86ANSYS非线性静力分析步骤帮助学习Word文件下载.docx

86ANSYS非线性静力分析步骤帮助学习Word文件下载.docx

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∙SetAdditionalSolutionOptions

∙ApplytheLoads

∙SolvetheAnalysis

∙ReviewtheResults

∙TerminatingaRunningJob;

Restarting

8.6.1. 

BuildtheModel

Thisstepisessentiallythesameforbothlinearandnonlinearanalyses,althoughanonlinearanalysismightincludespecialelementsornonlinearmaterialproperties.SeeUsingNonlinear（Changing-Status）Elements,andModelingMaterialNonlinearities,formoredetails.Ifyouranalysisincludeslarge-straineffects,yourstress-straindatamustbeexpressedintermsoftruestressandtrue（orlogarithmic）strain.FormoreinformationonbuildingmodelsinANSYS,seetheModelingandMeshingGuide.

AfteryouhavecreatedamodelinANSYS,yousetsolutioncontrols（analysistype,analysisoptions,loadstepoptions,andsoon）,applyloads,andsolve.Anonlinearsolutionwilldifferfromalinearsolutioninthatitoftenrequiresmultipleloadincrements,andalwaysrequiresequilibriumiterations.Thegeneralprocedureforperformingthesetasksfollows.SeeSampleNonlinearAnalysis（GUIMethod）forasampleproblemthatwalksyouthroughaspecificnonlinearanalysis.

8.6.2. 

SetSolutionControls

Settingsolutioncontrolsforanonlinearanalysisinvolvesthesameoptionsandmethodofaccess（theSolutionControlsdialogbox）asthoseusedforalinearstructuralstaticanalysis.Foranonlinearanalysis,thedefaultsettingsintheSolutionControlsdialogboxareessentiallythesamesettingsemployedbytheautomaticsolutioncontrolmethoddescribedinRunningaNonlinearAnalysisinANSYS.SeethefollowingsectionsinStructuralStaticAnalysis,withexceptionsnoted:

∙AccesstheSolutionControlsDialogBox

∙UsingtheBasicTab

∙TheTransientTab

∙UsingtheSol'

nOptionsTab

∙UsingtheNonlinearTab

∙UsingtheAdvancedNLTab

8.6.2.1. 

UsingtheBasicTab:

SpecialConsiderations

Specialconsiderationsforsettingtheseoptionsinanonlinearstructuralstaticanalysisinclude:

∙WhensettingANTYPEandNLGEOM,chooseLargeDisplacementStaticifyouareperforminganewanalysis.（But,keepinmindthatnotallnonlinearanalyseswillproducelargedeformations.SeeUsingGeometricNonlinearitiesforfurtherdiscussionoflargedeformations.）ChooseRestartCurrentAnalysisifyouwanttorestartafailednonlinearanalysis.Youcannotchangethissettingafterthefirstloadstep（thatis,afteryouissueyourfirstSOLVEcommand）.Youwillusuallychoosetodoanewanalysis,ratherthanarestart.RestartsarediscussedintheBasicAnalysisGuide.

∙Whenworkingwithtimesettings,rememberthattheseoptionscanbechangedatanyloadstep.See"

Loading"

intheBasicAnalysisGuideformoreinformationontheseoptions.Advancedtime/frequencyoptions,inadditiontothoseavailableontheSolutionControlsdialogbox,arediscussedinAdvancedLoadStepOptionsYouCanSetontheSolutionControlsDialogBox.

Anonlinearanalysisrequiresmultiplesubsteps（ortimesteps;

thetwotermsareequivalent）withineachloadstepsothatANSYScanapplythespecifiedloadsgraduallyandobtainanaccuratesolution.TheNSUBSTandDELTIMcommandsbothachievethesameeffect（establishingaloadstep'

sstarting,minimum,andmaximumstepsize）,butbyreciprocalmeans.NSUBSTdefinesthenumberofsubstepstobetakenwithinaloadstep,whereasDELTIMdefinesthetimestepsizeexplicitly.Ifautomatictimesteppingisoff[AUTOTS],thenthestartingsubstepsizeisusedthroughouttheloadstep.

∙OUTREScontrolsthedataontheresultsfile（Jobname.RST）.Bydefault,onlythelastsubstepiswrittentotheresultsfileinanonlinearanalysis.

Only1000resultssets（substeps）canbewrittentotheresultsfile,butyoucanusethecommand/CONFIG,NREStoincreasethelimit（seetheBasicAnalysisGuide）.

8.6.2.2. 

AdvancedAnalysisOptions分析选项YouCanSetontheSolutionControlsDialogBox

ThefollowingsectionsprovidemoredetailaboutsomeoftheadvancedanalysisoptionsthatyoucansetontheSolutionControlsdialogbox.

8.6.2.2.1. 

EquationSolver

ANSYS'

automaticsolutioncontrolactivatesthesparsedirectsolver（EQSLV,SPARSE）formostcases.OtheroptionsincludethePCGandICCGsolvers.Forapplicationsusingsolidelements（forexample,SOLID92orSOLID45）,thePCGsolvermaybefaster,especiallyfor3-Dmodeling.

IfusingthePCGsolver,youmaybeabletoreducememoryusageviatheMSAVEcommand.TheMSAVEcommandtriggersanelement-by-elementapproachforthepartsofthemodelthatuseSOLID45,SOLID92,SOLID95,SOLID185,SOLID186,SOLID187SOLID272,SOLID273,and/orSOLID285elementswithlinearmaterialproperties.（MSAVEdoesnotsupportthelayeredoptionoftheSOLID185andSOLID186elements.）TouseMSAVE,youmustbeperformingastaticoramodalanalysiswithPCGLanczosenabled.WhenusingSOLID185,SOLID186,and/orSOLID187,onlysmallstrain（NLGEOM,OFF）analysesareallowed.Otherpartsofthemodelthatdonotmeettheabovecriteriaaresolvedusingglobalassemblyforthestiffnessmatrix.MSAVE,ONcanresultinamemorysavingsofupto70percentforthepartofthemodelthatmeetsthecriteria,althoughthesolutiontimemayincreasedependingonthecapabilitiesofyourcomputerandtheelementoptionsselected.

Thesparsedirectsolver,insharpcontrasttotheiterativesolversincludedinANSYS,isarobustsolver.AlthoughthePCGsolvercansolveindefinitematrixequations,whenthePCGsolverencountersanill-conditionedmatrix,thesolverwilliteratetothespecifiednumberofiterationsandstopifitfailstoconverge.Whenthishappens,ittriggersbisection.Aftercompletingthebisection,thesolvercontinuesthesolutioniftheresultingmatrixiswell-conditioned.Eventually,theentirenonlinearloadstepcanbesolved.

UsethefollowingguidelinesforselectingeitherthesparseorthePCGsolverfornonlinearstructuralanalysis:

∙Ifitisabeam/shellorbeam/shellandsolidstructure,choosethesparsedirectsolver.

∙Ifitisa3-DsolidstructureandthenumberofDOFisrelativelylarge（thatis,200,000ormoreDOF）,choosethePCGsolver.

∙Iftheproblemisill-conditioned（triggeredbypoorelementshapes）,orhasabigdifferenceinmaterialpropertiesindifferentregionsofthemodel,orhasinsufficientdisplacementboundaryconstraints,choosethesparsedirectsolver.

8.6.2.3. 

AdvancedLoadStepOptions载荷步选项YouCanSetontheSolutionControlsDialogBox

ThefollowingsectionsprovidemoredetailaboutsomeoftheadvancedloadstepoptionsthatyoucansetontheSolutionControlsdialogbox.

8.6.2.3.1. 

AutomaticTimeStepping

automaticsolutioncontrolturnsautomatictimesteppingon[AUTOTS,ON].Aninternalauto-timestepschemeensuresthatthetimestepvariationisneithertooaggressive（resultinginmanybisection/cutbacks）nortooconservative（timestepsizeistoosmall）.Attheendofatimestep,thesizeofthenexttimestepispredictedbasedonfourfactors:

∙Numberofequilibriumiterationsusedinthelasttimestep（moreiterationscausethetimestepsizetobereduced）

∙Predictionsfornonlinearelementstatuschange（timestepsizesaredecreasedwhenastatuschangeisimminent）

∙Sizeoftheplasticstrainincrement

∙Sizeofthecreepstrainincrement

8.6.2.3.2. 

ConvergenceCriteria

Theprogramwillcontinuetodoequilibriumiterationsuntiltheconvergencecriteria[CNVTOL]aresatisfied（oruntilthemaximumnumberofequilibriumequationsisreached[NEQIT]）.Youcandefinecustomcriteriaifthedefaultsettingsarenotsuitable.

automaticsolutioncontrolusesL2-normofforce（andmoment）tolerance（TOLER）equalto0.5%,asettingthatisappropriateformostcases.Inmostcases,anL2-normcheckondisplacementwithTOLERequalto5%isalsousedinadditiontotheforcenormcheck.Thecheckthatthedisplacementsarelooselysetservesasadouble-checkonconvergence.

Bydefault,theprogramwillcheckforforce（and,whenrotationaldegreesoffreedomareactive,moment）convergencebycomparingthesquarerootsumofthesquares（SRSS）oftheforceimbalancesagainsttheproductofVALUE*TOLER.ThedefaultvalueofVALUEistheSRSSoftheappliedloads（or,forapplieddisplacements,oftheNewton-Raphsonrestoringforces）,orMINREF（whichdefaultsto0.01）,whicheverisgreater.ThedefaultvalueofTOLERis0.005.IfSOLCONTROL,OFF,TOLERdefaultsto0.001andMINREFdefaultsto1.0forforceconvergence.

Youshouldalmostalwaysuseforceconvergencechecking.Youcanalsoadddisplacement（and,whenapplicable,rotation）convergencechecking.Fordisplacements,theprogrambasesconvergencecheckingonthechangeindeflections（Δu）betweenthecurrent（i）andtheprevious（i-1）iterations:

Δu=ui-ui-1.

Note:

Ifyouexplicitlydefineanycustomconvergencecriteria[CNVTOL],theentiredefaultcriteriawillbeoverwritten.Thus,ifyoudefinedisplacementconvergencechecking,youwillhavetoredefineforceconvergencechecking.（UsemultipleCNVTOLcommandstodefinemultipleconvergencecriteria.）

Usingtighterconvergencecriteriawillimprovetheaccuracyofyourresults,butatthecostofmoreequilibriumiterations.Ifyouwanttotighten（orloosen,whichisnotrecommended）yourcriteria,youshouldchangeTOLERbyoneortwoordersofmagnitude.Ingeneral,youshouldcontinuetousethedefaultvalueofVALUE;

thatis,changetheconvergencecriteriabyadjustingTOLER,notVALUE.YoushouldmakecertainthatthedefaultvalueofMINREF=0.001makessenseinthe