Calculation of temporal, angular, and intensity characteristics of the sound field in a coastal area with an arbitrary bottom relief and a constant sound speed in the medium

Computational algorithms and some computed data are presented for the total sound field in a waveguide whose depth arbitrarily depends on two horizontal coordinates. The sound speed is supposed to be constant, and the bottom slopes are considered as small. The algorithm involves three steps. First, horizontal rays, i.e., horizontal projections of the real rays multiply bottom-and surface-reflected, are calculated. Second, the horizontal rays are set up to a point. Third, the real rays are set up to a point. The computational accuracy is analyzed for a homogeneous wedge lying on a halfspace. Calculations are carried out for a coastal region of the ocean.     

Space-time sound field interference in the horizontal plane in a coastal slope region

The nonstationary interference structure formed in the horizontal plane in the field of a point source in a coastal slope region is analyzed on the basis of the space-time horizontal ray concept. For a model that includes the typical bathymetry and sound velocity profile, the space, time, and frequency dependences of the sound field are considered for different waveguide modes. The characteristic scales of the field variability in space and time are estimated. The frequency-time diagram is analyzed for the region of the interference of direct and reflected waves. The variability of the field interference structure in the presence of mesoscale perturbations is considered.     

Space anisotropy of bottom reverberation in the coastal zone

A method for calculating the bottom reverberation in a coastal zone with allowance for the three-dimensional bottom topography, which affects the spatial anisotropy of the incoming reverberation signal, is proposed. The method is based on the ray approach in combination with the use of the ray invariant. Examples of calculating the monostatic bottom reverberation level for one of the coastal regions with a complex bottom topography including the coastal line and an underwater elevation are presented.     

The sound field in a hydroacoustic waveguide with an uneven hard bottom

An analytic representation is constructed for a nonaxially symmetric sound field to simulate a hydroacoustic waveguide the bottom of which is hard and has an axially symmetric relief. A numerical analytic method for finding the velocity potential is proposed, for which undetermined coefficients for normal modes are determined from a corresponding infinite system of algebraic equations. The sound fields are studied with for variations of the problem parameters.     

深海表面层声速剖面变化对声传播的影响

在我国部分海域，表面声速常常在较短的时间内从弱正梯度变为弱负梯度，这将对表面附近的声传播产生巨大影响。本文通过数值模拟的方法，讨论了表面层声速梯度变化对声传播的影响，同时解释了某次海上实验出现的异常现象：在同一地点同一航向，前后两天海况相同，水文相差不大，第一天的实验可以在50km之外接收到信号，而第二天只能在30km处才能收到信号。     

R-matrix method for a surface with one groove of arbitrary profile

The R-matrix propagation algorithm is applied to solve the problem of electromagnetic scattering from a perfectly conducting plane surface with one groove of arbitrary profile. Using the multilayer approximation, the fields inside each layer are written as modal expansions. The reflected intensity is obtained in both the fundamental cases of polarization, which are treated separately. Numerical examples are shown for several profiles of the groove, and comparisons with results known from physical optics are presented for the validation of the method.     

Canonical path-integral quantization of yang-mills field theory with arbitrary external sources

Some modification of source terms is proposed for gauge field theories. In theSU(2) Yang-Mills theory with arbitrary external sources a canonical quantization procedure leads to a Lorentz-invariantS-matrix only when Fermi statistics is imposed on ghost fields. The usual source terms lead to a result that breaks Lorentz invariance and is singular when external chargesJskin0 vanish. The cases of the Abelian scalar electrodynamics and theSU(2) Yang-Mills field with external currents (Jskino=0,Jskini 0) are also discussed.     

Effect of the sound velocity stratification in the bottom sediment layer on the diffraction focusing of an acoustic field in a shallow sea

It is shown that an increase in the sound velocity gradient in the bottom sediment layer results in the formation of additional zones of diffraction focusing of the acoustic field generated by a vertical line array in the water layer. It is also established that, depending on the sound velocity step at the upper boundary of the sediment layer, the diffraction focusing of the acoustic field in the main focusing zones can be enhanced or reduced.     

Correlation in the velocity of a Brownian particle induced by frictional anisotropy and magnetic field

We study the motion of charged Brownian particles in an external magnetic field. It is found that a correlation appears between the components of particle velocity in the case of anisotropic friction, approaching asymptotically zero in the stationary limit. If magnetic field is smaller compared to the critical value, determined by frictional anisotropy, the relaxation of the correlation is non-oscillating in time. However, in a larger magnetic field this relaxation becomes oscillating. The phenomenon is related to the statistical dependence of the components of transformed random force caused by the simultaneous influence of magnetic field and anisotropic dissipation.     

Characteristic features of the sound field formation near the bottom of a shallow sea

Detailed calculated data are presented for the angular, temporal, and energy structures of the sound field at the points of localtion of a horizontal line array of receivers (at 250-m intervals) in a shallow sea. The array is deployed near the bottom of a 200-m-deep waveguide along a sound propagation track, at distances from 20 to 30 km from a source generating a signal in the kilohertz frequency range. The influence of a sand or mud bottom on the intensity of signals arriving along single rays is numerically estimated for winter and summer conditions of sound propagation in a specific region of the Barents Sea.     

Wave field synthesis of moving virtual sound sources with complex radiation properties

An approach to the synthesis of moving virtual sound sources with complex radiation properties in wave field synthesis is presented. The approach exploits the fact that any stationary sound source of finite spatial extent radiates spherical waves at sufficient distance. The angular dependency of the radiation properties of the source under consideration is reflected by the amplitude and phase distribution on the spherical wave fronts. The sound field emitted by a uniformly moving monopole source is derived and the far-field radiation properties of the complex virtual source under consideration are incorporated in order to derive a closed-form expression for the loudspeaker driving signal. The results are illustrated via numerical simulations of the synthesis of the sound field of a sample moving complex virtual source.     

Sound field structure produced by tone sources in the Kurile-Kamchatka region of the Pacific Ocean with a surface channel and wind waves

Results of the experimental studies of sound signal propagation in the continental wedge of the northwestern Pacific, near the eastern coast of the Kamchatka Peninsula, are presented. The signals are produced by highly stable tone sources. The experiments are carried out in winter, in the presence of a strong surface sound channel and intense wind waves, at frequencies of 100, 230, and 400 Hz, on a 1000-km-long path. The signal transmission is performed by continuously towing the sound sources at a depth of 50±5 m with a speed of 4.5–5 knots, for 115 hours. The decay of the sound field level with distance is studied as a function of the sea state and the frequency. The results of the experiments, including the sound field decay along the path, are compared with the calculations for different sea states.     

单层传声器阵列重建相干声场的近场声全息方法研究

针对传声器阵列两侧存在相干声源的非自由声场重建问题,提出基于球面谐波函数扩展近场声全息理论的相干声场重建方法。该方法在已知测量面两侧声源几何位置时,使用单层传声器阵列获取测量面处的声压分布,通过最小二乘法获得与目标声源和干扰噪声源响应对应的最优球波函数扩展项数和最优系数向量,结合测点位置的空间坐标进行声波分解,并分别重建出各声源在测量面上的声压分布。为了验证方法的有效性,分别给出了相干噪声源为球形声源和非球形声源的仿真验证,并在全消声室内对双扬声器产生的相干声场的重建进行了实验验证。结果表明:该方法对球形声源和非球形声源干扰下的声场重建都具有较好的效果,球形声源干扰下的重建精度更高。     

单层传声器阵列重建相干声场的近场声全息方法研究

针对传声器阵列两侧存在相干声源的非自由声场重建问题,提出基于球面谐波函数扩展近场声全息理论的相干声场重建方法。该方法在已知测量面两侧声源几何位置时,使用单层传声器阵列获取测量面处的声压分布,通过最小二乘法获得与目标声源和干扰噪声源响应对应的最优球波函数扩展项数和最优系数向量,结合测点位置的空间坐标进行声波分解,并分别重建出各声源在测量面上的声压分布。为了验证方法的有效性,分别给出了相干噪声源为球形声源和非球形声源的仿真验证,并在全消声室内对双扬声器产生的相干声场的重建进行了实验验证。结果表明:该方法对球形声源和非球形声源干扰下的声场重建都具有较好的效果,球形声源干扰下的重建精度更高。     

The local autocorrelation time near the surface of a system with uniaxial anisotropy in a transverse field

A three-dimensional semi-infinite system with strong uniaxial anisotropy ina transverse field is considered. The behaviour of the local autocorrelation time for the component of the order parameter in the direction parallel to the easy axis near the second-order phase transition for this component induced by the transverse field is given. The effect of the surface on this behaviour is discussed. The Landau approximation is used.     

楔形弹性海底声矢量场分布规律研究

提出了基于弹性抛物方程的声矢量场计算方法,计算了楔形弹性海底的海洋环境中甚低频声矢量场和弹性海底地震波场分布,研究了声源深度和声源频率对声场分布的影响,仿真结果表明声波在具有弹性楔形海底的海洋环境中传播时存在能量泄漏现象,利用简正波理论解释了能量泄漏位置可由水深—波长比确定。     

Researches on the distribution law of vector sound field in elastic wedge bottom

The method based on elastic parabolic equation method for calculating the sound vector field has been studied.The vector field in water and corresponding seismic wave field had been calculated for infra-sound in oceanic environment with elastic wedge bottom.The effects on sound field distribution for different frequency and depth of sound source had been researched,result shows that there is sound energy leakage into the bottom,the position where leakage occurred can be determined by the ratio of the ocean depth to the wavelength,as compared with normal mode theory.     

Temporal formation of optical anisotropy and surface relief during polarization holographic recording in polymethylmethacrylate with azobenzene side groups

The formation of polarization holographic gratings with both optical anisotropy and surface relief (SR) deformation was studied for polymethylmethacrylate with azobenzene side groups. Temporal contributions of isotropic and anisotropic phase gratings were simultaneously determined by observing transitional intensity and polarization states of the diffraction beams and characterizing by means of Jones calculus. To clarify the mechanism of SR deformation, cross sections of SR were characterized based on the optical gradient force model; experimental observations were in good agreement with the theoretical expectation. We clarified that the anisotropic phase change originating in the reorientation of the azobenzene side groups was induced immediately at the beginning of the holographic recording, while the response time of the isotropic phase change originating in the molecular migration due to the optical gradient force was relatively slow.     

Prediction of sound fields in rooms of arbitrary shape: Validity of the image sources method

In order to find the sound pressure field in a rectangular room, the classical modal method may be applied. However, it does not apply to polyhedric rooms of any shape, to which, however, the image sources method may be applied. The two methods are compared for several geometric shapes: two parallel planes (a layer), a rectangular wave guide and a rectangular enclosure. It is shown under what conditions the image sources method can give accurate enough results. A comparison of theoretical and experimental results is presented.