敷设覆盖层的弯曲弹性壳体声散射特性和声振机理研究

As one of the prior researches in underwater acoustics, the sound field prediction of underwater structures has drawn growing concerns. The studies of acoustic scattering characteristics and vibro-acoustic mechanism of curved shells covered with coating layer can provide theoretical basis for the acoustic design of underwater vehicle and coating layer. A lot of work has been done to analyze the acoustic properties of underwater periodic structure which can expand along the plane based on the finite element method combined with the Bloch-Floquet theorem. Nevertheless, underwater vehicles usually have curved shells. This project plans to carry out a research by putting forward a new numerical algorithm and experiments to investigate the acoustic scattering characteristics and vibro-acoustic mechanism of curved elastic shells covered with periodic coating layer. Firstly, the concept of global acoustic impedance will be proposed and the matrix of global acoustic impedance calculated. With the acoustic boundary element method the influence of structure parameters on the acoustic scattering properties will be investigated, it will promote a new way for the analysis of acoustic scattering mechanism. In the meantime, a numerical algorithm will be designed to analyze the periodic cell which expands along a curved surface. With the application of this algorithm, the vibro-acoustic properties of the coating layer and the near-field echo mechanism of the target object can be investigated. Then, an experimental study of the scattered sound field will be carried out and the corresponding theoretical interpretation will be drawn to explore the influence of the coating parameters and the curved shell parameters on the acoustic scattering of the target structure. In this way, we can obtain a new mechanism and understanding of the acoustic characteristics of the curved shell coated with coating layer.

水下结构的声场预测是水下声学研究的重要方向。研究敷设覆盖层的弯曲弹性壳体的声散射特性和声振机理，可以为水下航行器和覆盖层的声学性能设计提供理论支撑。基于Bloch-Floquet理论和有限元方法，已有许多工作描述了可沿平面展开的周期性结构的声学性能。水下航行器的壳体通常为弯曲形状，本项目设计数值算法和实验对敷设覆盖层的弯曲弹性壳体的声散射特性和声振机理进行研究。首先，提出全局声阻抗的概念并对全局声阻抗矩阵进行求解，结合声学边界元法分析结构参数对声散射特性的影响规律，为声散射机理的探索提供新思路；期间，根据求解的模型设计周期单元沿曲面展开的数值算法，并对覆盖层的声振性能和目标结构的近场回声机理进行研究；然后，对散射声场开展实验研究，并发展对应的理论解释，探索覆盖层参数和弯曲壳体参数对目标结构散射声压的影响规律，以获取弯曲壳体覆盖层声学特性的新机理和新认识。

声阻抗是水下结构声场预测的重要边界条件。研究敷设覆盖层的弯曲弹性壳体的声阻抗边界特性，可以为水下航行器和覆盖层的声学性能设计提供理论支撑。本项目对弹性球壳以及弹性和粘弹性复合球壳的声阻抗边界进行研究，提出了全局声阻抗的概念并对全局声阻抗矩阵进行求解和分析。声学边界元方法结合全局声阻抗矩阵求解了球壳结构的声散射目标强度，并指出了局部阻抗求解声学目标强度的局限性。本项目首次提出了全局声阻抗的概念，其包含了整个结构外表面的阻抗元素，是对结构阻抗边界的完整表达，对水下航行器声学性能设计具有重要指导意义。