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1、ARTICLEINPRESSMechanicalSystemsandSignalProcessingMechanicalSystemsandSignalProcessing22(2008)1107–1132www.elsevier.com/locate/jnlabr/ymsspDetectionandidentificationofnonlinearitiesbyamplitudeandfrequencymodulationanalysisa,bP.FrankPai,AnthonyN.PalazottoaD
2、epartmentofMechanicalandAerospaceEngineering,UniversityofMissouri-Columbia,Columbia,MO65211,USAbDepartmentofAeronauticsandAstronautics,AirForceInstituteofTechnology,Wright-PattersonAirForceBase,OH45433,USAReceived10August2007;receivedinrevisedform18October
3、2007;accepted7November2007Availableonline17November2007AbstractThispaperpresentsanamplitudeandfrequencymodulationmethod(AFMM)forextractingcharacteristicsofnonlinearsystemsandintermittenttransientresponsesbyprocessingstationary/transientresponsesusingtheemp
4、iricalmodedecomposition,Hilbert–Huangtransform(HHT),andnonlineardynamiccharacteristicsderivedfromperturbationanalysis.Asliding-windowfitting(SWF)methodisderivedandusedtoshowthephysicalimplicationsoftheproposedmethodandothermethodsfordataprocessingandtransfo
5、rmation.Similartothewavelettransform,theSWFuseswindowedregularharmonicsandfunctionorthogonalitytoextracttime-localizedregularand/ordistortedharmonics,andthentheamplitudeandfrequencymodulationsoftheharmonicsareusedtoidentifysystemnonlinearities.Ontheotherha
6、nd,theHHTusestheapparenttimescalesrevealedbythesignal’slocalmaximaandminimaandcubicsplinesoftheextrematosequentiallysiftcomponentsofdifferenttimescales,startingfromhigh-frequencytolow-frequencyones.BecauseHHTdoesnotusepredeterminedbasisfunctionsandfunction
7、orthogonalityforcomponentextraction,itprovidesmoreaccurateinstantamplitudesandfrequenciesofextractedcomponentsforaccurateestimationofsystemcharacteristicsandnonlinearities.Moreover,becausethefirstcomponentextractedbyHHTcontainsalloriginaldiscontinuities,its
8、time-varyingamplitudeandfrequencyareexcellentindicatorsforpinpointingtimesandlocationsofimpulsiveexternalloads.However,thediscontinuity-inducedGibbs’phenomenonmakesHHTanalysisinaccuratearoundthetwodataends.On
