含损伤加筋板结构辐射声功率及指向性变异研究

Study on the variations of acoustic radiation power and directivity of a damaged stiffened panel

本文采用结构声振特性中常用参数辐射声功率和辐射指向性来研究含损伤加筋结构的声辐射特性,计算不同加筋情况和结构不同损伤情况下的辐射声功率和远场指向性。基于Mindlin理论,建立描述健康和损伤的四结点有限元板壳单元模型,采用有限元方法计算结构表面动力响应。针对各向同性损伤单元,采取刚度各向整体弱化的方法分析;对于各向异性损伤单元,采用Kachanov理论,引入了x和y两个方向的弹性损伤折减系数。根据Rayleigh积分可以计算结构振动向外辐射的声压,进而可以得到辐射声功率和辐射指向性。考虑到不同损伤存在形式,计算分析了损伤对振动频率、模态以及辐射声功率和指向性的影响。文章建立了一种含损结构的分析方法,通过对一些典型算例分析,在评价损伤对船舶与海洋结构物常用的加筋结构声辐射特性影响方面做出了一定的探索。

Panels are widely used in ship and ocean structures. This paper is concerned with assessing the influences of the damages present in a stiffened panel on its acoustic radiation properties.Acoustic radia- tion power and directivity are two indices, which are able to fully describe the inherence acoustic radiation properties of a linear structure. The sound power and directivity pattern of a stiffened panel under different damaged conditions are thus investigated. Using Mindlin theory, the four-node health and damage shell finite elements were built up, and then the finite element method was applied to calculating the dynamic response of a structure. Isotropic damage elements are built by global and isotropical weakening of the stiffness. Anisotropic damage elements are built by using reduction coefficients for elasticity damages in x and y directions based on Kachanov＇s theory. Sound pressure of structure radiating outwards can be calculated through Rayleigh＇s integral formula,by use of which the radiated power and directivity can then be obtained. Influences of various types of damages on natural frequencies, vibration modes, acoustic radiation power and directivity of sound are studied. Finally, a computational method is given to analyze acousticbehavior of a damaged structure, demonstrated by some typical examples.