ANSYS 英文实用培训教程

ENSC895Assignment3Tutorial

Lastupdatedon:Feb25th,

Inthislab,studentswilllearnthebasictechniquesofFEAanalysis.AstaticstructuralanalysiswillbeperformedonaracksystemusingANSYSworkbench.Geometrysimplificationwillbeintroducedtothestudents.Severalmeshtechniqueswillbebrieflyintroducedtothestudents.Howevermappedmeshingisthecorelearningobjective.Thelabwillalsointroducethestudentswithbasicpost-processingtechniquesneededtointerprettheanalysisresults.

Learningobjectives:

Mid-surfacetechnique:studentshavetolearnhowtoextractthemid-surfacetoproducehighqualitymesh.Theruleofthumbisthataslongasthethicknessis1/5ofthewidthorlength,thebodycanbesimplifiedtosurfacebody.Surfacebodyusesplaneorshellelementssuchassolid186orshell181.However,thestudentsdon’thavetoworryaboutwhichelementstoselectfromsinceANSYSwillautomaticallyselectthem.Therearetwowaystoextractmid-surfaces,seetutorialsfordetails.

Learnbasicdefeaturingtechniques:Certainunnecessarydetailsshouldberemovedfromtheanalysisinordertoobtainbettermeshingeffects.Forexample,filletsandchamfersthatdon’tplaymajorrolesinFEAanalysisinmanycasescanbeignoredtogeneratebetterlocalmesh.Studentscandoacomparativestudytoseetheeffectiftimepermits.

Numberofdivisionspercycle:Accordingtocertainindustrystandard,thecirclehastobedividedintoatleast12elements.NormallyANSYSversion14.5willautomaticallydetectanddividethecircleto12elements.Ifnot,onecandoitmanually.Seedetailsfromthetutorials.

BondedcontactwithMPCalgorithm:Inthisassignmentallcontactswillbeautomaticallygenerated.Butsomegeometricalpreprocessingisneededinordertohaveeffectivecontacts.

Convergencestudy:Ameshindependentstudyshouldbeperformedonthestructuretoseehowmeshqualitiescanaffectthefinalresults.Withtheimprovementofmeshthestressvalueshouldapproachasteadystatemeaningitsvalueshouldbewithin5%.

Checkreactions:LearnhowtocheckthereactionsafteraFEAanalysishasbeenperformed.Forexample,three1000Nforcesareaddedondifferentlevelandthereactionatitsboundaryshouldbebalancedforthestructuretobeinequilibrium.

EnteringANSYS

DoubleclickonANSYSworkbenchfromdesktop.

OnceyouhaveenteredANSYSworkbenchdragStaticStructuralfromtheAnalysisSystemtotheblankareacalledontheright.ThendoubleclickonGeometrytoaccessDM(DesignModeler).

SelectMillimeterasthedesiredlengthunit.

BriefIntroductiontosomefunctionsinDM(DesignModeler)

ThefunctionsbelowintheredboxesarethecommonlyusedfunctionsinANSYSpreprocessing.Thesefunctionsareprimarilyusedforgeometrysimplifications.Geometrysimplificationisoneofthemostimportanttasksinpreprocessing.ProperlysimplifiedgeometrycangreatlyimprovethequalityofmeshandthusresultspredictedbytheFEAanalysis.

Mid-Surface:Itisusedtoextractthemiddle-surface.Whenabodycanbeconsideredasaplateorshell(itsshortestdimensionisthe1/5ofotherdimensions),normallyitshouldbesimplified.I

Thin/Surface:ThisisabackupchoiceforMid-SurfaceasMid-Surfacefailstoworksometimes.Itcanalsobeusedtoachieveothertaskssuchasformingacavity.

FaceDelete:Thisisusedtodeleteunnecessaryfacesinordertoimprovemeshquality.Unnecessarydetailsoftenimpedeonefromproducinghighqualitymesh.

EdgeDelete:SameasFaceDelete,butitisforoperationsonedges.

NewPlane:Userscanestablishnewplanesforallkindsofpurposes.However,inthisexercise,itisprimarilyusedasreferenceplaneforcutting/slicing.

Slice:Thepurposeofslicingoperationismultiple.InthisanalysisSliceoperationsareneededinordertogeneratemoremappableregions.Withmappableregions,thequalityofmeshshouldbehigher.

Mappableregions:Mappableregionsarethosesurfaceareasonwhichmappedmeshcanbegenerated.Mappedmeshestypicalhavehighqualityandeffectiveness.Areascoveredbymappedmeshtypicallylooksmoreregularintermsoftheshapeofthemesh.Usemappedsurfacemeshwheneverapplicable.

Doubleclickonengineeringdata.

First,clickonEngineeringDataSources.ThenclickonGeneralMaterialstoseealistofcommonlyusedengineeringmaterials.ThenmoveontoOutlineofgeneralmaterialsandclickontheaddsign.AddAluminumAlloyforlateruse.(Steelisdefaultedmaterialwhichyoudon’thavetoadd)GobacktotheDM.

DoubleclickonGeometrytoaccessANSYSDM.

ImportgeometryintoANSYSworkbench:

ClickonfileandselectImportExternalGeometryFile.Thelocationoftheparasolidgeometry(x_t)willbegiventoyou.

Thegeometrywilllooklikethisifitisimportedcorrectly.

ExtractingMiddleSurfaces

Mid-surfacecommandwillbeusedtoextractmiddlesurfaceofthesheetmetal.Selectfacepairsbyclickingonthefrontandbacksideofthecolumnbar.Aftersuccessfullyselected,itwillbehighlightedinpurple.

However,inordertoselectasmanylegitimatesurfacebodiesaspossible,onecanexploititsauto-selectioncapabilitybychangingtheselectionmethodfrommanualtoautomatic.Noteyoushouldclickon“Findingsurfacepairsnow”onceinorderforthistowork.Thenallavailablesurfacebodieswillbeselectedallatoncewhichwillsaveyouconsiderableamountoftime.

ThereareoccasionsthatMid-surfacewillfailtoworkduetothecomplexityofthegeometry.Fortunately,thereisanothermethodwecanuseinordertobypassthisissue.Thin/SurfacecanbeusedasatooltoextractsurfacebodywhileMid-surfacefailstowork.Clickonthesurfacebodieswhileholdingthectrlkeythisallowsyoutoselectasmanysurfaceasyoumightneed.ChangetheSelectionTypetoFacestoKeepasindicatedbelow.Sincethebottomplateshavethicknessof3mm,inordertoserveasmiddlesurfacesthefaceoffsetshouldbehalfofitwhichis1.5mm.

Defeaturing

NormallygeometriesimportedfromCADsoftwarearetoocomplicatedandhavetoomanydetailstocapture.AsaFEAanalyst,youhavetoknowhowtoremoveunnecessarydetailsasitwillimprovethequalityofmesh.

Surface-deleteisatechniquetodeleteunwantedsurfaces.Forexample,inmanycasesfilletsandchamfersdon’tplayamajorroleinstressanalysisandthuscanbedeleted.

Edge-deleteissimilartoSurface-deleteinwhichitremovesunnecessaryedgesinsteadofsurfaces.

Settingupthethickness:WhenThin/Surfaceisusedtoextractmiddlesurfaceitwillloseinformationonitsthickness.GotoANSYSDesignSimulation(DS)bydoubleclickingonModel.All“part3”arebottomholdingplates,itshouldbenotedthat“part3”arewithquestionmarksbeforesetup.Selectallof“part3”andsetthethicknessto3mm.

Thenextstepisquitecrucialforgeneratinghighqualitymesh.Inordertoproducehighqualitymesh,thegeometryshouldbemadetobemappable(SometimesSweepableinthecaseofsolids).Inordertohaveasmanymappableregionaspossible,Slicefunctionisusedtoseparatethegeometrytosimplershapesandthusmorelikelytobemappable.

Slicecanbeperformedundertheconditionthatthegeometryorapartofthatgeometryisfrozen.WhilethegeometryisfirstimportedtotheDM,itisdefaultedtobefrozen.Thereforeslicecanbeappliedtoeachbodydirectly.

Thereareseveralslicingmethods.Commonlyusedinthisexercisearetwo:1)SlicebySurface;2)Slicebyplane.

SlicebySurface:Selectthesurfacethatyouwanttouseasatoolsurface.ClickonSliceandchangeSliceTypetoSlicebySurfaceandapply.Asindicatedbelow,thegeometrywillbeslicedaboutthetoplevelsurface.Dothisrepeatedlyfor3differentlevels.

SlicebyPlane:Inorderforthisslicingmethodtowork,anewcoordinatesystemneedstobeconstructed.Clickontocreateanewcoordinatesystem.Thenewcoordinatesystemwillbeestablishedonthecorner.

Inorderforslicingplanetowork,onehastore-orientthecoordinatesystemsuchthattheredandgreenaxisformingtheplaneofslicing.Inotherwords,slicingplanewillbeperpendiculartotheblueaxis.

Thenewcoordinatesystemwillbeshown.ChangeTypetoFromPointandNormal.Aspoint-normalmethodwillbethemostconvenientwaytoconstructacoordinate.

Basepointwillbetheoriginofthecoordinatesystemandclickonthevertexasindicatedbelow.ClickonNormalDefinedbyandthengotogeometrytoclickanaxisthatyouwanttospecifyasthenormalaxis.Abigredarrowwillbeshowninthescreentoindicatethedirectionyourselectednormalline.Itdoesn’tmatterastowhatdirectionthebluearrowispointingat,aslongastheredandgreenaxesformtheplaneofcuttingitshouldbeworkingcorrectly.

Thenextstepistousethecoordinatesystemthatyoujustcreatedasareferencetoslicetheplane.

SelectSlicefunctionandchoosetheSliceTypeasSlicebyPlanethistime.ChangetheBasePlanetotheplanethatyouwanttosliceabout.(Normallyifyouhavejustcreatedacoordinatesystem,itwillbedefaultedtoBasePlane.Clickongeneratetoseetheeffect(youcanpressF5aswell).

Createacoordinatesystemagainforanothercornerthistime.Justrepeattheproceduredescribedaboveuntilall4sideshavebeencovered.

Andthenuseslicebasedonthecoordinatesystemjustcreated.

Thisiswhatitlookslikewhenyouhaveslicedtwosides.

If4sidesareslicescorrectly,youshouldgeometryshouldresembletheoneshownbelow.

Createanewcoordinatesystemasshown.

Slicebasedonthecoordinatejustcreated.

Ifyouhavedoneitrightuptothispoint,thestructureshouldlooklike:

Selectallsurfacebodyandputthemallinthepart.ThisallowsANSYStoautomaticallysharethetopologyofnodes.Notealsothatthesurfacebodyandsolidcannotbeputintoonepart.Inthiscase,thereisnosolidbody.

Refreshthefile

Selectallofpart1andassignittoAluminumAlloy

Meshing

ForaFEAengineer,70%-80%oftimeisallocatedtoproducinghighqualitymesh.Thequalityofmeshwilldirectlyaffecttheaccuracyoftheanalysis.FEAcanbeveryaccurateprovidethatmeshisgoodandboundaryconditionsaresetupcorrectly.

InDS,onecanstartbyclickingUpdateandthenANSYSwillautomaticallygenerateameshforyouandthenyoucanchangetheelementsizeandshapetoimproveyourmesh.Howeverthereisanotherbettertogeneratemeshespeciallyforsheetmetalswithregularshapes.OnecanuseMappedmeshtogreatlyimprovethequalityofthemesh.Asamatteroffact,alltheeffortonslicingthestructureisactuallytoincreasethenumberofMappableregionsandthushigherquality.

First,rightclickonMeshandthenmovethecursortoshowandselectMappableFaces.ThisactionwillindicatetheMappablefaces.Notethatyoucanselectasmanymappablesurfaceasyouwanthowevernotallofthemwillwork.TheonesthatareworkingareshowninMappableFaces.

Oncethemappedfacesareselected,clickonMeshControlandthenclickonMappedFaceMeshing.OncethegeometryforMappedFaceMeshingisselected,clickupdatetostartmeshing.

Hereisadetailedviewafterthestructureissuccessfullymeshed.

Applyboundaryconditionsatthebottomholdingplatesatfourcorners.TheboundaryconditionisFixedSupport.

Applyloadsonthestructure.Eachlevelisloadeduniformlywith1000Nroughly(100kg).

Boundaryconditionandloads:

Sincethedesignatedextremeloadingconditionwillinvolvelargedeflectionespeciallyforsoftermaterialsuchasaluminumalloy.Therefore,turninglargedeflectiononwillresultinamoreaccurateanalysis.

ClickonSolvetostartsolving:

Post-processing

VonMises(VM)Stress(overallview)

Changethevaluejustbelowtheredboxto250MPawhichisthetensileyieldstrengthforthesteel.Thismeanswhereverthestressvaluesareabove250MPatheywillbeindicatedbytheredareathatwaywewillknowwhatlocationwillhavehighstressconcentrationandthuslikelytofail.Fortheoverallview,youdon’thavetoconsiderthestressdevelopedinthealuminummaterials,sincesteelcolumnsaretheprimaryloadbearingcomponentsinthisstructure.

Notethatthecolumnsaretheactualload-bearingcomponentintheanalysis.Thusadetailedviewonthecolumnisoftentimesnecessary.SelectthecolumnsfromthegeometryandjustshowtheVMstresswithrespecttothesteelcolumns.

Amagnifiedviewonwherethelocalstresshasexceededthetensileyieldstressofthesteel.

Verificationbycheckingthereactionforces

ItisoftentimesnecessarytovalidatetheresultsobtainedfromFEA