简介：Thenumericalquadraturemethodsfordealingwiththeproblemsofsingularandnear-singularintegralscausedbyBurton-Millermethodareproposed,bywhichtheconventionalandfastmultipoleBEMs(boundaryelementmethods)for3Dacousticproblemsbasedonconstantelementsareimproved.Tosolvetheproblemofsingularintegrals,aHadamardfinite-partintegralmethodispresented,whichisasimplifiedcombinationofthemethodsproposedbyKirkupandWolf.Theproblemofnear-singularintegralsisovercomebythesimplemethodofpolartransformationandthemorecomplexmethodofPART(ProjectionandAngular&RadialTransformation).Theeffectivenessofthesemethodsforsolvingthesingularandnear-singularproblemsisvalidatedthroughcomparingwiththeresultscomputedbytheanalyticalmethodand/orthecommercialsoftwareLMSVirtual.Lab.Inaddition,theinfluenceofthenear-singularintegralproblemonthecomputationalprecisionsisanalyzedbycomputingtheerrorsrelativetotheexactsolution.ThecomputationalcomplexitiesoftheconventionalandfastmultipoleBEMareanalyzedandcomparedthroughnumericalcomputations.Alarge-scaleacousticscatteringproblem,whosedegreeoffreedomsisabout340,000,isimplementedsuccessfully.Theresultsshowthat,thenearsingularityisprimarilyintroducedbythehyper-singularkernel,andhasgreatinfluencesontheprecisionofthesolution.TheprecisionoffastmultipoleBEMisthesameasconventionalBEM,butthecomputationalcomplexitiesaremuchlower.

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简介：Usingtheextremedifferenceofself-similarityandkurtosisatlargelevelscaleofwavelettransformapproximationbetweenthePTFM(PulseTrainsofFrequencyModulated)signalsanditsreverberation,afeature-basedmatchedfiltermethodusingtheclassify-before-detectparagriamisproposedtoimprovethedetectionperformanceinreverberationandmultipathenvironments.Processingthedataoflake-trailsshowedthattheprocessinggainoftheproposedmethodisbiggerthanthatofmatchedfilterabout10dB.Inmultipathenvironments,detectionperformanceofmatchedfilterbecomebadlypoorer,whilethatoftheproposedmethodisimprovedbetter.Itshowsthatthemethodismuchmorerobustwiththeeffectofmultipath.

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简介：Thisstudyperformsthequantitativeanalysisandcomparisontoacousticsignalcharact,eristicsofLargcyellowcroaker(Pseudosciaenacrocea)attwodifferentages.Thesoundswercrecordedfromthefishesinanet-cage.Twoexponentialoscillationfunctionsarebuilttofittheacousticsignalofthefishes.Thesignalcharacteristicoftheoscillationfrequencyandattcnuationcoefficientwasdescribedquantitatively.Simulationcurvesofthefunctioncouldfitwellacousticsignals.Boththeaverageoscillationfrequencyandattenuationcoefficientofthefittedsignalsfromthe13-15-month-oldfishesarclowerthanthosefromthe7-8-month-oldfishes.Theresultssuggestthattheoscillationfrequencyandattenuationcoefficientoftheacollsi.icsignalfunctionmayberelevanttothephysicalproccssofsoundproductionandagecharacteristicsofLargeyellowcroaker.Thisstudymaybevaluablefortheacousticapplicationtotheartificialcultureofthespecies.