In shallow water acoustical environment, the propagation of radiated noise of complex structure is determined by the frequency responding properties, spatial directivity, seabed acoustic absorption and the stratification of the sound speed of water. Therefore, it is difficult to assess the propagated noise of complex structure in ocean acoustic environment. In this study, a shaft-hull system (SHS) is established based on the Suboff submarine, the coupled finite element / boundary element (FE/BE) method is adopted to acquire the source strength distribution of the structure, the ray-normal mode theory is used to obtain the sound field Green function in shallow waters, and the closed virtual impedance surface (CVIS) method is employed to eliminate the irregular frequency. On these bases, the radiated sound intensity level (SIL) is decomposed according to the coupling pattern of dry structural modes and sound field normal modes, and the smooth average sound energy is extracted of the radiated noise. It is found that: (1) the non-dimensional irregular frequency of Suboff hull can be estimated with fair precision with reference to the analytical expression of the irregular frequency of slender cylindrical shell (SCS) because the main structure of Suboff is an SCS; (2) the decaying smooth average properties of complex structures can be obtained by only considering the incoherent energy induced by identical sound field normal mode; (3) the far field decaying pattern of complicated structures is approximately similar to that of a monopole source in shallow sea with a soft seabed.

中文翻译：

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浅海轴-船体系统振动声辐射的平滑平均特性


在浅水声环境中，复杂结构辐射噪声的传播是由水的频率响应特性、空间方向性、海底吸声和声速分层决定的。因此，评估复杂结构在海洋声学环境中的传播噪声是很困难的。本研究基于Suboff潜艇建立轴-壳系统（SHS），采用耦合有限元/边界元（FE/BE）方法获取结构的源强度分布、射线法向模态利用理论获得浅水域声场格林函数，并采用闭合虚拟阻抗面(CVIS)方法消除不规则频率。在此基础上，根据干结构模态与声场简正模态的耦合模式对辐射声强级（SIL）进行分解，提取辐射噪声的平滑平均声能。结果表明：(1)由于Suboff船体的主体结构是SCS，因此参照细长圆柱壳(SCS)不规则频率的解析表达式，可以较准确地估计Suboff船体的无量纲不规则频率； (2)仅考虑相同声场简正模引起的非相干能量即可得到复杂结构的衰减平滑平均特性； (3)复杂结构的远场衰减模式与软海床浅海单极源的远场衰减模式大致相似。