2019ls-dyna预应力加载简绍相当详细课件.ppt

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1、PreloadsinLS-DYNAIntroductionAnalysisTechniques(General)DynamicRelaxationExplicitImplicitTransientExplicitwithMassDampingImplicitAnalysisBoltPreloadTechniquesThermalInterferenceContactStressinSolidCross-sectionForceinBeamsPreload-IntroductionSometimesitis

2、importanttoinduceasteadystatepreloadbeforeperformingatransientdynamicanalysis.Rotatingfanorturbineblades,rotatingflywheelsGravityPressurevesselsortiresShrink-fitpartsStressesinducedbyatorquedboltExplicitDynamicRelaxation(DR)ExplicitDRisanoptionaltransient

3、analysisthattakesplacein‘pseudo-time’(precedesregulartransientanalysis).DRistypicallyusedtopreloadamodelbeforeonsetoftransientloading.Preloadstressesaretypicallyelasticanddisplacementsaresmall.InexplicitDR,thecomputednodalvelocitiesarereducedeachtimestepb

4、ythedynamicrelaxationfactor(default=.995).ThusthesolutionundergoesaformofdampingduringDR.Thedistortionalkineticenergyismonitored.WhenthisKEhasbeensufficientlyreduced,i.e.,the“convergencefactor”hasbecomesufficientlysmall,theDRphaseterminatesandthesolutiona

5、utomaticallyproceedstothetransientanalysisphase.Alternately,DRcanbeterminatedatapresetterminationtime.ExplicitDynamicRelaxationDRistypicallyinvokedbysettingparameterSIDRinaloadcurve(*DEFINE_CURVE)to1or2.RamptheloadduringDRphaseandthenholdloadconstantuntil

6、solutionconvergesMakesureconvergenceoccursafter100%ofpreloadisappliedMaintainthepreloadinsubsequenttransientanalysisphase(useseparateloadcurvewithouttheramp)DRconvergesSIDR=1(DRphase)SIDR=0(transientphase)*CONTROL_DYNAMIC_RELAXATION*CONTROL_DYNAMIC_RELAXA

7、TIONparametersIterationsbetweenconvergencecheck(default=250)Alsoaffectsoutputintervalfor“d3drlf”Convergencetolerance(default0.001)RatioofdistorsionalKEatconvergencetopeakdistorsionalKESmallervalueresultsinconvergedsolutionnearertosteadystatebutrunwilltake

8、longertogetthereDynamicrelaxationfactor(default=0.995)ReductionfactorfornodalvelocitieseachtimestepIfvalueistoosmall,modelneverreachsteadystateduetooverdampingOptionalterminationtimeforDR(default=infinity)DRwillstop