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8.1.UnderstandingRotatingStructureDynamicsYoucanobserveinertiaeffects,appliedviatheCORIOLIScommand,ineitherastationaryreferenceframeorarotatingreferenceframe.Inbothcases,youspecifyangularvelocitybyissuinganOMEGAorCMOMEGAcommand.Thedynamicequationincorporatingtheeffectofrotationisgivenbywhere[M],[C]and[K]arethestructuralmass,damping,andstiffnessmatrices,respectively.[Kc]isthespinsofteningmatrix(describedinSpinSofteningintheTheoryReferenceforANSYSandANSYSWorkbench.)[G]isa“damping”matrixcontributionduetotherotationofthestructurespecifiedviatheOMEGAorCMOMEGAcommand(describedinRotatingStructuresintheTheoryReferenceforANSYSandANSYSWorkbench).WithouttheinertiaeffectappliedviatheCORIOLIScommand,ANSYSdoesnotgeneratethe[G]matrix,andtheusualeffectoftheangularrotationvelocityspecifiedbytheOMEGAorCMOMEGAcommandapplies(asdescribedinAccelerationEffectintheTheoryReferenceforANSYSandANSYSWorkbench).Anexceptionexists,however,involvinganonlineartransientanalysisusingelementsMASS21,BEAM188,andBEAM189;inthiscase,theinertiaeffectduetorotationappliedviaanICcommand(oraDcommandoveranincrementaltime)isincludedwithouthavingtoissueCORIOLISandOMEGAorCMOMEGAcommands8.2.UsingaStationaryReferenceFrameTheprimaryapplicationforastationary(ratherthanarotating)frameofreferenceisinthefieldofrotordynamicswherearotatingstructure(rotor)ismodeledalongwithastationarysupportstructure.Examplesofsuchanapplicationincludeagasturbineenginerotor-statorassemblyoranelectricturbogenerator,wheretherotorspinsinsideaspeciallydesignedhousing.Therotatingpartofthestructuretobemodeledmustbeaxisymmetric.Thegyroscopicdampingmatrixgeneratedisvalidonlyforalinearanalysis.ANSYScomputesthedisplacementfieldwithrespecttotheglobalcoordinatesystem(CORIOLIS,Option=ON,,,RefFrame=ON),referredtoasthestationaryreferenceframe.ElementsSupportedElementsthatarepartoftherotatingstructuregeneratethegyroscopicmatrixthatarisesduetotherotationalangularvelocity.Thegyroscopicmatrixisavailableforthefollowingelements:BEAM4,PIPE16,MASS21,SOLID45,SOLID95,SOLID185,SOLID186,SOLID187,BEAM188,andBEAM189.Forabeamelement,theangularvelocityvectorisalignedalongthelengthandthepointmassisalignedalongoneoftheprincipalaxes.Therotatingstructuremustbeaxisymmetricaboutthespinaxis.AnalysisTypesSupportedThefollowinganalysistypessupportrotatingstructureanalysisusingastationaryreferenceframe:Modal(ANTYPE,MODAL)Transient(ANTYPE,TRANS)Harmonic(ANTYPE,HARMIC)--Fortransientandharmonicanalyses,thefull(TRNOPT,FULL)andmode-superposition(TRNOPT,MSUP)methodsaresupported.Forthemode-superpositionmethod,onlytheQRDampmode-extractionmethod(MODOPT,QRDAMP)issupported.Toincludeunbalanceorgeneralasynchronousrotatingforcesinaharmonicanalysis,usetheSYNCHROcommand.Foratransientanalysisinvolvingarotatingstructurewithastationaryreferenceframe,supportforastartorstopsimulationisavailable.IssuetheKBCcommandtoramptherotationalvelocity.Foraprestressedanalysisthatincludesgyroscopiceffects,issuetheCORIOLIS,ON,,,ONcommandinthestaticprestressportionoftheanalysis.PostprocessingBesidesgeneralresults,thefollowingspecificoutputsareavailable:Campbelldiagram(PRCAMPandPLCAMP)see8.2.1NoteForaprestressedstructure,settheCampbellkey(CAMPBELL,ON)inthefirstsolutionpass.DoingsoallowsaCampbelldiagramanalysis.Orbits(PRORBandPLORB)see8.2.3Animationofthewhirl(ANHARM)8.2.1.CampbellDiagramInamodalanalysiswithmultipleloadstepscorrespondingtodifferentangularvelocitiesω,aCampbelldiagram(PLCAMPorPRCAMP)showstheevolutionofthenaturalfrequencies.ANSYSdetermineseigenfrequenciesateachloadstep.Theplotshowingthevariationofeigenfrequencywithrespecttorotationalspeedmaynotbereadilyapparent.Forexample,ifthegyroscopiceffectissignificantonaneigenmode,itsfrequencytendstosplitsomuchthatitcrossestheotherfrequencycurvesasthespeedincreases.Formoreinformation,seeGeneratingaSuccessfulCampbellDiagrambelow.CriticalSpeedsThePRCAMPcommandalsoprintsoutthecriticalspeedsforarotatingsynchronous(unbalanced)orasynchronousforce.ThecriticalspeedscorrespondtotheintersectionpointsbetweenfrequencycurvesandtheaddedlineF=s.ω(wheresrepresentsSLOPE0asspecifiedviaPRCAMP).Becausethecriticalspeedsaredeterminedgraphically,theiraccuracydependsuponthequalityoftheCampbelldiagram.Toretrieveandstorecriticalspeedsasparameters,usethe*GETcommand.WhirlsandStabilityAseigenfrequenciessplitwithincreasingspinvelocity,ANSYSidentifiesforward(FW)andbackward(BW)whirls,andunstablefrequencies.Toobtainmoreinformationtohelpyoudeterminehowaparticularfrequencybecomesunstable,issuethePLCAMPorPRCAMPcommandandspecifyastabilityvalue(STABVAL)of1.YoucanalsoviewthelogarithmicdecrementsbyspecifyingSTABVAL=2.Formoreinformationaboutcomplexeigenvaluesandcorrespondinglogarithmicdecrements,seeDampedMethodintheTheoryReferenceforANSYSandANSYSWorkbench.Toretrieveandstorefrequenciesandwhirlsasparameters,usethe*GETcommand.PrestressedStructureForaprestressedstructure,settheCampbellkey(CAMPBELL,ON)inthestaticsolutionportionoftheanalysis.DoingsomodifiestheresultfilesothatitcanaccommodateasubsequentCampbelldiagramanalysis.Inthiscase,staticandmodalso