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简介:Thedeterminationofthesoundpowerofasourceissimpleinareverberationchamber,butusuallylowervalvesareobtainedatlowfrequenciesthanthefree-spacevalue.Itisshownthatthesoundpowerdeterminedinareverberationchamberdependsnotonlyonitsfree-spacepower,butalsoonthepositionsofthesourceandthereveiver,aswellasthewaythemeasurementsaremadeandaveraged.Exactandstatisticalformulasarederivedtoaccountforthesefactors.Theresultsexplainthediscrepancyandagreewellwithearlierexperiments.Basedonthetheory,parcticabletechniquesofsoundpowerdetermina-tionarepropesedandcorrectpowerformulaspresented.
简介:Fromtheevolutionaryvectordeacriptionofslowlysime-varyingnoiseprocess,ameasurefornon-stationarityisdeveloped.Itincludesboththenon-stationaritiesofpowerandofspectrumshape.Asasingleparameter,itisacomparablequantityfordifferentprocesses.Applicationtotheanalysisofprecisegearboxisprescnted.
简介:Thesonarsystemswhichworkinshallowwaterenvironmentsuffergreatlyfrominfluencesofoceanicnoises,acousticpropagationseesawandmultipath.Withshallowwaterenvironmentandhigherrange-bearingresolutionofsonarsystems,therearenotenoughindependentscattererswithinaresolutioncellforthecentrallimittheoremtohold.Thereverberationenvelopeprobabilitydensityfunction(pdf)divergesfromRayleighpdf.Thenon-Rayleighpdfwithheaviertailsiscomplicated,anditisdifficulttoestimatethefunctionparametersaccuratelyinrealtime.WithCFAR(ConstantFalseAlarmRate)processingofthereverberationenvelopedata,whichattenuatestheheaviertailsdatavaluestotheestimatedbackgroundpowervalues,thedatareverberationistransformedfromnon-RayleighdistributiontoapproximatelyRayleighdistribution.Sinceitgetsridoftheinterferenceswhichaffecttheestimationofbackgroundpower,thedetectorcanestimatetheoceanicbackgroundpowerlevelmoreaccurately.Withtherationalestimationofbackgroundpowerlevel,theCFARdetectioncapabilityisbetterandrobust.Withprocessingofhighresolutionsonardata,itisshownthattheproposedalgorithmisefficient.
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简介:Inanon-freefield,theexistenceofdisturbingsourceswoulddestroythefree-fieldconditionrequiredbynear-fieldacousticholography,andconfusetheidentificationoftargetsourceduetothescatteringeffectcausedbydisturbingsoundfallingonthetargetsource.Tototallyremovetheinfluenceofdisturbingsource,amethodforrecoveringandreconstructingthetargetsoundfieldinanon-freefieldwasproposedbasedontheequivalentsourcemethodandthepressure-velocitymeasurement.Intheproposedmethod,thesoundfieldseparationtechniquewasfirstlyusedtoseparatethemixedsoundfieldintotheoutgoingfieldcomingfromthetargetsourceandtheincomingfieldcomingfromthedisturbingsource.Thenthescatteredcomponentcontainedintheoutgoingfieldwascalculatedbyusingthedisturbingsoundandthesurfaceimpedanceofthetargetsource.Finally,thesoundfieldradiatedbythetargetsourceinafreefieldwasobtainedbysubtractingthescatteredcomponentfromtheoutgoingfieldandwasfurtherusedtoreconstructthesoundfieldofthetargetsource.Theproposedmethodwasnumericallyandexperimentallytestifiedandtheresultsofboththesimulationandtheexperimentdemonstratedthevalidityoftheproposedmethod.
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