球形障板对矢量水听器接收性能的影响

矢量水听器可以同步共点测量声场空间一点处的声压和质点振速的各个分量,因此其被广泛应用于水声测量、探测、通信等领域。矢量水听器在水声测量的应用中会受到安装载体散射声场的影响,而这种载体可以看作为障板,由于障板的存在使散射声场的分布发生改变,以及矢量水听器的接收性能下降。仅以绝对硬边界为例,对球形障板的散射声场进行了理论计算和仿真分析。并且对带障板条件下矢量水听器的接收指向性的变化进行了仿真研究。结果显示,从散射声场分布图可以直观看出声场发生的变化,矢量水听器的接收性能变化与障板的尺寸、与障板距离远近、声波发射频率等因素有关。     

弹性球壳声散射对矢量水听器测向影响研究

以平面波在弹性球壳上声散射理论为基础,建立了弹性球壳近场声散射对矢量水听器目标定向性能影响计算模型,分析了入射声波信号频率、入射角度以及矢量水听器安装位置对目标定向的影响。计算和理论分析结果表明．弹性球壳声散射对矢量水听器测向性能的影响与壳体散射特性和水听器安装位置密切相关,在低频和高频段测向误差相对比较小,而在中频段则测向误差比较大,可通过选择工作频段,或者采用声学处理,降低壳体声散射强度,减小对矢量水听器测向性能的影响。研究结果为矢量水听器工程应用奠定了理论基础。     

球形壳体障板声散射近场矢量特性

为了实现矢量水听器在水面或水下载体上的工程应用,研究了球形壳体障板声散射近场矢量特性。采用弹性薄壳理论结合边界条件导出了球形壳体障板声散射的声压和质点振速表达式,给出相应的声强表达式。数值计算了球形壳体障板声散射的近场特性,重点关注其近场矢量特性。理论分析和数值计算结果表明,由于球形壳体障板的散射作用,声压场和质点振速场表现为复杂的干涉结构;质点振速方向和声源方位不一致;声压和质点振速不再同相;声强方向也不再反映声源方位。本文结果为矢量水听器在球形载体和球形障板条件下的工程应用提供理论依据。     

基于单矢量水听器的目标检测及测向系统

介绍一种基于压差矢量水听器的目标检测及测向系统,它采用TI公司的MSP430F149低功耗单片机作为处理硬件,以RS232串口传输方式,在计算机终端采用LabWindows／CVI软件编写了显示软件,对单片机的处理结果进行实时显示。经过实验室调试及水池试验,试验结果表明,本系统具有目标检测能力及较高的测向精度。     

带障板水听器基阵阵列流形的边界元计算及验证

建立一种复杂结构水听器基阵阵列流形计算模型。该模型运用声场计算的边界元方法,通过计算任意散射体表面声场分布,求出基阵阵元位置处声场响应,进而得到基阵阵列流形;基于该阵列流形,运用波束设计方法求出阵元权值,分别利用实测和理论阵列流形得到基阵实测波束以及理论波束。针对安装在半球形硬质铝壳体上的圆弧阵进行的水池实验,实验结果表明实测阵列流形和基于边界元方法的计算结果基本吻合,实测波束和理论波束相差不大,并且性能均优于按无指向性点接收器经相位补偿后相加所得到的波束。     

有限平面障板对低频指向性的影响

为提高对水下目标的远程探测能力,降低水下航行体系统工作频率不失为一种较易实现的好方法。矢量传感器在各向同性噪声场中可以获得较大的低频检测增益,且其低频指向性好、体积小、重量轻,但是将矢量传感器安装在水下航行体头部的导流罩内时,传感器的后障板对其指向性有影响,从而影响水下航行体对目标定向的能力。该文从声学原理出发,对平面波在有限平面障板边界上的声压场和振速场进行了理论分析,在此基础上建立了矢量传感器在有限平面障板下的指向性模型,并通过计算机仿真分析,研究了有限障板对低频指向性的影响。设计了实验室试验系统,并进行了试验验证。试验结果表明,仿真分析与水池试验结果一致,证明了该模型的正确性,为减小有限障板对矢量传感器性能的影响奠定了基础。     

弹性球壳声散射对矢量传感器测向精度的影响

由无指向性的声压传感器和具有偶极子指向性的振速传感器组成的矢量传感器,被应用于水声技术的各个领域;在实际应用过程中,常常把矢量传感器固定在某个水下平台上,而平台产生的散射场会使矢量传感器的接收声场发生畸变,进而影响其测量结果。本文以实际应用为背景,建立了弹性球壳障板的声散射场对矢量传感器测向性能影响的模型,并通过仿真分析了不同入射频率、不同观察距离、不同球壳厚度和半径条件下障板对矢量传感器测向精度的影响,研究结果为矢量传感器在水声测量中的应用提供理论支撑。     

障板对于平板声辐射特性的影响分析

采用单层势和双层势求解和比较有障板和无障板的声辐射特性。由边界积分方程,分别推导有障板和无障板的声压积分方程,根据交界相容性条件,获取二重积分形式的平板表面声压和振速。进一步将结构的动力方程代入有障板和无障板形式的振速方程中,离散声压差值和板的位移为振动模态叠加的形式,获得二重积分形式的声辐射阻抗,从而求解振动模态系数,确定声辐射特性参数。以水下简支矩形板为例计算对比了声辐射参数,分析障板对薄板声辐射特性的影响。     

偏振状态下球形粒子的散射相位函数研究

本文根据散射相位函数的定义,得到了偏振状态下单个粒子散射相位函数的表达式,并且通过研究发现以下规律:1)粒子半径越小,极值差随散射角越趋向于对称分布;2)散射角在0～0.025π以及O.997π～π之间,散射相位函数随极化角基本不变;3)散射角在O.025π～0.997π之间,散射相位函数随极化角变化明显.同时比较了偏振状态下多粒子和单粒子散射相位函数随散射角和极化角的分布.最后从大气中光传输理论出发,建立了非偏振状态与偏振状态下散射相位函数的关系,为大气散射回波功率测量以及近似散射相位函数的研究提供参考.     

有限大障板上轴对称扬声器声压级的近似计算方法

扬声器声压级测试一般是将扬声器安装在矩形标准障板上进行的,而要通过仿真分析方法准确计算该扬声器在这种声场条件下的声压级,以往只能采用3D模型,其计算量非常大。提出了一种近似计算方法,将有限大障板近似为很多个扇形障板块的组合,再利用2D轴对称模型的仿真分析方法计算每个扇形障板块影响下的声压,进而得到轴对称扬声器安装在该有限大障板上的声压级。这种方法使仿真分析模型与实际测试相符合,同时也避免了规模庞大的3D仿真计算。     

水下刚硬体声散射场计算及分析

针对水下任意形状刚硬体,建立了其声散射T矩阵法计算模型。利用物体的几何对称性,提出了各种简化计算Q矩阵的方法。以两端有半椭球顶的有限长圆柱体为例,分别计算了具有不同长宽比或者是不同端部几何形状的有限长圆柱体的反向散射和前向散射函数。深入讨论了有限长圆柱体的镜反射波和Franz波的干涉物理模型,以及其圆柱体中段长度对散射场的影响,并对得到的计算结果给出了合理的物理解释。计算结果同时也表明T矩阵法是一种很简便实用的计算水下物体远场散射的方法。     

A distortion measure to validate and generate curved high‐order meshes on CAD surfaces with independence of parameterization

A framework to validate and generate curved nodal high‐order meshes on Computer‐Aided Design (CAD) surfaces is presented. The proposed framework is of major interest to generate meshes suitable for thin‐shell and 3D finite element analysis with unstructured high‐order methods. First, we define a distortion (quality) measure for high‐order meshes on parameterized surfaces that we prove to be independent of the surface parameterization. Second, we derive a smoothing and untangling procedure based on the minimization of a regularization of the proposed distortion measure. The minimization is performed in terms of the parametric coordinates of the nodes to enforce that the nodes slide on the surfaces. Moreover, the proposed algorithm repairs invalid curved meshes (untangling), deals with arbitrary polynomial degrees (high‐order), and handles with low‐quality CAD parameterizations (independence of parameterization). Third, we use the optimization procedure to generate curved nodal high‐order surface meshes by means of an a posteriori approach. Given a linear mesh, we increase the polynomial degree of the elements, curve them to match the geometry, and optimize the location of the nodes to ensure mesh validity. Finally, we present several examples to demonstrate the features of the optimization procedure, and to illustrate the surface mesh generation process. Copyright © 2015 John Wiley & Sons, Ltd.     

Efficient DG‐like formulation equipped with curved boundary edges for solving elasto‐acoustic scattering problems

A Discontinuous Galerkin (DG)‐based approach is proposed for computing the scattered field from an elastic bounded object immersed in an infinite homogeneous fluid medium. The proposed method possesses two distinctive features. First, it employs higher‐order polynomial‐shape functions needed to address the high‐frequency propagation regime. Second, it is equipped with curved boundary edges to provide an accurate representation of the fluid–structure interface. The most salient benefits resulting from the latter feature, as demonstrated by the numerical investigation, are the following: (i) an improvement by—at least—two orders of magnitude on the relative error and (ii) the disappearance of spurious resonance frequencies in the surrounding fluid medium. In addition, the reported numerical results reveal that when using cubic polynomials with less than three elements per wavelength, the proposed DG method computes the scattered field with a relative error below 1% for an elastic scatterer of about 30 wavelengths. This observation highlights the potential of the proposed solution methodology for efficiently solving mid‐frequency to high‐frequency elasto‐acoustic scattering problems. Copyright © 2014 John Wiley & Sons, Ltd.     

分舱段圆柱壳声散射数值和试验研究

基于有限元方法建立了填充不同介质的有限长分舱段圆柱壳声散射数值计算模型,仿真了填充空气-空气、空气-水、水-水三类两舱段圆柱壳声散射特性,并完成了三类两舱段圆柱壳体声散射试验,获取和分析了两舱段圆柱壳体声散射的时间角度谱和频率角度谱特性。利用物理声学方法分析了壳体表面、端面以及内部填充水介质对散射声场的影响,揭示了两舱段圆柱壳声散射频率角度谱中呈现的干涉条纹特征形成机理,为水下分舱段目标,如水下无人航行器的主动声呐探测和识别提供理论支撑。     

A fictitious domain decomposition method for the solution of partially axisymmetric acoustic scattering problems. Part I: Dirichlet boundary conditions

We present a fictitious domain decomposition method for the fast solution of high‐frequency acoustic scattering problems characterized by a partially axisymmetric sound‐soft scatterer. We apply this method to the solution of various mockup submarine problems, and highlight its computational advantages and intrinsic parallelism. Copyright © 2002 John Wiley & Sons, Ltd.     

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。     

A fictitious domain decomposition method for the solution of partially axisymmetric acoustic scattering problems. Part 2: Neumann boundary conditions

We present a fictitious domain decomposition method for the fast solution of acoustic scattering problems characterized by a partially axisymmetric sound‐hard scatterer. We apply this method to the solution of a mock‐up submarine problem, and highlight its computational advantages and intrinsic parallelism. A key component of our method is an original idea for addressing a Neumann boundary condition in the general framework of a fictitious domain method. This idea is applicable to many other linear partial differential equations besides the Helmholtz equation. Copyright © 2003 John Wiley & Sons, Ltd.     

Monte Carlo simulation of Stokes vectors of polarized light scattering from two-dimensional random rough surfaces

A Monte Carlo model was established to simulate polarized scattering fields of two-dimensional rough surfaces based on the Kirchhoff approximation. Based on this model, numerical studies of the hemispherical distribution of Stokes vectors of scattered light from dielectric and metal rough surfaces were carried out. These surfaces have Gaussian distributions with correlation length of 3.1?µm and standard deviation varying between 0.1 and 0.6?µm. The results reveal that the V component of metal surfaces has peaks antisymmetric with the incident plane, whereas the V component of dielectric surfaces is almost zero. We consider that this property of the V component would provide a new method which could be used to distinguish the target material.