ls-dyna预应力加载简绍,相当详细

Copyright©2003-2011byLIVERMORESOFTWARETECHNOLOGYCORPORATIONPreload1PreloadsinLS-DYNAIntroductionAnalysisTechniques(General)DynamicRelaxationExplicitImplicitTransientExplicitwithMassDampingImplicitAnalysisBoltPreloadTechniquesThermalInterferenceContactStressinSolidCross-sectionForceinBeamsCopyright©2003-2011byLIVERMORESOFTWARETECHNOLOGYCORPORATIONPreload2Preload-IntroductionSometimesitisimportanttoinduceasteadystatepreloadbeforeperformingatransientdynamicanalysis.Rotatingfanorturbineblades,rotatingflywheelsGravityPressurevesselsortiresShrink-fitpartsStressesinducedbyatorquedboltCopyright©2003-2011byLIVERMORESOFTWARETECHNOLOGYCORPORATIONPreload3ExplicitDynamicRelaxation(DR)ExplicitDRisanoptionaltransientanalysisthattakesplacein‘pseudo-time’(precedesregulartransientanalysis).DRistypicallyusedtopreloadamodelbeforeonsetoftransientloading.Preloadstressesaretypicallyelasticanddisplacementsaresmall.InexplicitDR,thecomputednodalvelocitiesarereducedeachtimestepbythedynamicrelaxationfactor(default=.995).ThusthesolutionundergoesaformofdampingduringDR.Thedistortionalkineticenergyismonitored.WhenthisKEhasbeensufficientlyreduced,i.e.,the“convergencefactor”hasbecomesufficientlysmall,theDRphaseterminatesandthesolutionautomaticallyproceedstothetransientanalysisphase.Alternately,DRcanbeterminatedatapresetterminationtime.Copyright©2003-2011byLIVERMORESOFTWARETECHNOLOGYCORPORATIONPreload4ExplicitDynamicRelaxationDRistypicallyinvokedbysettingparameterSIDRinaloadcurve(*DEFINE_CURVE)to1or2.RamptheloadduringDRphaseandthenholdloadconstantuntilsolutionconvergesMakesureconvergenceoccursafter100%ofpreloadisappliedMaintainthepreloadinsubsequenttransientanalysisphase(useseparateloadcurvewithouttheramp)DRconvergesSIDR=1(DRphase)SIDR=0(transientphase)Copyright©2003-2011byLIVERMORESOFTWARETECHNOLOGYCORPORATIONPreload5*CONTROL_DYNAMIC_RELAXATION*CONTROL_DYNAMIC_RELAXATIONparametersIterationsbetweenconvergencecheck(default=250)Alsoaffectsoutputintervalfor“d3drlf”Convergencetolerance(default0.001)RatioofdistorsionalKEatconvergencetopeakdistorsionalKESmallervalueresultsinconvergedsolutionnearertosteadystatebutrunwilltakelongertogetthereDynamicrelaxationfactor(default=0.995)ReductionfactorfornodalvelocitieseachtimestepIfvalueistoosmall,modelneverreachsteadystateduetooverdampingOptionalterminationtimeforDR(default=infinity)DRwillstopiftimereachesDRTERMevenifconvergencecriterionnotsatisfiedTimestepscalefactorusedduringDRExplicitDynamicRelaxationCopyright©2003-2011byLIVERMORESOFTWARETECHNOLOGYCORPORATIONPreload6*CONTROL_DYNAMIC_RELAXATIONparametersIDRFLGFlagtoactivateDR(notrequiredifDRisactivatedwith*DEFINE_CURVE)Setto2,willinvokeacompletelydifferentandfasterinitializationapproach…InitializationbyPrescribedGeometry.Requiressupplementalinputfilecontainingnodaldisplacementsandrotations(“m=filename”onexecutionline).•Suchafiledrdisp.sifiswrittenatconclusionofstandardDRrun.•Ifnodalrotationsarenotincludedinfile,methodisinvalidforbeamsandshells.LS-DYNA®runsashorttransientanalysisof100timestepstopreloadthemodelbyimposingthenodaldisplacementsandrotations.Solutionthenproceedswithregulartransientanalysis.Setto5,activatesimplicitmethodforsolutionofpreloadedstateMustalsosetDRTERMtosignalendofDRphase.*CONTROL_IMPLICIT...providecontrolsonimplicitphase.*CONTROL_DYNAMIC_RELAXATIONDynamicRelaxationCopyright©2003-2011byLIVERMORESOFTWARETECHNOLOGYCORPORATIONPreload7OutputRelatedtoDynamicRelaxationASCIIoutputfilesareNOTwrittenduringDRphase,e.g.,glstat,matsum,rcforc,etc.Thebinaryd3thdtfilecanbeusedifIDRFLG=-1.Binarydatabase,d3drlf,iswrittenbyincludingcommand*DATABASE_BINARY_D3DRLF.Setoutputintervalto1.ThiswillcauseastatetobewritteneachtimeconvergenceischeckedduringDRPlottingtimehistoriesfromd3drlfwithLS-PrePost®allowsusertoconfirmsolutionisnearsteadystaterelaxfileisautomaticallywrittenandcontainsrecordofconvergencehistory.DatacanbeplottedwithLS-PrePost.drdisp.sifcontainsnodaldisplacementsandrotationsatconclusionofDRphase.DynamicRelaxationCopyright©2003-2011byLIVERMORESOFTWARETECHNOLOGYCORPORATIONPreload8OutputRelatedtoExplicitDynamicRelaxationExplicitDynamicRelaxationDynamicRelaxationinformationiswrittentothescreen.ThetransientphasestartswhentheconvergencetoleranceoraSpecifiedterminationtimeisreached.ConvergenceplotfromrelaxfileKineticEnergyplotfromrelaxfileCopyright©2003-2011byLIVERMORESOFTWARETECHNOLOGYCORPORATIONPreload9TypicalLoadsDuringDynamicRelaxationGravityloadsandcentrifugalloads(spinningbodies)areimposedusing*LOAD_BODY_option.LCIDandLCIDDRareseparatecurvesfortransientphaseandDRphase,respectively.Thermalstressescanbeimposedusing*LOAD_THERMAL_LOAD_CURVE.Parts,e.g.,bolts,definedwithacoefficientofthermalexpansionwillhavethermalstressesimposed.LCIDandLCIDDRareseparatecurvesfortransientphaseandDRphase,respectively.OtherloadtypesorboundaryconditionsareappliedduringDRifSIDRincorresponding*DEFINE_CURVEissetto1or2.Example:*LOAD_SEGMENT,*BOUNDARY_PRESCRIBED_MOTION.*CONTACT_..._INTERFERENCEimposesloadassociatedwi