The diffraction of sound by an impedance sphere in the vicinity of a ground surface.
The diffraction of sound by an impedance sphere in the vicinity of a ground surface.
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DOI：
10.1121/1.1628681
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发表时间：
2004
期刊：
影响因子：
--
通讯作者：
K. Li;W. Lui;G. Frommer
中科院分区：
文献类型：
--
作者：
K. Li;W. Lui;G. Frommer
本文研究了点声源引起的吸声球的声衍射问题。将理论模型扩展到考虑有限阻抗室外地面上局部反应边界或扩展反应边界的吸声球的声衍射情况。采用分离变量技术和适当的波场展开法，得到了解析解。通过采用镜像方法，可以制定解决方案，以考虑在平坦的声学硬或阻抗地面附近的球体和其镜像之间的声音的多次散射。通过采用称为Weyl-van der Pol公式的近似解析解，将地面对反射声场的影响纳入理论模型中。提出了一种近似解，由一组线性耦合的复方程组确定离地面不太近的吸波球的散射系数。近似方法大大减少了计算声场的计算时间。对开孔聚氨酯泡沫吸声球的声学性能进行了初步的测试。随后进行了实验，以证明所提出的理论模型的有效性，为各种源/接收器配置周围的球以上的声学硬地面和阻抗地面。理论预测与实验结果进行了比较，结果令人满意。结果表明，由近似解得到的理论预测与用精确解得到的结果吻合得很好。
The problem of sound diffraction by an absorbing sphere due to a monopole point source was investigated. The theoretical models were extended to consider the case of sound diffraction by an absorbing sphere with a locally reacting boundary or an extended reaction boundary placed above an outdoor ground surface of finite impedance. The separation of variables techniques and appropriate wave field expansions were used to derive the analytical solutions. By adopting an image method, the solutions could be formulated to account for the multiple scattering of sound between the sphere and its image near a flat acoustically hard or an impedance ground. The effect of ground on the reflected sound fields was incorporated in the theoretical model by employing an approximate analytical solution known as the Weyl-van der Pol formula. An approximation solution was suggested to determine the scattering coefficients from a set of linearly coupled complex equations for an absorbing sphere not too close to the ground. The approximate method substantially reduced the computational time for calculating the sound field. Preliminary measurements were conducted to characterize the acoustical properties of an absorbing sphere made of open cell polyurethane foam. Subsequent experiments were carried out to demonstrate the validity of the proposed theoretical models for various source/receiver configurations around the sphere above an acoustically hard ground and an impedance ground. Satisfactory comparative results were obtained between the theoretical predictions and experimental data. It was found that the theoretical predictions derived from the approximate solution agreed well with the results obtained by using the exact solutions.