Sound pulse scattering from an edge of thick elastic plates:experimental and numerical investigations

I.IntroductionItisdifficulttoanaIysesoundscattcringfromanedgeofathickpIatetheoretica11y.Inmostprevious.ork['-'],thecdgcdifTractionsofidca1ha1fp1aneswereconsidered,i.e.theplanesarepcrfcct1yhardorpcrfcctlysoftoroncsurfacehardandonesurfacesoftandtheirthicknessisneg1cctcd,thccorrespondingthporicsarcquitecomp1ctc.Inthisstudy,thecdgcscattcringfromthickelasticplatesinwatcrisinvestigated.Theex'perimentalrcsultsarccxamincdphysica1lybythcp1atethcoryandcomparcdquantitative1ywithca1culationsfromanumeric…     

Overall evaluation for concert hall acoustics

I.IntroductionTherearetwowaysofcvaluatingconcertha1lacoustics.Oneistoevaluatetheacousticalqualityofaconcertha11ateachlistener'spositionrespectively,andtheotheristoevaluatetheacousticalqua1ityofaha1lasawho1e.Bothwaysarebasica1lysimilar.Howcvcr,sincesomcob-icchveparametersmayhavedifTerentvalucsatdifferentpositions,onemustdcfinesuitab1ein-dicestodescribetheseparameters(e.g.meanva1ucsorothers),sothatacomparisonbetweenha1lsbecomcspossib1e,Thispaperdea1swiththelattereva1uationbyusingfuzZysettheory…     

A study of multi-beam DICANNE system

I.IntroductionTheprob1cmofsuppressingstrongpointinterferencesourceisavcryimportantthesisinsonardesign.Fortheana1ogsonar,thesolutionofthisprob1emisquitedifficu1t.Untilthedevelopmentofdigitalsonar,thereissomerescarchreportsaboutsuppressingstrongpointin-terferencesource.Theear1ierworkin1969,dedicatcdbyV.C.Anderson,istheconccptofDICANNE(DigitalInterfcrcnceCance1lingAdaptiveNu1lNetworkEquipment)['l.Thisisadoublecompensatormulti-bcamsystcm.Oneisusedtoformintcrfercncebeamandanothcrisusedtofor…     

Study of extracting characteristic parameters from a blood vessel

I.IntroductionTheinvcrseprob1cmofsoundscattcringisinterestingtou1trasonicdiagnosis,identificationofanundcrwatcrtargct,speechsynthesisctc.UsingthismethodDucheneandTabbara[1.21.studiedtheu1trasonicdiagnosisofab1oodvessel.Inthispaperweusedasoft-tubetosimulateabloodvesselanddeaIswiththeu1trasonicdiagnosisofthesofc-tube.Invcrsescatteringprob1emdcterminingatubeparamctcrswasgivcn.Agcomctrica1acousticsmethodwasuscdindescribingthescattcrcdfield.Fivcparametcrsofthctubcwercrcconstructcd.Therelativcdc-…     

New types of complex torsional angle transformers based on hyperbolic secant taper

1.IntroductionThemaximumoutputofatransformeramplitudeislimitedbythefatigueofthema-tCrialusedlll.Ifthesurfaceshearstressofatorsionaltransformer,T,isuniformalongtheaxis,inotherwords,themaximumpointofsurfaccshearstrcssisincxistent,ti.ea1lowab1coutputpowcrofthetorsionaltransformerwillenormouslyincrease.Insomecasesinwhichveryhigh-intcnsitytorsiona1ultrasonicpowerisrequired,theywil1benecessaries.Forthispurpose,wederivedthenewtypeoftorsionalangletransformer-quartcr-wavelcngthhypcrbolicsccanttaper.T…     

Effect of wall aperture on sound propagation within a tube

I.IntroductionInmanycasesthecontinuityofsoundpropagationwithinatubeisbrokenbyaperturesonthetubewallsuchastoneholesonthemainboreofwoodwindmusicalinstruments,rectangularsound-windowofChineseinstrumentshengetc.Thediscontinuityhaseffectonwavccncoun-tCringit.Keefestudicdasing1etoneholeofwoodwindinstrumentandrepresenteditbyaT-sectionequiva1entcirc.it[11.Inthispaper,theapertureontubewa1lisstudiedfromdifferentpointofview,a1thoughtheGreen'sfunctionmethodisalsousedinthetheoreticalana1ysis.Moresimp1er…     

A beam interpolation algorithm in digital multi-beam sonar

I.IntroductionThedigita1operationins0narsystembringsagreatadvantageinbeamforming.Itispos-sib1etorealizesomcalg0rithmsindigita1technique,whichisusua11yhardtoorimpossib1etoAnp1ementintraditiona1ana1ogues0nar.Asanexamp1e,ageometrygraphofcirclearrayisil-1ustratedinFig,1.Thetotalnumber0farraye1ementisN.Therearetwokindsofbeam.TheA-c1assbeamconsistsof2M-le1ements,thesteeringdirectionisjustlocatedintheposi-honofoneofthearrayelement;TheB-classbeamconsistsof2Me1ementsandthesteeringdirectionisinthem…     

A postbeamformer adaptive noise cancelling system

I.IntroductionApostbeamformernoisecancel1erisasing1e-channeladaptiveprocessorinbeamspace['l.Ithasnotonlysimplerstructure,buta1sobetterpropertiesthane1ementspaceprocessorinimp1ementation.L.C.GodaraandA.Conto1ihavestudiedthesignaltonoiseratioofthebroadbandPIC[1].Theauthorshavesolvedtheprob1emofapplicationconditionsofnarrowbandPIC['],andproposedthatRMGSEFa1gorithmistheoptimuma1gorithminthenarrowbandPICadaptiveprocessing['1.Atpresent,thepfob1emofadaptivecance11ingofbroadbandtowing-shipnoi…     

Bulk acoustic wave Barker code sequence and the application in ultrasonic NDT

I.IntroductionUptonowtheultrasonicpu1seechotechniquehasbeenwide1yusedinthefieldofnon-destructivetesting.Toachievehightargetreso1ution,narrowpu1seshou1dbeadoptcd.Butthiswill1imitthetransmitpowerandthcdetectab1erange,whichisveryboportantcspecia1lyinthemediumwithstrongacousticattenuation.Itmeansthatthetargetresolutionanddetcctablerangehavccontradictorydcmands.Thcrcforethepulsccompressionandcorre1ationtechniqucdeve1opedinradarsystemhavebeenintroducedintotheultrasonicNDTandsomeprogresseshavebeenp…     

Theoretical analysis about eigenfrequencies of "aligned double flute

I.IntroductionFluteisanancientmusicinstrument.Itsprincipa1structureisasegmentofcircu1arpipewithaseriesofaperturesonthewa11.Amongtheseapertures,oneisca11edblowingapertureandothersarecalledtuningapertures.Duringperformance,thep1ayerb1owsbythecdgeofblowingapertureandcontro1sthetuningapertureswithcertainfingeringtoexcitedifferentpuretones.Forapopularflute,onetcrmina1ofthcfluteisopenandtheothcrisclosedwithapiston.Thetuningaperturesaresett1edneartotheopenterminalandtheblowingapertureneartotheclose…     

Parameters of microparticles responsible for the monopole sound scattering in a liquid

A monopole scattering of sound by microparticles in a liquid is considered for microparticles of two types: spherically symmetric particles similar to gas bubbles in a liquid and disk-shaped gas-filled particles whose bases may oscillate in antiphase. A transformation of the scattering amplitude to the function that, in particular, describes the oscillations of a particle removed from the liquid is proposed. This function extends the possibilities of the acoustic diagnostics of such particles. Estimates of the sound velocity in water containing disk-shaped particles suggest that the sound velocity increase observed in sea water with plankton can be explained by the monopole scattering of sound from a single plankton particle modeled as a rigid gas-filled disk with oscillating parts of its bases.     

浅海温跃层声散射实验研究

本文给出１９８８、１９８９和１９９２年夏季南黄海海域三站位（水深３４米、４４米和３９米）处的温跃层声脉冲反向散射实验结果。实验用窄带脉冲声源的中心频率分别为１２０ｋＨｚ、１６０ｋＨｚ和２００ｋＨｚ。实验过程中同时用ＣＴＤ仪昼夜分段记录温、盐、深参数和分层拖网采集浮游生物样本。作者根据Ｒ．Ｋｉｎｄ关于平面波在任意分布不均匀层系上反射系数谱的计算方法，求出以实测温、盐垂直分布构成的不均匀层系上反射系数谱，得到跃层散射在时域上的数值模拟散射信号，与海上实测记录在时域和幅度进行对比。三年同期重复实验结果表明：实测跃层散射波到达接收点的时间与按温度剖面所做数值模拟计算结果相符。浮游生物样品分析数据与声信号记录看不出确定的对应关系，说明声散射主要是海水介质的物理不均匀性引起。     

An experimental study of acoustic scattering from thermocline in shallow sea

I.IntroductionThetemperature,salinityandstaticprcssureofscawaterchangewithdepth,whichformsthcsoundvelocityvertica1distributioninthesea.Duringsummcrscason,thercaren0n-uniformthermoclinelaycrsinthedepths0fshallowseaal0ngChinacoast.Wearenowabletodeducctheimpedanccproflle(pc)byechoesofacousticwavesfr0mvarioustherm0c1ine1ayers.Thewaterdcnsityvaricsonlyslight1y,hencetheac0usticve1ocityde-Pendsmainlyonthetemperatureofseawatcr,andthercfore,itispossiblctorecordthcdepthofthermoclinelaycrsbyusingacoust…     

开口/封闭薄壳体声辐射和散射的统一边界积分方程解法

推导了在二维和三维空间下开口和封闭薄壳体在任意阻抗边界条件下声辐射和散射的统一边界积分方程.相对于以前的求解方法,该方程求解声辐射和散射问题具有相同的影响矩阵,能够同时求解薄壳体气动和振动噪声的辐射和散射现象,以及分析壳体声阻抗对声波传播的影响.推导的方程可以应用于叶轮机械、管道等噪声和消声器消声性能的预测等方面.在此方程基础上,可以进一步考虑运动边界和运动介质对声辐射和散射的影响. 关键词： 薄壳体 声阻抗 积分方程 边界元方法     

Research on the acoustic scattering function and coherence properties from rough seafloor based on finite element model

Acoustic scattering from a rough sea bottom is recognized as a main source of reverberation. In this study, scattering properties from a layered bottom were exploited based on the finite element model. The scattering strength and loss from the layered rough seabed were investigated by ensembling the realizations of rough interface. They were found to be dependent on the thickness of sediment, and interference was significant in the case of thin sediment. Through verification of the finite element model, the scattering loss could be evaluated using the Eckart model with a proper sound speed in the thick sediment. The multiple scattering effect on the sound field was also exploited. It revealed that the effect depended strongly on the bottom type.     

Bubble nonlinear dynamics and stimulated scattering process

A complete understanding of the bubble dynamics is deemed necessary in order to achieve their full potential applications in industry and medicine. For this purpose it is first needed to expand our knowledge of a single bubble behavior under different possible conditions including the frequency and pressure variations of the sound field. In addition, stimulated scattering of sound on a bubble is a special effect in sound field, and its characteristics are associated with bubble oscillation mode. A bubble in liquid can be considered as a representative example of nonlinear dynamical system theory with its resonance, and its dynamics characteristics can be described by the Keller–Miksis equation. The nonlinear dynamics of an acoustically excited gas bubble in water is investigated by using theoretical and numerical analysis methods. Our results show its strongly nonlinear behavior with respect to the pressure amplitude and excitation frequency as the control parameters, and give an intuitive insight into stimulated sound scattering on a bubble. It is seen that the stimulated sound scattering is different from common dynamical behaviors, such as bifurcation and chaos, which is the result of the nonlinear resonance of a bubble under the excitation of a high amplitude acoustic sound wave essentially. The numerical analysis results show that the threshold of stimulated sound scattering is smaller than those of bifurcation and chaos in the common condition.     

Active control of radiation from a piston set in a rigid sphere

Active control of the sound radiated from a piston set in a rigid sphere with a set of control point sources around is considered in this paper, where the scattering sound field of the control sound from the rigid sphere has been taken into account to minimize the total radiated sound power. Analytic results of the sound power are obtained and numerical simulations show that it is possible to reduce the radiation from a small piston set in a rigid sphere similar to the size of a human head up to a certain frequency. It is found that the introduction of the scattering object makes significant differences from the active control without scattering objects. This being the case, the scattering object makes the active noise control easier. To increase the global reduction of sound-power output, the optimal number and locations of the control sources and the optimal number and locations of error sensors are discussed. Finally, experiments with one control source and one error sensor around a head simulator have been carried out to verify the simulation results.     

Modification to first-order Born approximation for improved prediction of scattered sound from weakly scattering objects

When deriving the Fourier diffraction theorem based on the first-order Born approximation,the difference between wave number of the scattering object and that of the surrounding medium is ignored,causing substantial errors in sound scattering prediction.This paper modifies the Born approximation by taking into account the amplitude and phase changes between the scattering object and the water due to the wave number difference.By changing the radius and center position of the sampling circle in the Fourier domain,accuracy of the predicted sound scattering is improved.With the modified Born approximation,the computed far-field directional pattern of the scattered sound from a circular cylinder is in good agreement with the rigorous solution.Numerical calculations for several objects with different shapes are used to show applicability and effectiveness of the proposed method.     

Measurements of bubbles in sea water by nonstationary sound scattering

Methods for the characterization of bubbles in sea water by acoustic scattering are analyzed. Nonstationary linear and nonlinear sound scattering methods are proposed. The transient linear and nonlinear sound scattering allows the scattering by resonant gas bubbles to be distinguished from the scattering by other microinhomogeneities. The application of parametric arrays in oceanic experiments, together with the broadband frequency analysis of the backscattering coefficient, allows information about bubbles in sea water to be obtained. Experimental results on sound scattering and gas bubble distribution functions are presented for different conditions in the ocean.     

平面波与平面行波脉冲的声相互作用

Westervelt在研究两正交平面波的相互作用时曾经推论:在两个波的公共区之外没有散射声。但由于所论的公共区不是一个有限大的区域,故“公共区之外”是没有实际意义的。本文讨论一列平面波与一列平面行波脉冲的声相互作用,显然这两个波不仅都满足波动方程,而且可以用来讨论公共区之外的声散射声问题。计算结果表明,如果介质没有频散效应,则公共区之外不存在服从因果律的声散射声。本文还指出,对于这两个一阶场所构成的公共区来说,应用Lighthill远场积分来讨论这种情况下的声散射声是不妥当的。 关键词：