小斜率近似方法分析粗糙界面声散射问题

利用小斜率近似方法计算了起伏海面的声散射特性,得到了具有高斯分布粗糙海面的平均反射系数（即镜反射系数）计算公式,并与微扰法和Kirchhoff近似做了比较,结果表明小斜率近似是一种非常有效的分析起伏表面散射特性的近似方法。最后讨论了海面镜反射系数随海面的不平整度（波浪的均方根高度）、声波频率和声波入射方向的变化关系,得出了只有在声波波长和起伏波浪高度可比拟时,才有明显的镜反射的结论。这为分析浅海目标声散射特性时,选择是否需要考虑海面（海底）所引起的多途效应提供了理论依据。  

黄海中部高频反向体积声散射的观察

本文利用频率为２００ｋＷｚ的垂直探鱼仪对黄海中部夏季反向体积声散射进行了观察，对散射回波信号作了录音。发现晚上散射很强，白天则很弱。经给出了计算机处理后不同深度散射信号随时间的变化，获得了散射体在黎明天亮时垂直向下移动的动态记录和由散射层垂直起伏所反映出海洋内波图象。  

A new acoustic spectroscopy: Resonance spectroscopy by the MIIR

Recent and remarkable advances in the experimental study of acoustic scattering from targets immersed in water are leading to a new spectroscopy: resonance acoustic spectroscopy. The discovery and improvement of an intriguing method, the Method of Isolation and Identification of Resonances (MIIR), has made possible experimental determination of the eigenfrequency spectra of aluminum-elastic cylinders and cylindrical shells. This method gives a quasilinear resonance spectra. In addition, it shows the importance of circumferential waves which generate standing waves. They allow us to explain the reradiation of targets after the end of insonification. The MIIR has numerous applications, especially in underwater acoustics and nondestructive testing.  

三维障碍物形状近场反演的一种快速算法

文章研究了从点声源散射场的有限孔径近场测量信息来再现多个三维障碍物形状的反问题。指出了数值求解这类反问题的一种简单快速逄。数值结果表明了该算法是有效和实用的。  

A modified Burton-Miller algorithm for treating the uniqueness of representation problem for exterior acoustic radiation and scattering problems

A modification to the Burton-Miller algorithm is formulated for exterior acoustic radiation and scattering problems which resolves the uniqueness of representation problem associated with the Helmholtz integral equation method (HIEM) at the interior eigenvalues. In particular, this modification reduces the required number of integral equation evaluations and allows for the continued use of the popular higher-order Lagrangian shape functions. Several example problems are considered to demonstrate the difficulties and subtleties of the uniqueness of representation problems associated with the Helmholtz integral equation method and to demonstrate the effectiveness of the modified Burton-Miller algorithm in overcoming these problems.  

A meshless numerical identification of a sound-hard obstacle

We propose a simple meshless method for detecting a rigid (sound-hard) scatterer embedded in a host acoustic homogeneous medium from scant measurements of the scattered near field. This inverse problem is ill-posed since a solution may not be unique and furthermore, small errors in the input data cause large errors in the output solution. We develop a nonlinear minimization regularized method of fundamental solutions (MFS) for obtaining the numerical solution of the inverse problem in question. Although the MFS is restricted to homogeneous media with constant wavenumber, it is easy to use and simple to implement in higher dimensions. The proposed scheme is tested on several numerical examples and its stability is investigated by inverting measurements contaminated by random noise.  

随机起伏界面声散射的实验与理论研究

进行了二维粗糙海面声波散射特性的水池实验,测量了不同入射角、散射角以及方位角条件下所对应的散射强度。实验通过不同位置风扇对水面的吹拂获得粗糙水面,分别对水平面上互相垂直的两个方向上的水面波高变化进行了测量,利用周期图法估计出这两个方向上的空间功率谱,验证了实验中的粗糙水面是各向同性的。利用改进的空间域处理技术去除了总声波信号中的直达波和其他固定位置散射体的散射信号,获得了粗糙水面的声波散射信号。利用小斜率近似方法计算了二维粗糙海面的声散射特性。实验与模拟计算结果比较,证实了计算二维粗糙海面声波散射特性的小斜率近似方法的有效性与准确性,相互印证了实验与理论。  

近场声全息测量阵架的设计与分析

全息测量系统设计的关键是测量全息面测点复声压（幅值和相位）的真实数据,介绍了自行设计的近场声全息（NAH）测量的传声器线阵扫描系统。利用边界元法计算了传声器线阵架结构表面声散射对阵上传声器测量全息复声压的影响,提出了敷设吸声材料以提高测量精度的措施;对在线阵架表面敷设吸声材料后的声散射效应仿真结果表明,吸声材料能够有效降低声散射效应,可以提高测量精度。  

Scattering from two eccentric spheroids: Theory and numerical investigation

In this paper, the direct acoustic scattering problem of a point source field by a penetrable spheroidal scatterer hosting an impenetrable spheroidal body of arbitrary position, size and orientation, is considered. The application background corresponds to the near field measurement of the acoustic field, scattered by a soft-tissue organ including a hard inhomogeneity. The methodology incorporates two independent techniques which are modified appropriately to fit together and are combined for the first time: first, the Vekua method, which is based on the well known Vekua transformation, providing with fully analytic solutions of Helmholtz equation and second, the method of auxiliary sources in order to represent the net wave contribution of the inhomogeneity. The satisfaction of transmission and boundary conditions is accomplished via the collocation method while the wave character of the fields and the outwards propagating property of the exterior wave are implicitly guaranteed in exact form through the analytic nature of the method. Special effort has been devoted to the self-evaluation of the method by constructing and calculating an indicative error function representing the failure of satisfaction of the boundary conditions on a rich grid over the interfaces, much larger than the set of collocation points, where the error is by construction negligible. This numerical approach leads to very reliable results. The determination of the near scattered field as well as of the far-field pattern are the final outcomes of the present work, providing a thorough solution of the direct scattering problem and giving insight to the corresponding inverse problem.  

Partial-differential-equation-constrained amplitude-based shape detection in inverse acoustic scattering

In this article we discuss a formal framework for casting the inverse problem of detecting the location and shape of an insonified scatterer embedded within a two-dimensional homogeneous acoustic host, in terms of a partial-differential-equation-constrained optimization approach. We seek to satisfy the ensuing Karush–Kuhn–Tucker first-order optimality conditions using boundary integral equations. The treatment of evolving boundary shapes, which arise naturally during the search for the true shape, resides on the use of total derivatives, borrowing from recent work by Bonnet and Guzina [1–4] in elastodynamics. We consider incomplete information collected at stations sparsely spaced at the assumed obstacle’s backscattered region. To improve on the ability of the optimizer to arrive at the global optimum we: (a) favor an amplitude-based misfit functional; and (b) iterate over both the frequency- and wave-direction spaces through a sequence of problems. We report numerical results for sound-hard objects with shapes ranging from circles, to penny- and kite-shaped, including obstacles with arbitrarily shaped non-convex boundaries. Partial support for this work was provided by the US National Science Foundation under grant award CMS-0348484.