敷设分层梯度声学覆盖层的加肋圆柱壳声辐射特性研究

Sound radiation characteristics of ribbed cylindrical shells with multilayer graded acoustical coating

单壳体潜艇敷设声学覆盖层应具有机械噪声、水动力噪声和声目标强度控制的多功能特性,为此需要解决两个基本问题:其一,提高机械噪声低频控制效果;其二,实现覆盖层的多功能兼容性。本文从降低机械激励壳体声辐射角度出发,采用模态叠加法,建立无限大理想水介质中分层梯度声学覆盖层与有限长加肋圆柱壳的声振耦合及声辐射模型,基于声学覆盖层模态传递函数特性,计算分析声学覆盖层分层梯度分布及厚度、层数等参数对加肋圆柱壳辐射噪声影响的特征和规律,给出分层梯度声学覆盖层的特征声阻抗渐变参数分布并与敷设均匀声学覆盖层降噪特性比较。研究结果表明:加肋圆柱壳敷设内层至外层声阻抗逐渐递增,各分层取慢波速的声学覆盖层,具有比均匀声学覆盖层更有效地降低外表面振动位移的特性,可明显增加降噪效果,并扩展低频降噪范围。声学覆盖层的优化应增加声阻抗的内分层失配和外分层适配的效应,有利于降低加肋圆柱壳低频声辐射,并可兼顾降低声目标强度。

Mono-shell submarine's acoustical coating is supposed to possess the multifunctional characteris⁃tics of mechanical noise,hydrodynamic noise and acoustic target intensity control.Two difficulties need to be addressed for this purpose:the first one is to improve the mechanical noise low-frequency control effect;the other one is to achieve multifunctional compatibility of acoustical coating.In this paper,from the perspective of reducing the sound radiation of mechanically excited shells,modal superposition method was adopted to establish the vibro-acoustic coupling and sound radiation model of multilayer graded acoustical coating and finite length ribbed cylindrical shell in ideal aqueous medium of infinite size.Based on the acoustic coating modal transfer function characteristics,the acoustic coating gradient distribution characteristics,thickness,the number of layers and other parameters were analyzed to reduce sound radiation of the ribbed cylindrical shell.The characteristic acoustic impedance asymptotic parameter distribution of the layered gradient acous⁃tic cover was given and compared with the sound reduction characteristics of laying a uniform acoustic cover.The results indicate that the acoustic coating with increased acoustic impedance and slow wave velocity from the inner to the outer layer of the ribbed cylindrical shell has the property of reducing the vibration displace⁃ment of the outer surface more effectively than the uniform coating,which can significantly increase the sound reduction effect and extend the low frequency range of noise reduction.Optimisation of the acoustic coating should increase the acoustic impedance mismatch of the inner layer and the outer layer adaption ef⁃fect,in order to help reduce the low frequency acoustic radiation of the ribbed cylindrical shell and to take the reduction of the acoustic target intensity into account.