ppt1、接触CONT-LA03-DynamicImp

Thefollowingtopicsarecoveredinthislesson.Lessoncontent:DynamicContactusingImplicitIntegration,Appendix3:DynamicContactusingImplicitIntegration,1hour,DynamicContactusingImplicitIntegration,TimeIntegrationIssuesImplicitDynamicsDampingImpactProblemsContactinLinearPerturbationProcedures,TimeIntegrationIssues(1/4),Twotypesofnumericalintegrationschemesareavailableforthedirectsolutionofdynamicsproblems:explicitandimplicit.Comparehowthedisplacementsandvelocitiesattimet+Dtaredefined:Explicit:writtenentirelyintermsofquantitiesknownatorbeforetimet.Thesolution“marchesalong”intime.Implicit:writtenintermsofquantitiesatorbeforetimet+Dt.Nonlinearalgebraicequationsmustbesolvedateachtimeincrement.Someadvantagesanddisadvantagesofeachmethod:Explicit:Convergenceisnotanissue.Themethodisconditionallystabletimeincrementislimited.Implicit:Convergencemustbeobtainedateachincrement.Themethodisunconditionallystablelargetimeincrementscanbeused.,TimeIntegrationIssues(2/4),ExplicitdynamicstimeintegrationMarchforwardintimeusingthecentraldifferencemethodNomatrixinversion(lumpedmass)EachincrementisfastE.g.:1secondanalysistime/incrementfora2millionelementmodelConditionalstability(smallDt)LotsofincrementsE.g.:100,000incrementsfora0.1secondevent,TimeIntegrationIssues(3/4),ImplicitdynamicstimeintegrationMarchforwardintimewithimplicittimeintegrationSolvenonlinearimplicitsystemofequationseachtimeincrementEquationsolverandNewtoniterations(likestatics)ConsistentmassmatrixThetimeintegratorsusedbyAbaqus/StandardareunconditionallystableTimeincrementsizeisgovernedbyconvergencerateandaccuracyComparedtoexplicittimeintegrationHighercostperincrement,butfewerincrements(largerDt)Possibilityoflackofconvergence(residualtolerancesineffect),TimeIntegrationIssues(4/4),InAbaqus/Standardonlytheimplicitintegrationmethodisimplemented.TheHilber-Hughes-Taylor(HHT)method(modifiedtrapezoidalrule)isused(unlesstheapplicationtypeisquasi-static).Incorporatesadjustablenumericaldamping:*DYNAMIC,ALPHA=a,whichselectivelydampsthehighestfrequenciesinthemodel.TheexplicitintegrationmethodisimplementedinAbaqus/Explicit.ThislectureconcentratesondynamicsinAbaqus/Standardfromtheperspectiveofcontactanalysis.ForfurtherinformationonsolvingdynamicproblemswithAbaqus,consulttheAbaqusAnalysisUsersManualorthefollowingtrainingcourses:IntroductiontoAbaqusIntroductiontoAbaqus/StandardandAbaqus/ExplicitLinearDynamicswithAbaqus,ImplicitDynamics(1/7),PossiblemotivationforconsideringuseofthegeneralimplicitdynamicsprocedureDesiretomodeltransienteventsinvolvingsignificantnonlinearityTimeperiodofeventmaybelongerthancouldbeefficientlymodeledwithexplicitdynamicsDesiretoleveragestabilizingeffectsofinertiatoovercomestaticinstabilitiesForexample,overcomeissuesassociatedwithunconstrainedrigidbodymodesinapurelystaticanalysis,ImplicitDynamics(2/7),ImplicitdynamicsinAbaqus:threeclassesofapplicationsTimeincrementationschemedependsondynamicapplicationtypeTransientfidelityapplications(defaultformodelswithoutcontact)*DYNAMIC,APPLICATION=TRANSIENTFIDELITYRequireminimalenergydissipationSmalltimeincrementsrequiredtoaccuratelyresolvethevibrationalresponseofthestructure,andnumericalenergydissipationiskeptataminimumModeratedissipation(defaultformodelswithcontact)*DYNAMIC,APPLICATION=MODERATEDISSIPATIONAmoderateamountofenergyisdissipatedbyplasticity,viscousdamping,orothereffectsAccurateresolutionofhigh-frequencyvibrationsisusuallynotofinterestImprovedconvergenceforanalysesinvolvingcontactQuasi-static*DYNAMIC,APPLICATION=QUASI-STATICTheseproblemstypicallyshowmonotonicbehavior,andinertiaeffectsareintroducedprimarilytoregularizeunstablestaticbehavior,ImplicitDynamics(3/7),ModerateDissipationTransientFidelityQuasi-static,*Dynamic,Application=,Defaultforcontactmodels,Defaultfornoncontactmodels,Intendedforquasi-staticmodeling,1stsetting(default),2ndsetting,3rdsetting,Bouncingdiscexample:,234solverpasses,1277solverpasses,168solverpasses,KineticEnergyComparison,1,2,3,ImplicitDynamics(4/7),“ModerateDissipation”setting(vs.“TransientFidelity”setting)SomeadditionalnumericaldissipationBetterconvergencebehaviorforcontactapplicationsFewersolverpassesReasons:1.Nodirectenforcementofvelocityandaccelerationcompatibilityacrosscontactinterfaces2.Nohalf-incrementresidualtolerance3.DifferentparametersettingsfortheHHTtimeintegrator,ImplicitDynamics(5/7),CommentsonApplication=Quasi-staticMainlyintendedforcasesinwhichastaticsolutionisdesiredbutstabilizingeffectsofinertiaarebeneficialUponconvergencedifficultywithstaticprocedurePerformancevs.Abaqus/ExplicitisproblemdependentAlsoapplicabletosomedynamiceventsDefaultamplitudetypeis“ramp”insteadof“step”LikethegeneralstaticprocedureHighnumericaldissipationBackwardEulertimeintegrator,Originalconfiguration,Crimpingprediction,Wirecrimpingexample,ImplicitDynamics(6/7),*Thehalf-incrementresidualistheout-of-balanceforcethatexistshalfwaythroughatimeincrement.,ImplicitDynamics(7/7),Theincrementationcontrolscanbemodifiedinthestepeditor:,Damping,Stiffnessproportional(beta)RayleighdampinginthematerialoftenimprovesconvergencebehaviorwithoutsignificantlyaffectingresultsStabilizeshigh-frequenciesWhereasinertiaeffectonKhasmosteffectonlowfrequenciesNotactivebydefault,*Material*Damping,Beta=bR,Abaqus/CAE:Propertymodule:materialeditor:MechanicalDamping:Beta:bR,Thisisadifferent“beta”thanthe“beta”associatedwithHHTandNewmarktimeintegrators!,ImpactProblems(1/12),Controllingincrementationinvolvingcontact(impact)Whenchangesinthecontactstateoccur(duetoimpactevents)theimpulseequationisusedtoenforcecompatibilityofvelocitiesandaccelerationsacrossactivecontactinterfaces.Thistypicallyresultsinreducedtimeincrementsizesuponchangesincontactstatus.Bydefaultthedynamicapplicationtypeissetto“moderatedissipation”incaseswherecontactispresentinthemodel.Inthiscaseimpactcalculationsarenotmade.Theimpactcalculationsoccuronlyif:theapplicationtypeisexplicitlysetto“transientfidelity:”*DYNAMIC,APPLICATION=TRANSIENTFIDELITYoriftheIMPACTparameterissetonthe*DYNAMICoption:*DYNAMIC,IMPACT=AVERAGETIME|CURRENTTIME,ImpactProblems(2/12),Theimpactcalculationsoccurwithinanextratimeincrementwithaverysmallsize.SUMMARYOFJOBINFORMATION:MONITORNODE:1DOF:2STEPINCATTSEVEREEQUILTOTALTOTALSTEPINCOFDOFIFDISCONITERSITERSTIME/TIME/LPFTIME/LPFMONITORRIKSITERSFREQ:14010330.02770.02770.001458-3.251411U0330.02770.02770.001735-3.2514120220.02920.02920.001535-3.6014210220.02920.02921.735e-09-3.601431U0220.02920.02920.001735-3.601432U0440.02920.02920.0004336-3.601433U0220.02920.02920.0001084-3.6014340220.02920.02926.091e-06-3.6014410220.02920.02926.091e-06-3.6014510220.02920.02926.091e-06-3.60:Increment42takesplaceinessentiallyzerotime,whichinthiscaseisnotasignofconvergenceproblemsbutratheranindicationthatimpacthasoccurred.,ImpactProblems(3/12),Directusercontrolovertheimpactcalculationisavailable*DYNAMIC,IMPACT=IMPACT=AVERAGETIME(defaultfortransientfidelity)Employsaveragetimeofimpact/releasecutbackstoapproximatelyenforceenergybalanceandmaintainsvelocitiesandaccelerationscompatibleontheactivecontactinterfaceIMPACT=CURRENTTIMEUsesa“marchingthrough”schemewithoutimpact/releasecutbacks.ThevelocitiesandaccelerationsarecompatibleontheactivecontactinterfaceIMPACT=NO(defaultformoderatedissipation)Usesa“marchingthrough”schemewithoutimpact/releasecutbacksandwithoutvelocity/accelerationcompatibilitycomputations,ImpactProblems(4/12),Averagetimeimpactalgorithm,ImpactProblems(5/12),Currenttimeimpactalgorithm,ImpactProblems(6/12),ImpulsecalculationWhentwonodescollide,Abaqusassumesthattheyinstantaneouslyacquirethesamevelocity(“perfectlyplasticimpact”):somelocalmechanism,notmodeled,accountsforthisbehavior.Attheinstantofimpactthedisplacementsandvelocitiesareequal.Themagnitudeofthevelocityafterimpactmustbecalculated.Toobtainthepost-impactvelocity,themomentumbalanceequationmustbesolved:wheret-indicatestimejustpriortoimpactandt+,justafter.,ImpactProblems(7/12),Althoughconservationofmomentumisalwayssatisfied,conservationofenergyisnot.Therewillalwaysbesomeenergylossfromthis“perfectlyplastic”impact.Lossescanbeminimizedbyusinganappropriatelyfinemeshsothatlessmassisassociatedwitheachsurfacenode.,ImpactProblems(8/12),Energylossduringimpactisaphysicalphenomenon,attributabletofourmechanisms:LocalizedinelasticdeformationDissipationofelasticstresswavesasaresultofdampingGrossinelasticdeformationGenerationofsound(usuallyinsignificant),ImpactProblems(9/12),Thefiniteelementmethodallowssomeofthesemechanismstobemodeleddirectly.Considerthemechanismsintermsoftheirlengthscales.Lengthscaleappropriatetofiniteelementmodel:DampingGrossinelasticdeformationLengthscaletoosmallforfiniteelements:LocalizedinelasticdeformationTheperfectlyplasticimpactassumptionindirectlyaccountsforenergylossduetolocalizedinelasticdeformation.Youmustjudgewhetherthelocalenergylossatimpactcanbeattributedtolocaleffectsthatarenotmodeledindetail.,ImpactProblems(10/12),Usethe*ENERGYPRINToptiontomonitortheenergylossasaresultofimpact.Thisprintoutwillappearinthedata(.dat)file:INCREMENTNUMBER42ESTIMATESOFIMPULSEDURINGIMPACTELEMENTNODE1NODE2IMPULSE(PERUNITAREAFORINTER,IRSANDISLELEMENTS)GAP314120.114KINETICENERGYBEFOREIMPACT2.089E+04KINETICENERGYAFTERIMPACT2.088E+04KINETICENERGYLOSTDUETOIMPACT11.6APPROXIMATEENERGYTOTALS-KINETICENERGY2.088E+04RECOVERABLESTRAINENERGY3.443E+03EXTERNALWORK2.626E+04PLASTICDISSIPATION1.924E+03CREEPDISSIPATION0.000E+00VISCOUSDISSIPATION(INDAMPERSETC)0.000E+00ENERGYLOSTATIMPACTS11.6ENERGYTOCONTROLSPURIOUSMODES0.000E+00ENERGYLOSTTHROUGHQUIETBOUNDARIES0.000E+00ELECTROSTATICENERGY0.000E+00TOTALSTRAINENERGY(STRESSPOWER)5.367E+03ENERGYBALANCE2.92,Energylossresultingfromimpactisaccumulatedthroughoutanalysis,Printoutresultingfrom*ENERGYPRINT,ImpactProblems(11/12),Usethe*ENERGYOUTPUToptiontowritetheenergydatatotheoutputdatabasefile.Illustratetheenergylossbycreatinghistoryplotsof:ALLKE:TotalkineticenergyinentiremodelALLKL:EnergylostfromentiremodelasaresultofimpactUsethe*ENERGYFILEoptiontowriteallenergydatatotheresultsfile.,ImpactProblems(12/12),ImpactwithsoftenedcontactWithsoftcontactthechangeinvelocityisdeterminedbytheamountofinterpenetration.Nosuddenjumpsinvelocity.Nomomentumbalanceisrequiredsavescomputationaltime.Nokineticenergyislost.Oftennodeswillbouncebackimmediatelyafterimpactexcessivechattering,causingconvergenceproblemsand/orexcessivelysmalltimeincrements.Use