Acoustic response characteristics of unsaturated porous media

By employing the plane wave analysis method, the dispersion equations associated with compressional and shear waves using Santos’s three-phase poroelastic theory were driven. Considering the reservoir pressure, the high frequency corrections and the coupling drag of two fluids in pores, the influences of frequency and gas saturation on the phase velocities and the inverse quality factors of four body waves predicted by Santos’s theory were discussed in detail. The theoretical velocities of the fast compressional and shear waves were compared with the results of the low and high frequency experiments from open publications, respectively. The results showed that they are in good agreement in the low frequency case rather than in the high frequency case. In the latter case, several popular poroelastic models were considered and compared with the experimental data. In the models, the results of White’s theory fit the experimental data, but the parameter b in White’s model has a significant impact on the results. Under the framework of the linear viscoelasticity theory, the attenuation mechanism of Santos’s model was extended, and the comparisons between the experimental and theoretical results were also made with respect to attenuation. For the case of water saturation less than 90%, the extended model makes good predictions of the inverse quality factor of shear wave. There is a significant difference between the experimental and theoretical results for the compressional wave, but the difference can be explained by the experimental data available.     

Acoustic characterization of panel materials under simulated ocean conditions using a parametric array source

A technique for evaluating the underwater acoustic performance of panels under simulated ocean conditions in a laboratory test facility is described. The method uses a parametric array as a source of sound within a test vessel capable of simulating ocean depths down to 700 m and water temperatures from 2 to 35 degrees C. The reflection loss and transmission loss of the test panel may be determined at frequencies from a few kilohertz to 50 kHz. The use of the parametric array enables wideband measurements to be undertaken with short-duration pulses and reduces the effects of diffraction from the panel edges. An acoustic filter is used to truncate the array in order to provide a source-free measurement region and to simplify the measurement process. The difficulties of establishing a parametric array in the confined space of the vessel are outlined, and the experimental procedures adopted are described. The techniques were validated by undertaking measurements on two test objects that have predictable behavior. The potential of the technique is also illustrated with experimental results for test panels for hydrostatic pressures up to 2.8 MPa. An extensive discussion of the measurement limitations is included.     

分层海洋介质中本征声线的快速计算

本文提供一种在恒定水深的水平分层海洋中快速计算本征声线的方法，该方法引入声线跨度的概念，将本征声线分解为若干声线跨度的组合，并以声线常数为自变量建立声线组合方程。利用牛顿下山法迭代求解该方程得到本征声线，极大地提高了计算效率，给定海深，声剖面，声源距离、深度及接收器深度等参数时，应用本方法可计算出若干条本征声线的出射角、到达接收位置时的入射角和传播时间。若附加声源的辐射频率和海底底质等信息，还可     

界面条件下线型超声相控阵声场特性研究

开展了界面条件下线型超声相控阵声场特性的研究.将带有楔块的超声相控阵问题合理简化为液固界面的情况进行讨论.根据射线声学理论,计算了单阵元在液固界面存在时的辐射声场,进而推导了聚焦法则,得到了超声线型阵在液固界面存在时的声场、位移场表达式.对安装在楔块上的相控阵换能器的辐射声场进行了仿真,并讨论了聚焦对换能器轴向和横向声场的影响,结果表明利用聚焦能提高分辨率和灵敏度,但聚焦区域之外声束性能更差,在实际检测中要合理利用聚焦. 关键词： 超声相控阵 界面 声场 聚焦     

Light propagation in stratified anisotropic media

Light propagation in stratified anisotropic media with arbitrary orientation of optic axes smoothly varying from layer to layer is considered. In the WKB approximation, a general expression for the field is obtained. For the case of a uniaxial medium, the normal waves are found and specific features of the light propagation are analyzed. General conditions are obtained that determine the turning points and forbidden zones. It is shown that the developed approach allows one to find trajectories of rays in anisotropic media with arbitrary layered structure.     

Propagation and scattering of light in stratified media

The propagation and scattering of light in stratified media are considered. Based on the Maxwell equations, the present approaches to the solution of these problems are formulated in a unified way. The particular features of the wave propagation in stratified media are discussed. Scalar and vector fields are considered. Media with small-and large-scale regular inhomogeneities are examined. The construction of the Green’s function of the wave equation in a spatially homogeneous medium is discussed. Stratified isotropic and anisotropic media are analyzed. The scattering of light in a stratified medium is studied with emphasis on the Kirchhoff method, as this makes it possible to obtain calculation formulas in a form convenient for comparing the theory with the experiment. The propagation of waves in photonic crystals and the formation of forbidden zones in such objects are briefly considered.     

Small amplitude wave propagation in stratified media

Four mutually connected first order linear differential equations for a system of two waves — constituting a set of mathematical models are developed. Small amplitude wave propagation through stratified media have been studied using the mathematical models. Limiting wave solutions are identified as WKB solutions.One of the authors (M.Khan) acknowledges the support of the University Grants Commission (India).     

Propagation in one-dimensionally stratified time-independent scattering media

We calculate the probability density distributions of the power reflection coefficient, and of the various fluxes of the components of an erstwhile plane wave that propagates in a one-dimensionally stratified slab of a time-independent scattering medium. We determine the second- and fourth-order statistics of the power-fluxes, discuss the relevance of this problem to the localization phenomenon, examine the distribution of the emerging power-flux and the limitations on the assumption that it possesses a lognormal distribution, and finally discuss and rationalize the differences between the above and the corresponding characteristics of the radiation propagating in a time-dependent variant of this problem.     

Traces of a tsunamigenic earthquake in a rotating stratified ocean

In the framework of the linear long-wave theory, we derive a system of equations that describe the potential and vortex residual hydrodynamic fields that arise in a rotating stratified (two-layer) ocean during tsunami generation by coseismic deformations of the ocean bottom. For the model case of a cylindrically symmetric ocean bottom deformation, we find an approximate analytical solution of the problem. Based on this solution, we analyze the specific features of residual fields due to the presence of stratification for conditions that are typical of real tsunami sources.     

分层介质中面波的能量分布

在三维情况下研究了分层介质中Rayleigh和Love面波的能量分布问题,分析了多层介质中柱面面波的能量传播特性.面波是声源与介质分界面相互作用的结果,其能流密度随深度增加很快衰减,但在一定深度处出现极大和极小值.通过数值分析发现只有当径向距离较大时,面波能量传播的速度才等于其群速度.文中还考查了频率、深度、介质层状结构等参数对能量分布的影响.     

Acoustic flux imaging in anisotropic media

A new method for characterizing acoustic flux propagation in anisotropic media is introduced and developed. The technique, which we call ultrasonic flux imaging (UFI), utilizes a pair of water-immersion focused acoustic transducers as a point source and point detector. Raster scanning one transducer produces a transmission pattern which exhibits the anisotropies in acoustic flux known as phonon focusing modulated by interference between sheets of the acoustic wave surface. This internal diffraction is studied theoretically taking into account the anisotropy of the medium, the boundary conditions between the solid and the water, and the pressure fields produced by the transducers. In addition to bulk effects, the images reveal interesting critical-cone structures associated with the water/solid interface. The theoretical predictions agree well with experimental observations in silicon and a number of other materials, including single-crystal metals, insulators, and semiconductors. All measurements are made at room temperature, in contrast to the cryogenic requirements of previous phononimaging techniques. As a new method, UFI holds promise for examining anisotropies in the vibrational properties, and, possibly, electron-phonon coupling in metals and superconductors. The principles and techniques may also have application to non-destructive characterization of textured polycrystalline and composite materials.     

层状介质中的声波场及面波研究

本文在前人基础上,采用B、P、C坐标系研究了层状介质中的声波场及面波特性,理论上发现了一个重要结论及一些新的性质,并数值分析了Rayleigh和Love面波的频散特性。定义了关于Rnyleigh面波的两个物理量β₁(位移的B,P分量比)和β₂(应力的B,P分量比),经理论及数值分析发现:β₁和β₂与介质的层状结构密切相关,是对层状介质进行分析和判断的两个重要物理量。     

平面辐射器截断参量源的辐射声场:模型与实验

提出了一种计算以圆形平面活塞辐射器作发射源的声截断参量阵辐射声场的理论模型。即把由声低通滤波器截断的高频原波参量作用区在活塞辐射器的瑞利距离之内可以看作圆柱型的空间分布源。当活塞辐射器半径与参量作用区的长度相比小得多时。这种截断参量源模型可以退化到 Berktay的线源端射阵模型(End-Fire Line Array)。数值计算与实验的对比表明,按此模型计算得到的参量源辐射声场,尤其是在近轴附近与实验测量符合较好。     

相控圆弧阵声源在TI地层井孔中产生的声场

研究了相控圆弧阵声源在各向异性地层井孔中产生的声场的特征,重点分析了该声源对于地层横波各向异性的方位敏感性,旨在探索一种新的地层声学各向异性测量方法。结果显示:相控圆弧阵声源在地层中可激发多种方位阶数的声场,主要成分为单极子波场和偶极子波场;在HTI地层竖直井中,方位角不同的圆弧阵声源激发的波动的速度不同,相控圆弧阵声源对于地层横波速度的方位各向异性的敏感性主要是它所激发的弯曲波的贡献。相比于传统的正交偶极子声波测井而言,采用相控圆弧阵声源可以评价井附近地层的周向非均质性,可以提高井周测量覆盖次数,提高反演结果的可靠性。另外,相控圆弧阵声源兼具备多极子声源的功能,优化的相位控制方式可以实现方位各向异性的最佳测量。     

Numerical and analytical study of wave processes in periodic stratified media

We study the behaviour of the solutions of the Cauchy problem with discontinuous initial data for nonstandard linear partial differential equations modeling wave processes in periodic stratified media. Asymptotic formulas at large t are derived. The found asymptotic formulas are in a good agreement with the results of numerical experiments done by using the analytical computation system REDUCE 3.8.