PreloadsinLS DYNA IntroductionAnalysisTechniques General DynamicRelaxationExplicitImplicitTransientExplicitwithMassDampingImplicitAnalysisBoltPreloadTechniquesThermalInterferenceContactStressinSolidCross sectionForceinBeams Preload Introduction Sometimesitisimportanttoinduceasteadystatepreloadbeforeperformingatransientdynamicanalysis Rotatingfanorturbineblades rotatingflywheelsGravityPressurevesselsortiresShrink fitpartsStressesinducedbyatorquedbolt ExplicitDynamicRelaxation DR ExplicitDRisanoptionaltransientanalysisthattakesplacein pseudo 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 willinvokeacompletelydifferentandfasterinitializationapproach InitializationbyPrescribedGeometry Requiressupplementalinputfilecontainingnodaldisplacementsandrotations m filename onexecutionline Suchafiledrdisp sifiswrittenatconclusionofstandardDRrun Ifnodalrotationsarenotincludedinfile methodisinvalidforbeamsandshells LS DYNA runsashorttransientanalysisof100timestepstopreloadthemodelbyimposingthenodaldisplacementsandrotations 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 PrePost allowsusertoconfirmsolutionisnearsteadystaterelaxfileisautomaticallywrittenandcontainsrecordofconvergencehistory 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 Example GravityLoadingonaTire g Contact Groundisconstrained OneofthetiresfromNCAC sFord250wasusedinthisexamplebutwithoutthecontrolvolume 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