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1、PreloadsinLS DYNA IntroductionAnalysisTechniques General DynamicRelaxationExplicitImplicitTransientExplicitwithMassDampingImplicitAnalysisBoltPreloadTechniquesThermalInterferenceContactStressinSolidCross sectionForceinBeams Preload Introduction Sometimesitisimportanttoinduceasteadystatepreloadbefore
2、performingatransientdynamicanalysis Rotatingfanorturbineblades rotatingflywheelsGravityPressurevesselsortiresShrink fitpartsStressesinducedbyatorquedbolt ExplicitDynamicRelaxation DR ExplicitDRisanoptionaltransientanalysisthattakesplacein pseudo time precedesregulartransientanalysis DRistypicallyuse
3、dtopreloadamodelbeforeonsetoftransientloading Preloadstressesaretypicallyelasticanddisplacementsaresmall InexplicitDR thecomputednodalvelocitiesarereducedeachtimestepbythedynamicrelaxationfactor default 995 ThusthesolutionundergoesaformofdampingduringDR Thedistortionalkineticenergyismonitored Whenth
4、isKEhasbeensufficientlyreduced i e the convergencefactor hasbecomesufficientlysmall theDRphaseterminatesandthesolutionautomaticallyproceedstothetransientanalysisphase Alternately DRcanbeterminatedatapresetterminationtime ExplicitDynamicRelaxation DRistypicallyinvokedbysettingparameterSIDRinaloadcurv
5、e DEFINE CURVE to1or2 RamptheloadduringDRphaseandthenholdloadconstantuntilsolutionconvergesMakesureconvergenceoccursafter100 ofpreloadisappliedMaintainthepreloadinsubsequenttransientanalysisphase useseparateloadcurvewithouttheramp CONTROL DYNAMIC RELAXATION CONTROL DYNAMIC RELAXATIONparametersIterat
6、ionsbetweenconvergencecheck default 250 Alsoaffectsoutputintervalfor d3drlf Convergencetolerance default0 001 RatioofdistorsionalKEatconvergencetopeakdistorsionalKESmallervalueresultsinconvergedsolutionnearertosteadystatebutrunwilltakelongertogetthereDynamicrelaxationfactor default 0 995 Reductionfa
7、ctorfornodalvelocitieseachtimestepIfvalueistoosmall modelneverreachsteadystateduetooverdampingOptionalterminationtimeforDR default infinity DRwillstopiftimereachesDRTERMevenifconvergencecriterionnotsatisfiedTimestepscalefactorusedduringDR ExplicitDynamicRelaxation CONTROL DYNAMIC RELAXATIONparameter
8、sIDRFLGFlagtoactivateDR notrequiredifDRisactivatedwith DEFINE CURVE Setto2 willinvokeacompletelydifferentandfasterinitializationapproach InitializationbyPrescribedGeometry Requiressupplementalinputfilecontainingnodaldisplacementsandrotations m filename onexecutionline Suchafiledrdisp sifiswrittenatc
9、onclusionofstandardDRrun Ifnodalrotationsarenotincludedinfile methodisinvalidforbeamsandshells LS DYNA runsashorttransientanalysisof100timestepstopreloadthemodelbyimposingthenodaldisplacementsandrotations Solutionthenproceedswithregulartransientanalysis Setto5 activatesimplicitmethodforsolutionofpre
10、loadedstateMustalsosetDRTERMtosignalendofDRphase CONTROL IMPLICIT providecontrolsonimplicitphase CONTROL DYNAMIC RELAXATION DynamicRelaxation OutputRelatedtoDynamicRelaxation ASCIIoutputfilesareNOTwrittenduringDRphase e g glstat matsum rcforc etc Thebinaryd3thdtfilecanbeusedifIDRFLG 1 Binarydatabase
11、 d3drlf iswrittenbyincludingcommand DATABASE BINARY D3DRLF Setoutputintervalto1 ThiswillcauseastatetobewritteneachtimeconvergenceischeckedduringDRPlottingtimehistoriesfromd3drlfwithLS PrePost allowsusertoconfirmsolutionisnearsteadystaterelaxfileisautomaticallywrittenandcontainsrecordofconvergencehis
12、tory DatacanbeplottedwithLS PrePost drdisp sifcontainsnodaldisplacementsandrotationsatconclusionofDRphase DynamicRelaxation OutputRelatedtoExplicitDynamicRelaxation ExplicitDynamicRelaxation DynamicRelaxationinformationiswrittentothescreen ThetransientphasestartswhentheconvergencetoleranceoraSpecifi
13、edterminationtimeisreached Convergenceplotfromrelaxfile KineticEnergyplotfromrelaxfile TypicalLoadsDuringDynamicRelaxation Gravityloadsandcentrifugalloads spinningbodies areimposedusing LOAD BODY option LCIDandLCIDDRareseparatecurvesfortransientphaseandDRphase respectively Thermalstressescanbeimpose
14、dusing LOAD THERMAL LOAD CURVE Parts e g bolts definedwithacoefficientofthermalexpansionwillhavethermalstressesimposed LCIDandLCIDDRareseparatecurvesfortransientphaseandDRphase respectively OtherloadtypesorboundaryconditionsareappliedduringDRifSIDRincorresponding DEFINE CURVEissetto1or2 Example LOAD
15、 SEGMENT BOUNDARY PRESCRIBED MOTION CONTACT INTERFERENCEimposesloadassociatedwithgeometricinterference INITIAL moreonthatlater DynamicRelaxation ExplicitDynamicRelaxation Example GravityLoadingonaTire g Contact Groundisconstrained OneofthetiresfromNCAC sFord250wasusedinthisexamplebutwithoutthecontro
16、lvolume Agravityloadisappliedinthetransientphaseasaconstantcurve whichmakesthetirebounceduringthesimulation time 1 asseenwhenplottingtheZ displacementforanodeonthetirerim ThismodelisusedtoinvestigatethebehaviorofDynamicRelaxation NodeConsidered DynamicRelaxation Example GravityLoadingonaTire DynamicRelaxationwasaddedtothemodelusingarampedloadcurvefortheDRphase i e loadcurveLCIDDR LOAD BODY Z hasSIDR DEFINE CURVE setto1 TheloadisrampedincurveLCIDDRover2000timesteps The CONTROL DYNAMIC RELAXATIONp
