嵌入周期性信号调节板的弹性覆盖层结构的水声学特性研究

Attaching compliant coating is a common means to suppress the flank array mechanical noise. This compliant coating, however，can greatly degrade the signal received by the hydrophone array placed in front of the coating surface. Traditional way of fully covering a signal conditioning plate (SCP) on the coating surface has limited effect of reducing the signal degradation and also makes the structure unnecessarily heavy. Based on the embedded and periodic characteristics of the actual flank array hydrophone, this project proposes partially attaching or embedding periodic SCPs’ array on the surface of and inside the coating, in an effort to reduce the weight of the structure and to further enhance local reflection and signal gain at each SCP via taking advantage of the multi-mode locally resonant characteristics of each SCP and of the diffraction, scattering and coupling effects of the structural and acoustic waves by the periodicity of structure. The effect of these resonant characteristics and wave effect on sound radiation and absorption characteristic of the coated structure is also to be studied. The underwater acoustic and vibro-acoustic-coupling characteristics of three cases are designed to be investigated: 1) coated plate attached with periodic SCPs, 2) coated plate with an embedded SCP, and 3) coated plate with embedded and periodic SCPs. Though analytical modelling, numerical simulations and experiment, this project aims to achieve multiple goals of increasing signal gain of the hydrophone array, increasing surface absorption of the coated structure, and reducing its radiation of sound. The research result from this project can provide scientific basis and support for the new underwater coating design and optimization.

敷设柔性覆盖层是降低舷侧阵机械噪声的常用手段。然而该覆盖层对放置其上的水听器阵拾取的声信号有较大衰减。传统覆盖层表面完全敷设信号调节板的方式对减少信号衰减作用有限且结构笨重。本项目根据实际中舷侧水听器阵模制在弹性层内及周期性的特点，提出弹性覆盖层表面局部敷设或内嵌周期性信号调节板，在减轻结构重量同时，利用有限宽信号调节板多模态局部共振特征及周期性结构对结构波和声波的绕射、散射及耦合效应，进一步提高各板表面声反射和信号增益。同时研究这些共振特征和波动效应对覆盖层结构声辐射和声吸收的影响。拟通过解析建模、数值仿真和试验手段，研究声、力源激励下，覆盖层板结构1)表面敷设周期性信号调节板; 2)内嵌单块信号调节板; 3)内嵌周期性信号调节板三种情形下的水声学及声振耦合特性，实现增加水听器阵增益及结构表面声吸收、减小结构声辐射的多重目标，为新型水下覆盖层结构优化设计提供科学依据和支撑。

本项目针对现有舷侧阵水听器覆盖层结构的水声学性能中存在的几个关键性难题，即信号增益衰减问题及平台噪声问题，分别研究了声、力源激励下，覆盖层板结构：1)表面敷设周期性信号调节板; 2)内嵌单块信号调节板; 3)内嵌周期性信号调节板三种情形下的水声学及声振耦合特性。利用有限尺寸信号调节板多模态局部共振特征及周期性结构对结构波和声波的绕射、散射及耦合效应，进一步提高了各板表面声反射和信号增益，并同时改善了结构表面吸声性能及抑制噪声辐射。研究结果显示，1）SCP周期性敷设在覆盖层表面可引起SCP所在区域局部声反射在较宽频带的显著提高，同时对表面声吸收影响较小，在低频还可引起声吸收的显著增加；2）表面敷设SCP可同时引起覆盖层弹性板结构在阻带振动的局域化及相应声辐射的增加；增加覆盖层厚度、减小其密度、纵波声速、增加其阻尼损耗因子、减小SCP相对尺寸等可削弱SCP引起的振动及声辐射；3）将单个SCP内嵌于覆盖层内激励源的上方比表面敷设SCP时声辐射功率在整个底板吻合频率下显著降低；除了低频在两个离散的弹簧质量频率处增加；4）将SCP内嵌于两层覆盖层之间可显著增加结构表面声吸收，同时可极大改善SCP附近的信号响应/增益。并通过进一步的参数分析和优化提出可同时达成增加水听器阵增益及结构表面声吸收、减小结构声辐射的多重目标，为新型水下覆盖层结构优化设计提供科学依据和支撑。