利用边界元法计算无界声场中结构体声辐射

建立了无界声场中结构体声辐射的边界元数学模型 .计算中以八节点曲边四边形等参元模拟结构体表面 .利用复合亥姆霍兹积分方程解决了边界元方法在计算声学外问题时解的不唯一现象 .同时利用正则化关系式将复合亥姆霍兹积分方程中的超奇异数值积分转化为弱奇异数值积分 .最后以脉动球和振荡球声辐射为例 ,验证了数值计算结果 ,表明利用边界元方法计算声学外问题时必须考虑解的不唯一问题     

用边界元法计算结构振动辐射声场

讨论了用边界元法计算结构振动辐射声场的数值方法。对计算中的积分奇异性采用三角形斜坐标系、退化单元法进行处理,构造了三角形、四边形线性等参元和四边形二次等参元。对特征频率处解不惟一问题采用ＣＨＩＥＦ加Ｌａｇｒａｎｇｅ乘子法进行处理。构造单元具有简单、规范和精确等优点,可用来计算已知表面振速结构的声辐射,或与相应的结构有限元结合,计算结构的振动辐射声场。以脉动球和辐射立主体为例,计算了结构表面声压、声     

利用边界点法克服振动声辐射计算中解的非唯一性

文章利用边界点法，对振动体外部声辐射在特征频率处解的非唯一性问题进行了研究。文中对非唯一性问题的产生作了说明，并以脉动球和摆动球作为算例，说明了边界点法能够有效地克服在特征频率处解的非唯一问题。     

边界积分方程中近边界点几乎奇异积分的计算

该文针对边界元法存在近边界点力学量计算的困难,给出了一个通用性方法,将近边界点到边界单元的距离参数通过分部积分变换到积分式之外,从而计算出二维问题近边界点参量的几乎强奇异和超奇异积分.该法同样适用于板壳问题的边界元法,尤其是对于将超奇异边界积分方程正则化为强奇异边界积分方程的边界元法,求解近边界点参量更加有效.     

快速计算任意振动体辐射声场的边界单元法

在运用边界单元法离散Ｈｅｌｍｈｏｌｔｚ积分方程的基础上，采用远场近似，提出了一种快速求解任意振动物体辐射声场的数值计算方法。并用该法对实例进行了计算和分析。     

Reissner型板边界点法

文章采用 Reissner型板基本解来构建一系列特解 ,再通过边界点法确定边界元方程系数矩阵的全部元素。解算中不涉及具体插值 ,不用数值积分 ,避免了奇性处理 ,而任意点物理量的计算不依赖于待解的边界未知量 ,算效高 ,精度好。该法还可用来分析其它各类板壳问题 ,无论是各向同性还是各向异性的 ,不同的只是应按各自的基本解来构造全特解场矩阵     

快速计算任意振动体辐射声场的边界单元法

在运用边界单元法离散Ｈｅｌｍｈｏｌｔｚ积分方程的基础上，采用远场近似，提出了一种快速求解任意振动物体辐射声场的数值计算方法，并用该法对实例进行了计算和分析。     

用FEM-BEM法预测箱型振动构件的声场辐射

以Helmholtz积分法为基础,应用有限元(FEM)和边界元(BEM)相结合的方法预测振动构件的辐射声场,推导出适合于计算机应用的预测公式,该预测公式结合补充方程对任意的频率都有效.对箱型结构的振动辐射声场进行了预测和实测,实测结果表明,该预测方法是有效的.     

船舶辅机舱振动与声辐射计算及实验研究

采用有限元／边界元法对船舶辅机舱动力设备引起的振动与声辐射进行了数值计算,并进行了相应的实验研究．根据面导纳概念和基座振动测试曲线求得动力设备作用于船体基座上的激励力,使用有限元程序进行结构模型的振动响应计算,然后采用边界元法对水下辐射噪声进行了计算．计算结果与实验结果之间的误差d 10dB以内,表明本方法具有较好的准确度．在此基础上讨论了不同模型参数对计算结果的影响,计算结果表明在边界元法中按照流体波长采用较粗的网格仍可获得较好精度,而仅采用一个舱段模型计算会存在较大误差．     

瞬态声场特性的时域边界元分析和实验研究

本文利用时域边界元技术从理论和实验上讨论结构振动表面的声辐射特性.由于此法是在时间域内分析声振关系,既可以计算稳态声场特性,又可以计算瞬态声辐射规律,为工程实际问题的理论研究提供一种新的声场预报手段.     

基于分布源边界点法的新型近场声全息技术

文章提出采用分布源边界点法作为近场声全息变换算法,建立了基于分布源边界点法的新型近场声全息理论,该方法避开了采用边界元法时所存在的复杂的变量插值、奇异积分的处理、特征波数处解的非唯一性处理等问题,具有计算速度快、计算精度高、计算稳定性好等优点;针对重建结果对测量误差的高度敏感性,提出采用Tikhonov正则化方法稳定重建过程,抑制了重建误差的影响;提出新型的半自由声场全息重建和预测方法,解决了存在地面反射的声场的全息重建问题,对音箱源的研究验证了文中方法的可行性和正确性。     

Comparison study on spherical wave superposition method and spherical wave source boundary point method for realizing nearfield acoustic holography

In the light of the concept of spherical wave source, the theoretical model of nearfield acoustic holography (NAH) based on the spherical wave superposition method (SWSM), including reconstruction of expansion coefficients, prediction of acoustic field, error sensitivity analysis, regularization method and a searching method with dual measurement surfaces for determining the optimal number of expansion terms, is established. Subsequently, the spherical wave source boundary point method (SWSBPM) and its application in the NAH are introduced briefly. Considering the similarity of the SWSM and the SWSBPM for realizing the NAH, they are compared. The similarities and differences of the two methods are illuminated by a rigorous mathematical justification and two experiments on a single source and two coherent sources in the semi-free acoustic field. And, the superiority of the NAH based on the SWSBPM is demonstrated.     

Landweber iterative regularization for nearfield acoustic holography

In the past twenty years, nearfield acoustic holography (NAH) has become an efficient tool for noise source identification, noise source localization and acoustic field visualization. By measuring the complex pressure or particle velocity on a hologram su…     

Orthogonal spherical wave source boundary point method and its application to acoustic holography

When solving acoustic radiation problem in the routine boundary point method (BPM), the inverse of the particular solution matrix of surface normal velocities is needed and the matrix must be full rank and reversible. However, the type of the particular solution sources is single and the sources are not linear independent, so the locations of the particular solution sources inside the vibrating body must be selected carefully. But, in the routine BPM, the loca-tions are determined by an experiential formula, so the method may be invalid for a complicated vibrating body. In this paper, the construction method of the particular solution sources is improved first, and the singular value decomposition (SVD) technique and the Moore-Penrose pseudoinverse are adopted to realize the inversion. As a consequence, the particular solution matrix of surface normal velocities can be non-full rank and the locations of the particular sources can be determined easily. On the basis of the improved BPM, the spherical wave sources of different orders are proposed to be the particular solution sources. Here, all particular solution sources are located on only one point inside the vibrating body, so the problem of the locations of the particular solution sources is thoroughly solved, and such particular solution sources that are useless for the calculation results are discarded. The theoretical model is established at first, and then the proposed method is used to realize the nearfield acoustic holography (NAH). Subsequently, an experiment is investigated to validate the feasibility and correctness of the proposed method and its application to acoustic holography.     

Resolution enhancement of nearfield acoustic holography by interpolation using band-limited signal restoration method

A new method based on interpolation using band-limited signal restoration method was proposed for enhancing the resolution of the nearfield acoustic holography. According to the band-limited property of the pressure on the hologram surface, a band-limited signal restoration method named Papoulis-Gerchbarg algorithm was used to realize the interpolation of acoustic pressure. Therefore acoustic pressure data on the hologram surface were increased, the sampling interval was reduced, the Information on evanescent waves which was lost because of the large sampling interval was partially recovered, and the resolution of nearfield acoustic holography image was improved. The experimental result shows that the method can enhance the resolution of the nearfield acoustic holography Image efficiently.     

基于径向积分边界单元法的内场声学分析

由于Helmholtz方程的基本解是频率的函数,传统边界单元法在处理声场特征值问题时具有天生的缺陷.采用Laplace方程基本解生成积分方程,通过径向积分法将在此过程中产生的域积分项转化为边界积分.此方法克服了传统边界单元法系数矩阵对频率的依赖,同时克服了特解积分法和双重互易法对特解的依赖,将内场声学特征值问题转化为广义特征值问题.最后通过内场声辐射分析和声学特征值分析验证了算法的有效性.     

芯板垂向可压缩夹层板有限元建模及声辐射性能分析

针对以往夹层板理论大多忽略芯板的垂向应变这一不足,构造了一种考虑芯板垂向可压缩变形的夹层板位移模式,并推导了相应的有限元单元及控制方程,求解了夹层板动力响应,进而利用有限元结果通过边界元法求解了一定频率范围内的夹层板声辐射功率,分析了芯板几何物理参数对夹层板声辐射性能的影响.结果表明,考虑芯板垂向可压缩变形在夹层板声辐射性能研究中是合理的,也是必要的;在一定范围内增加芯板厚度、降低其弹性模量均可减小夹层板单点简谐激励下的声辐射水平.     

深水中复合材料椭圆柱壳声辐射的数值分析

用有限元／边界元法分析深水中复合材料椭圆柱壳的声辐射．首先利用有限元分析壳体的受迫振动,然后提取壳体表面（耦合面）数据,作为声场分析的边界条件,并计及流-固耦合作用,从而可用边界元计算壳体的辐射功率以及壳体表面、近场和远场声压,结果表明系统的耦合振动模态对于其辐射声场具有重要影响．     

快速多极边界元方法在二维声散射问题中的应用

快速多极算法(FMM)是求解边界元方法(BEM)在大尺度情况下的一种非常有效的算法.研究了快速多极算法在二维声散射问题的边界积分方程求解中的应用.给出了积分核函数以及其共轭积分算子核函数的多极展开式,局部展开式以及相应展开系数之间的转化关系.分别应用两种不同的层级树结构的FMM来进行求解,并对两种树结构下的求解效率进行了对比.数值算例表明用快速多极算法求解该问题时在存储量和计算量上比直接求解方法效率更高.