Nastran-接触分析

S3-1NAS123,Section3,September2008Copyright2008MSC.SoftwareCorporationSECTION3NUMERICALCONCEPTSINNONLINEARANALYSISS3-2NAS123,Section3,September2008Copyright2008MSC.SoftwareCorporationS3-3NAS123,Section3,September2008Copyright2008MSC.SoftwareCorporation●PartI:NumericalAnalysisofNonlinearBehavior●NonlinearAnalysis:The“Attitude”●IterativeSolutionMethods(NewtonRaphson)●LoadIncrementationandAutomaticTimeStepping●AnalysisConvergence●PartII:LoadControlsandGUIControls●GraphicalUserInterfaceControls●ConstrainedSolutionMethods(Arc-Length)●CostOfNonlinearAnalysisOverviewS3-4NAS123,Section3,September2008Copyright2008MSC.SoftwareCorporationPart1:TheNonlinearAnalysis“Attitude”IterativeSolutionMethodsAnalysisConvergenceS3-5NAS123,Section3,September2008Copyright2008MSC.SoftwareCorporationThe“Attitude”●Interpretation+Simulation=“Idealisation”●Goodidealisationrequires:●Understandingofthestructureanditsgeneralbehaviorunderload●Understandingofthebehaviorthatisofinterest(andthosethatarenot…)●UnderstandingofthemostappropriateFEfeaturestouse●ThisexactingprocessrequiresaninquisitiveEngineerwithagrowingunderstandingofFEAFiniteElementAnalysisisanapproximatetechniqueinwhich“reallife”is:…interpretedbyanEngineerand…simulatedbyappropriatenumericalalgorithmsS3-6NAS123,Section3,September2008Copyright2008MSC.SoftwareCorporationIterativeSolutionMethodsS3-7NAS123,Section3,September2008Copyright2008MSC.SoftwareCorporationIterativeSolutionMethodsPureIncrementationSchemes:•Loadappliedincrementally•Noiterativecorrection•Residualeliminatedonanincrementalbasis•Pathhistory•Stiffnessupdatedincrementally•“Drift”fromtrueequilibriumIncremental-IterativeSchemes:•Loadappliedincrementally•Iterativecorrectiontorestoreincrementalequilibrium•Pathhistory•Stiffnessupdatedincrementallyoriteratively•Newton-RaphsonmethodsS3-8NAS123,Section3,September2008Copyright2008MSC.SoftwareCorporationTheNewtonRaphsonMethod●Steps1-5arethepredictivestages●Steps6-9arethecorrective(iterative)stages●P1neednotequalP2●K0neednotequalK1Example:Predictor–CorrectorMethodS3-9NAS123,Section3,September2008Copyright2008MSC.SoftwareCorporationDisplacement,uUnbalancedLoadsPredictorIterationsP2P1PPu1u2R1R2R3R4Load,PPredictorIterationsExample:IterateuntilloadsbalanceTHENEWTON-RAPHSONALGORITHMS3-10NAS123,Section3,September2008Copyright2008MSC.SoftwareCorporationLoadIncrementationControlTherearethreeprincipalwaystoapplyloading:FFFFNFFiiiinci1Constantloadincrementation(“Fixed”)Variableloadincrementation(“adaptive”)Variableloadincrementation(“adaptive/arc-length”)ThetotalloadisdividedequallyintoanumberofspecifiedsolutionincrementsThenextloadincrementisevaluatedfromthepreviousloadmultipliedbyagrowth/reductionfactorThenextloadincrementisevaluatedfromthepreviousloadincrementmultipliedbythearc-lengthmagnitudeS3-11NAS123,Section3,September2008Copyright2008MSC.SoftwareCorporationLoadIncrementationControlLoadIncrementDisplacementMoresolutioninformationobtainedwhereproblemismostnonlinear.“Fixed”●Givesmore“user”control●Goodformildlynonlinearorwheretheresponseissmooth●AchievedbysettingMaxtimestep=Mintimestep“Adaptive”●Therecommendedmethod●AutomaticallylocatesandhandlessuddennonlinearityDefaultmethodused,controlledbyNLAUTOandNLSTRATbulkdataentries.Whilethismethodisavailable,Adaptiveisthedefaultandhighlyrecommendedmethod.S3-12NAS123,Section3,September2008Copyright2008MSC.SoftwareCorporationTimeScales/AutomaticTimeIncrementation●InNonlinearStaticstimestepsizeisbasedonthe“Desired”numberofiterationstoconverge●Specifiedbyuser(“desired”)●Numberofactualrecyclestoconverge(“actual”)●ifactualdesired=“easy”increment…increasetimestepinnextincrement●ifactual=desired=“target”increment…continuewiththesametimestepinnextincrement●ifactualdesired=“hard”increment…decreasetimestepinnextincrementAutoStepRelativeCriteriaAutoSwitchRobustSolution++=S3-13NAS123,Section3,September2008Copyright2008MSC.SoftwareCorporation0.01.01.0TimeperiodRelativeloadmagnitudeSUMMARYOFJOBINFORMATION:STEPINCATTSEVEREEQUILTOTALTOTALSTEPINCOFDOFIFDISCONITERSITERSTIME/TIME/LPFTIME/LPFMONITORRIKSITERSFREQ1112240.003500.003500.0035001211230.007000.007000.0035001312240.01230.01230.0052501412350.02010.02010.0078751511450.03190.03190.011811611450.04970.04970.017721712570.07620.07620.026581812570.1030.1030.026581911780.1290.1290.0265811011670.1560.1560.0265811112680.1830.1830.0265811211780.2000.2000.025682120880.004540.004540R2210880.008870.004334R2210880.012980.004110RStatusFileOutputTheTimeScale●Notethatinstaticanalysesloadfractioniscalled“time”●Time,whetherphysicallymeaningfulornot(staticprocedures),providesascaleoverwhicha“history”ofevents(loadhistory)isdescribed●“Time”incrementationis(preferably)automaticallycontrolled●SOL600usestheconceptoftimetomonitorloadincrementation–eveninstaticanalyses(typicallyatimeperiodofunity)S3-14NAS123,Section3,September2008Copyright2008MSC.SoftwareCorporationTheTimeScale●Foradaptiveloadincrementation,caremustbetakentoappropriatelydefinetheloadinghistoryineachloadcase●Theloadcaseshouldbedefinedb