ls-dyna预应力加载简绍-相当详细.ppt

ls-dyna预应力加载简绍-相当详细.ppt

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PreloadsinLS-DYNA,IntroductionAnalysisTechniques（General）DynamicRelaxationExplicitImplicitTransientExplicitwithMassDampingImplicitAnalysisBoltPreloadTechniquesThermalInterferenceContactStressinSolidCross-sectionForceinBeams,Preload-Introduction,Sometimesitisimportanttoinduceasteadystatepreloadbeforeperformingatransientdynamicanalysis.Rotatingfanorturbineblades,rotatingflywheelsGravityPressurevesselsortiresShrink-fitpartsStressesinducedbyatorquedbolt,ExplicitDynamicRelaxation（DR）,ExplicitDRisanoptionaltransientanalysisthattakesplaceinpseudo-time（precedesregulartransientanalysis）.DRistypicallyusedtopreloadamodelbeforeonsetoftransientloading.Preloadstressesaretypicallyelasticanddisplacementsaresmall.InexplicitDR,thecomputednodalvelocitiesarereducedeachtimestepbythedynamicrelaxationfactor（default=.995）.ThusthesolutionundergoesaformofdampingduringDR.Thedistortionalkineticenergyismonitored.WhenthisKEhasbeensufficientlyreduced,i.e.,the“convergencefactor”hasbecomesufficientlysmall,theDRphaseterminatesandthesolutionautomaticallyproceedstothetransientanalysisphase.Alternately,DRcanbeterminatedatapresetterminationtime.,ExplicitDynamicRelaxation,DRistypicallyinvokedbysettingparameterSIDRinaloadcurve（*DEFINE_CURVE）to1or2.RamptheloadduringDRphaseandthenholdloadconstantuntilsolutionconvergesMakesureconvergenceoccursafter100%ofpreloadisappliedMaintainthepreloadinsubsequenttransientanalysisphase（useseparateloadcurvewithouttheramp）,*CONTROL_DYNAMIC_RELAXATION,*CONTROL_DYNAMIC_RELAXATIONparametersIterationsbetweenconvergencecheck（default=250）Alsoaffectsoutputintervalfor“d3drlf”Convergencetolerance（default0.001）RatioofdistorsionalKEatconvergencetopeakdistorsionalKESmallervalueresultsinconvergedsolutionnearertosteadystatebutrunwilltakelongertogetthereDynamicrelaxationfactor（default=0.995）ReductionfactorfornodalvelocitieseachtimestepIfvalueistoosmall,modelneverreachsteadystateduetooverdampingOptionalterminationtimeforDR（default=infinity）DRwillstopiftimereachesDRTERMevenifconvergencecriterionnotsatisfiedTimestepscalefactorusedduringDR,ExplicitDynamicRelaxation,*CONTROL_DYNAMIC_RELAXATIONparametersIDRFLGFlagtoactivateDR（notrequiredifDRisactivatedwith*DEFINE_CURVE）Setto2,willinvokeacompletelydifferentandfasterinitializationapproachInitializationbyPrescribedGeometry.Requiressupplementalinputfilecontainingnodaldisplacementsandrotations（“m=filename”onexecutionline）.Suchafiledrdisp.sifiswrittenatconclusionofstandardDRrun.Ifnodalrotationsarenotincludedinfile,methodisinvalidforbeamsandshells.LS-DYNArunsashorttransientanalysisof100timestepstopreloadthemodelbyimposingthenodaldisplacementsandrotations.Solutionthenproceedswithregulartransientanalysis.Setto5,activatesimplicitmethodforsolutionofpreloadedstateMustalsosetDRTERMtosignalendofDRphase.*CONTROL_IMPLICIT.providecontrolsonimplicitphase.,*CONTROL_DYNAMIC_RELAXATION,DynamicRelaxation,OutputRelatedtoDynamicRelaxation,ASCIIoutputfilesareNOTwrittenduringDRphase,e.g.,glstat,matsum,rcforc,etc.Thebinaryd3thdtfilecanbeusedifIDRFLG=-1.Binarydatabase,d3drlf,iswrittenbyincludingcommand*DATABASE_BINARY_D3DRLF.Setoutputintervalto1.ThiswillcauseastatetobewritteneachtimeconvergenceischeckedduringDRPlottingtimehistoriesfromd3drlfwithLS-PrePostallowsusertoconfirmsolutionisnearsteadystaterelaxfileisautomaticallywrittenandcontainsrecordofconvergencehistory.DatacanbeplottedwithLS-PrePost.drdisp.sifcontainsnodaldisplacementsandrotationsatconclusionofDRphase.,DynamicRelaxation,OutputRelatedtoExplicitDynamicRelaxation,ExplicitDynamicRelaxation,DynamicRelaxationinformationiswrittentothescreen.ThetransientphasestartswhentheconvergencetoleranceoraSpecifiedterminationtimeisreached.,Convergenceplotfromrelaxfile,KineticEnergyplotfromrelaxfile,TypicalLoadsDuringDynamicRelaxation,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_._INTERFERENCEimposesloadassociatedwithgeometricinterference.*INITIAL_.（moreonthatlater）,DynamicRelaxation,ExplicitDynamicRelaxation,ExampleGravityLoadingon