Ray chaos and ray clustering in an ocean waveguide

We consider ray propagation in a waveguide with a designed sound-speed profile perturbed by a range-dependent perturbation caused by internal waves in deep ocean environments. The Hamiltonian formalism in terms of the action and angle variables is applied to study nonlinear ray dynamics with two sound-channel models and three perturbation models: a single-mode perturbation, a randomlike sound-speed fluctuations, and a mixed perturbation. In the integrable limit without any perturbation, we derive analytical expressions for ray arrival times and timefronts at a given range, the main measurable characteristics in field experiments in the ocean. In the presence of a single-mode perturbation, ray chaos is shown to arise as a result of overlapping nonlinear ray-medium resonances. Poincare maps, plots of variations of the action per ray cycle length, and plots with rays escaping the channel reveal inhomogeneous structure of the underlying phase space with remarkable zones of stability where stable coherent ray clusters may be formed. We demonstrate the possibility of determining the wavelength of the perturbation mode from the arrival time distribution under conditions of ray chaos. It is surprising that coherent ray clusters, consisting of fans of rays which propagate over long ranges with close dynamical characteristics, can survive under a randomlike multiplicative perturbation modelling sound-speed fluctuations caused by a wide spectrum of internal waves.     

Wave analysis of ray chaos in underwater acoustics

The dispersion of a wave packet in an acoustic medium is considered in the paraxial wave approximation, where the effective potential, due to variation of the speed of propagation, varies both with depth and propagation distance. The analysis of the resulting parabolic equation, similar to the Schrodinger equation, clearly demonstrates the role of ray chaos in enhancing the dispersion of the initial packet. However, wave coherence effects are also seen that suppress the effects of the ray chaos in a manner analogous to the effects of quantum chaos. (c) 1999 American Institute of Physics.     

Interrelation between ray and mode field representations in an acoustic waveguide

Some well-known results obtained by Brekhovskikh, Felsen, Tindle, Guthrie, and other authors during their studies of the interrelation between modes and rays in a plane-layered waveguide are briefly discussed. The relationships that extend these results to the case of a waveguide with large-scale inhomogeneities of the refractive index are analyzed. It is shown that in the presence of inhomogeneities, the groups of the constructively interfering modes, as in the case of a plane-layered waveguide, also form contributions of individual rays. In this case, fluctuations of the amplitudes of normal modes can be described by simple ray formulas, which are the mode analogs of the relationships of geometric optics and the smooth perturbation method.Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 1–2, pp. 115–121, January–February, 1995.     

水声波导中包络线谱强度数值预报

为了预报声呐远距离检测包络线谱的性能,本文分析在辐射噪声传播过程中包络线谱强度衰减的原因及提出在水声波导中包络线谱强度的数值预报方法。依据周期性局部平稳过程对舰船辐射噪声建模,推导出无噪声干扰及有噪声干扰下的包络线谱强度的数学表达式,获得了包络线谱强度传播衰减的规律,在水声波导中包络线谱声级传播规律与平稳谱一致,但包络线谱高出连续谱的强度的衰减取决于随信噪比变化的调幅深度修正因子。包络线谱强度数值预报方法如下:先利用传播衰减的数值方法例如用简正波方法波数积分方法PE方法等求出平稳辐射噪声的传播衰减,再求信噪比,最后依据调幅深度修正因子获得包络线谱强度降低的分贝数,预报出在水声波导中任意一点包络线谱信号高度。该理论和数值预报方法具有创新性,实用,简单,适合工程应用。     

Phase conjugation in an acoustic waveguide

A method for holographic observation of sound sources and passive inhomogeneities in acoustic waveguides is proposed. The method is based on the principle of coherent phase conjugation. A possibility of visual observation of both sound sources and stationary inhomogeneities of different kinds is experimentally verified.     

Statistics of the ray travel times in oceanic acoustic waveguides under chaos conditions

Data processing for the numerical calculation of the ray paths in both range-dependent and range-independent oceanic acoustic waveguides is performed. The obtained statistical data are used to plot empirical distribution functions of the chaotic-ray random parameters. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 3, pp. 196–211, March 2007.     

基于声线理论的水声被动定位原理

本文论述以声线理论信道模型为基础的水声被动定位原理。文中运用声线理论建立水下声信道的数学模型,求解联结声源与接收器的本征声线,分析本征声线的到达角结构(DOAArrivingStructure)与时延谱到达结构(TDSArrivingStructure),以及它们与未知声源位置的关系。通过空一时二维到达结构的匹配处理,实现对声源的被动定位。与通常的基于简正波理论的被动定位方法相比,声线法被动定位实现简便,运算量小,不要求太大的基阵孔径,而且定位性能对环境参数较不敏感,因而具有很好的实际应用前景。     

A spherical acoustic source in an ideal waveguide

The acoustic field of a spherical source in an ideal waveguide is considered with allowance for the diffraction by the source. The consideration uses the previously obtained results on the diffraction by a spherical source in a halfspace with ideal boundaries. The resultant field is shown to be representable as an infinite sum of the fields of some equivalent sources. The errors that appear when the number of these sources is limited are estimated. The field produced by the sphere in an ideal waveguide is calculated with and without allowance made for the scattering.     

Wideband time-reversal imaging of an elastic target in an acoustic waveguide

Time-reversal is addressed for imaging elastic targets situated in an acoustic waveguide. It is assumed that the target-sensor range is large relative to the channel depth. We investigate the theory of wideband time-reversal imaging of an extended elastic target, for which the target dimensions are large relative to the principal wavelengths. When performing time-reversal imaging one requires a forward model for propagation through the channel, and the quality of the resulting image may be used as a measure of the match between the modeled and actual (measured) channel parameters. It is demonstrated that the channel parameters associated with a given measurement may be determined via a genetic-algorithm (GA) search in parameter space, employing a cost function based on the time-reversal image quality. Example GA channel-parameter-inversion results and imagery are presented for measured at-sea data.     

Development of an accelerometer-based underwater acoustic intensity sensor

An underwater acoustic intensity sensor is described. This sensor derives acoustic intensity from simultaneous, co-located measurement of the acoustic pressure and one component of the acoustic particle acceleration vector. The sensor consists of a pressure transducer in the form of a hollow piezoceramic cylinder and a pair of miniature accelerometers mounted inside the cylinder. Since this sensor derives acoustic intensity from measurement of acoustic pressure and acoustic particle acceleration, it is called a p-a intensity probe. The sensor is ballasted to be nearly neutrally buoyant. It is desirable for the accelerometers to measure only the rigid body motion of the assembled probe and for the effective centers of the pressure sensor and accelerometer to be coincident. This is achieved by symmetric disposition of a pair of accelerometers inside the ceramic cylinder. The response of the intensity probe is determined by comparison with a reference hydrophone in a predominantly reactive acoustic field.     

Design of an acoustic bending waveguide with acoustic metamaterials via transformation acoustics

Transformation acoustics is employed to design an acoustic bending waveguide. A two-dimensional square area with anisotropic and homogeneous material properties is transformed into a fan-shaped area with anisotropic and inhomogeneous material properties to rotate the direction of beam propagation. An alternating layered structure is considered to approximate a medium with anisotropic material properties. From the calculation results, the transformation medium can be realized by an alternating layered structure consisting of water and fluid with negative mass density. We propose that an acoustic metamaterial composed of three layers in water background can be designed to replace negative mass density fluid. The effective mass density and bulk modulus of the system that is composed of the acoustic metamaterial and water are dependent on the incident frequency and the geometric size of the acoustic metamaterial. We tune the geometric size of the acoustic metamaterial to approach the corresponding mass density distribution of the negative mass density fluid at a specific frequency. Thereby, the acoustic bending waveguide designed by using transformation acoustics can be achieved by the acoustic metamaterials.     

A tunable gas sensor using an acoustic waveguide

A tunable gas sensor using surface acoustic waves (SAW) is described. It is designed on the basis of a waveguide delay line fabricated on a piezoelectric substrate made of 128° Y-cut LiNbO₃. A voltage applied between the waveguide and two electrodes causes a local change in the properties of the substrate near the waveguide and differently affects the sensor’s response to the vapors of various analytes. Some results of the experimental study of the sensor, which show the change in the selectivity under the effect of voltage, are presented. The analytes used for testing include a number of alcohols and deionized water. The possibilities for employing such a sensor in the sensor arrays of gas analyzers of the electronic nose type are discussed.     

水声信道的修正二进制对称信道模型和纠错码的性能分析

介绍了用海试数据建立水声信道修正二进制对称信道(GBSC)模型的方法.用模型计算的错组率分布p(n, ≥ m)与实测数据吻合较好,说明GBSC模型能较好地描述水声信道,而且GBSC模型具有计算简单使用方便的优点。本文还对不同码长的BCH码的性能进行了仿真分析。     

Simulation of the lower boundary of an acoustic waveguide

The paper discusses simulation of the lower boundary of an acoustic waveguide. The applicability and relationship of rigid bottom and fluid half-space models are studied as a function of the bottom sediment parameters. The influence of bottom losses on the sound field characteristics in a waveguide is studied. Examples of numerical simulation are given.

     

Energetic analysis of an actively controlled one-dimensional acoustic waveguide

The aim of this work is to show the energetic behavior when an active noise controller is applied in a one-dimensional waveguide, namely an ideal duct under the first critical frequency. In order to model the duct, a spectral element method, which is shown to be more practical for analyzing pipe networks than other commonly used analytical models, was used. The model used here consists of a duct with two sources, the primary source at one end of the duct, and the secondary source at the middle section. The error sensor was placed downstream from secondary source, and the other end of the duct was open with no flange. Three optimal control methods were applied: minimization of the potential energy density, minimization of the active intensity, and minimization of the total acoustic power radiated by the sources. It was observed that the three control methods achieved the same final result, and when the volume velocity of the secondary source was driven to the optimal volume velocity, neither the primary source nor the secondary source radiated any acoustic power. Furthermore, the controlled duct was equivalent to a duct opened-ended at the secondary source position with radiation impedance equal to zero.     

分层砂底对浅海信道声传播影响的研究

推导有指向性脉冲声源在海底是分层结构的浅海中声场的积分表达式;分别仿真了爆炸声源和指向性脉冲源在浅海信道中传播的信号波形,其中假设了海底的沉积层和基底分别由水浸泡的砂和固态介质构成,砂底的参数数值用孔隙介质理论和实测相结合的方法进行选择;此外,在用砂和玻璃珠分别模拟砂层海底的水池内,观测了指向性脉冲源在不同接收点的信号的波形;结果表明:仿真波形的包络得到实验的印证。从而证明本文建立的指向性脉冲源在具有砂层海底的浅海中声场模型是可行的,可用于预报海洋环境参数对接收波形的影响,为水下通信、声呐信号设计与处理提供参考信息。     

Piston acoustic radiator in an impedance screen of a Pekeris waveguide

A model problem of seismic hydroacoustics is studied for a piston radiator inserted in an impedance screen that coincides with the lower boundary of a Pekeris waveguide. The radiation resistance of the piston is numerically calculated as a function of the screen type and parameters of the radiator and the waveguide.     

Non-linear acoustic radiation by an underwater vibrating spherical shell

I.IntroductionMostofthepublishedstudiesontheacousticwaveradiationfromelasticbodyconcen-tratedon1ineartheory.However,iftheamplitudeislargeandthefrequencyishigh,theresultingsoundwavepropagatinginthemediumwillgenerateconsiderablenonlineardistor-tion.Sothest.di.s[1]inthisfieldarelimited.Inthispaperwetreatedasphericalshell.Itconsistsoftwoaspects:oneisthestructuralresponseofasphericalshellinacousticfield.Becausethenonlineareffectofacousticwavecumulateswithpropagatingdistance,itisnegligibleonthesph…     

Focusing of a sound beam in an underwater waveguide using a vertical antenna

We propose a method for calculating the amplitude-phase distributions of signals on the elements of an emitting antenna for generating narrow wave beams and field focusing at given points of the waveguide. The efficiency of the method is confirmed by the data of a field experiment conducted in Lake Ladoga.     

水声换能器研究新进展

文章综述了几种典型结构水声换能器近些年的新发展,包括:弯张换能器、圆柱面辐射型换能器、纵向换能器等等,主要介绍这些结构类型水声换能器的设计新思想和多方面优化改进的新成果。