教程5.13g加密所属-msc

SECTION9DAMPINGOVERVIEWTABLEOFCONTENTS

PageDAMPINGINDYNAMICANALYSIS 9-3RAYLEIGHDAMPING 9-7VISCOUSDAMPINGINPUT 9-9FREQUENCYDEPENDENTIMPEDANCESAMPLE 9-24SAMPLEUSINGCBUSHELEMENT 9-25DISPLACEMENTOUTPUTFORCBUSHELEMENT 9-26FORCEOUTPUTFORCBUSHELEMENT 9-27DAMPINGINDYNAMICANALYSISSection2includedanoverviewofthebasicdampingtheoryviaSDOFand2DOFmodelsSections10and11includedetailsofimplementationofmaterialdampinginTransientandFrequencyResponseAnalysisThissectionprovidesareviewofthedamping‘elements’availableinNastrananddiscusseswhatphysicallyproducesdampingDAMPINGINDYNAMICANALYSISDampingispresentinalloscillatorysystemsDampingremovesenergyfromasystemPossibleenergydissipationvia:HeatSoundwavesFluidmotionResultingeffect:FreeVibrationgivesdecayinamplitudeSteadyStategivesenergyloss=energyinputMechanismsinclude:InternalMolecularfriction-rawmaterialSlidingFriction-joints,pliesFluidResistance-dampers,airorwaterenvironmentDAMPINGINDYNAMICANALYSIS(Cont.)WhatlevelsofdampingshouldIuse?Thereisnoonegoodanswertothisquestion!Foraparticularstructuralconfigurationandmateriallookat:TestresultsIndustrystandards

Companyexperience

RememberinGenerallowestlevelsofdampingaremostconservative:Usearangeofdampingvaluesinpresentingresults

Peakresponseisdifficulttocapture

Typicalvalues(NOTTOBEQUOTED!):NCmachinedcomponents–2%to5%criticalFabricatedmetalcomponents–4%to10%critical

Composites–6%to20%critical

DAMPINGINDYNAMICANALYSIS(Cont.)DampingtypesinNASTRAN:

Viscous–dampingforceisproportionaltovelocity(i.e.frequencydependent)TypicalDashpotbehavior

Structural–dampingforceisproportionaltodisplacementTypicalSteelorAluminumbehaviorRayleighdamping–dampingforceisproportionaltoStiffnessand/orMassArealstructurecouldhaveanycombinationofthesetypesRAYLEIGHDAMPINGNotSupportedinPatran,requiresDirectTextInputProportionaltoeitherthemassorstiffnessmatrixAlsoknownasproportionaldampingProportionaltomassmatrix(param,alpha1,x)Proportionaltostiffnessmatrix(param,alpha2,y)AvailableintransientandfrequencyresponseanalysisScalefactorsappliedtod-set(direct)andh-set(modal)Addedtotheviscousdampingmatrixasfollows:[B’]=[B]+alpha1*[M]+alpha2*[K]RAYLEIGHDAMPING(Cont.)

ALPHA1andALPHA2arecomplexparameters,e.g.PARAM,ALPHA2,1.25E-4,0.ModalDampingMatrixreadsVISCOUSDAMPINGINPUTScalarviscousdampingCDAMP1 ScalardamperbetweentwoDOFswithreferencetoapropertyentryCVISC Elementdamperbetweentwogridpoints;referencesapropertyentry(PVISC)CBUSHGeneralizedSpringandDamperelementthatmaybedefinedasFrequencyDependent.DampingvaluesareassignedviaPhysicalPropertyinputonaPBUSHentryVISCOUSDAMPINGINPUT(Cont.)ScalardampingCDAMP1ElementTherearetwoformsGroundedDamper–onlyonegridisconnectedScalarDamper–bothgridsareconnectedCDAMP1(Grounded)ElementCDAMP1ElementVISCOUSDAMPINGINPUT(Cont.)VISCOUSDAMPINGINPUT(Cont.)VISCOUSDAMPINGINPUT(Cont.)ViscousdampingCVISCElementCVISCElementVISCOUSDAMPINGINPUT(Cont.)VISCOUSDAMPINGINPUT(Cont.)VISCOUSDAMPINGINPUT(Cont.)CBUSHElementVISCOUSDAMPINGINPUT(Cont.)VISCOUSDAMPINGINPUT(Cont.)VISCOUSDAMPINGINPUT(Cont.)VISCOUSDAMPINGINPUT(Cont.)VISCOUSDAMPINGINPUT(Cont.)VISCOUSDAMPINGINPUT(Cont.)VISCOUSDAMPINGINPUT(Cont.)FREQUENCYDEPENDENTIMPEDANCESAMPLESAMPLEUSINGCBUSHELEMENT$$ cbush1.dat$TIME10SOL108CENDTITLE=VERIFICATIONPROBLEM,FREQ.DEP.IMPEDANCEBUSHVERSUBTITLE=SINGLEDOF,CRITICALDAMPING,3EXCITATIONFREQUENCIESECHO=BOTHSPC=1002DLOAD=1DISP=ALLFREQ=10ELFO=ALLBEGINBULK$CONVENTIONALINPUTFORMOUNTGRDSET, , , , , , , 23456$PS$TIEDOWNEVERYTHINGBUTTHE1DOFGRID, 11, , 0., 0., 0.0 $GROUND=, 12, =, =, =, , $ISOLATEDDOFSPC1, 1002 123456 11 $GROUNDCONM2, 12, 12, , 1.0 $THEISOLATEDMASS$$ EID PID GA GB GO/X1 X2 X3 CID$CBUSH 1000 2000 11 12 0$PBUSH 2000 K 1.0 B 0.0$PBUSHT 2000 K 2001 B 2002$TABLED1,2001$STIFFNESSTABLE, 0.9 0.81, 1.0, 1.0, 1.1, 1.21 ENDTTABLED12002$DAMPINGTABLE, 0.9 .2864789,1.0, .318309,1.1 , .3501409ENDT$CONVENTIONALINPUTFORFREQUENCYRESPONSEPARAM, WTMASS, .0253303$1/(2*PI)**2.GIVESFN=1.0DAREA, 1, 12, 1, 2.$CAUSESUNITDEFLECTIONFREQ, 10, 0.9, 1.0, 1.1$BRACKETTHENATURALFREQUENCYRLOAD1, 1, 1, , , 3TABLED1,3$TABLEFORFORCEVS.FREQUENCY, 0.9, 0.81, 1., 1., 1.1, 1.21,ENDT$P=KENDDATADISPLACEMENTOUTPUTFORCBUSHELEMENTFREQUENCY=9.000000E-01 COMPLEXDISPLACEMENT (REAL/IMAGINARY) POINTID. TYPE T1 T2 T3 R1 R2 R30 11 G .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .00 12 G -6.682744E-08 .0 .0 .0 .0 .0 -1.000000E+00 .0 .0 .0 .0 .01 VERIFICATIONPROBLEM,FREQ.DEP.IMPEDANCE BUSHVER MARCH20,1997MSC.Nastran1/23/97PAGE8 SINGLEDOF,CRITICALDAMPING,3EXCITATIONFREQUENCIES0FREQUENCY=1.000000E+00 COMPLEXDISPLACEMENT (REAL/IMAGINARY) POINTID. TYPE T1 T2 T3 R1 R2 R30 11 G .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .00 12 G -1.046835E-07 .0 .0 .0 .0 .0 -9.999999E-01 .0 .0 .0 .0 .01 VERIFICATIONPROBLEM,FREQ.DEP.IMPEDANCE BUSHVER MARCH20,1997MSC.Nastran1/23/97PAGE9 SINGLEDOF,CRITICALDAMPING,3EXCITATIONFREQUENCIES0FREQUENCY=1.100000E+00 COMPLEXDISPLACEMENT (REAL/IMAGINARY) POINTID. TYPE T1 T2 T3 R1 R2 R30 11 G .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .00 12 G -6.855670E-08 .0 .0 .0 .0 .0 -9.999999E-01 .0 .0 .0 .0 .01 VERIFICATIONPROBLEM,FREQ.DEP.IMPEDANCE BUSHVER MARCH20,1997MSC.Nastran1/23/97PAGE10 SINGLEDOF,CRITICALDAMPING,3EXCITATIONFREQUENCIESFORCEOUTPUTFORCBUSHELEMENTFREQUENCY=9.000000E-01 COMPLEXFORCESINBUSHELEMENTS(CBUSH) (REAL/IMAGINARY) ELEMENT-ID. FORCE-X FORCE-Y FORCE-Z MOMENT-X MOMENT-Y MOMENT-Z0 1000 1.620000E+00 .0 .0 .0 .0 .0 -8.100000E-01 .0 .0 .0 .0 .01 VERIFICATIONPROBLEM,FREQ.DEP.IMPEDANCE BUSHVER MARCH20,1997MSC.Nastran1/23/97PAGE11 SINGLEDOF,CRITICALDAMPING,3EXCITATIONFREQUENCIES0FREQUENCY=1.000000E+00 COMPLEXFORCESINBUSHELEMENTS(CBUS