load determination：荷载的确定

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1、LoadDetermination:[Given]:(1)geometryoftheobjectordeviceisgiven(2)locationofthemasscenterofeachlinkisgiven(3)GiveninputforceormomentSolvingtheProblem:(1)Free-bodydiagramforeachmember(2)SetupequationsforeachmemberFor2Dproblems:---2forceequations---1momentequationFor3Dproblem

2、s:---3forceequations---3momentequationsForstaticproblems:---Sumofforces=0---Sumofmoment=0Fordynamicproblems:---Sumofforces=m*a---Sumofmoment=I*aVibrationLoading:---FiniteElementAnalysis(FEA)---BoundaryElementAnalysis(BEA)UndampedNaturalFrequency:Periodofthenaturalfrequency:

3、Tn=1/fnSpringConstant(k):Fs=k*d(forlinearspring)k=Fs¤dWhereFsºspringforcedºdeflectionofthespringDampingCoefficient(d,orC):whereDampedNaturalFrequency:(For1DOFfreeorforcedvibration)(FreeVibration)rad/sHzDynamicforces:(AvoidResonance)ImpactLoading:---thetimeofloadapplication

4、islessthanhalfoftheperiodofthenaturalfrequencyofthesystem.(Applyloadslowly---staticload)(Applyloadrapidly---impactload)(1)StrikingImpact---actualcollisionoftwobodies.(hammering)(2)ForceImpact---suddenlyappliedloadwithnovelocityofcollision.(frictionclutchesandbrakes)EnergyMe

5、thod:Elasticenergy:Treatthestruckbodyasspringeffect.Theimpactkineticenergy:(forhorizontalimpact)wherehºcorrectionfactorforenergydissipationviºimpactvelocityTherefore,Þ(dynamicforce)Staticforce:W=k*dstForverticalimpactfromaheightofh:Theimpactenergy:E=mg(hh+di)=W(hh+di)Ther

6、efore,thedynamicforceratiobecomesCorrectionFactorforaxialimpactofarodis:wherembºmassofthestruckobjectmºmassofthestrikingobject