Displacement ElementsStress N/mm2 Displacement , , Introduction To Meshing HowToDecideElementLengthHowToDecideEleme ntLengthHowToDecideElementLength Basedonpreviousexperiencewithasimilartyp eofproblem(successful Basedonpreviousexperiencewithasimilartyp eofproblem(successful Type of analysis:Linear static analysis could be easily carried out Type of analysis:Linear static analysis could be easily carried out but crash, nonlinear, CFD, or dynamic analysis takes a lot of time. Kbut crash, nonlinear, CFD, or dynamic analysis takes a lot of time. Kelements is is necessary. Hardwareconfigurationandgraphicscardcapa cityoftheavailable Hardwareconfigurationandgraphicscardcapa cityoftheavailablelimit of the nodes that can be satisfactorily handled with the gilimit of the nodes that can be satisfactorily handled with the giSupposeyouareapartofanewlyformedCAEgro up(noclearguidelinesSupposeyouareapartof anewlyformedCAEgroup(noclearguidelinesgr oup):Inthefirstrun, ):Inthefirstrun, ).)

10 Differenceinstrainenergy/maximumstressva lue).HowToStartMeshingHowToStartMeshing1 )SpendASufficientAmountOfTimeStudyingThe 1) )TimeEstimation2) (asmuchas2to3times).inestimationbydiffer entengineers(asmuchas2to3times).ifsomeon eishandlingthejobforthefirsttime,thenhe/ shewillifsomeoneishandlingthejobforthefi rsttime,thenhe/shewillengineeragainandag ain,themeshingtimewouldreducedrasticalle ngineeragainandagain,themeshingtimewould reducedrasticall3)GeometryCheck3)Geometr yCheckGenerallyCADdataisprovidedin*. *. , , Free edges Free edges Scar lines Scar lines Duplicate surfaces Duplicate surfaces Small fillets Small fillets Small holes Small holes Beads Beads Intersection of parts (assembly of components) Intersection of parts (assembly of components)Ifsuppressingfillets,smallhol es,beads,orthegenerationIfsuppressingfil lets,smallholes,beads,orthegenerationthe CADdataprovidedinthewayneededforCAEbythe CADtheCADdataprovidedinthewayneededforCA EbytheCADYes,theoreticallythatwouldbeani dealsituation,butpracticallyYes,theoreti callythatwouldbeanidealsituation,butprac ticallyCADdataisgeneratedkeepinginmindth efinaldrawingtobeCADdataisgeneratedkeepi nginmindthefinaldrawingtobesimultaneousl ytothetoolsandjig/fixturemanufactures,ve ndors,simultaneouslytothetoolsandjig/fix turemanufactures,vendors,Thesimplificati onrequiredforaFEAisunderstoodbetterbyaCA ET hesimplificationrequiredforaFEAisunderst oodbetterbyaCAEspecialtoolsforgeometrycl eanupandsimplification,whichareusuallysp ecialtoolsforgeometrycleanupandsimplific ation,whichareusuallygeometry,surfacingo perationsfailinCADsoftwareanditcouldgeom etry.