【作者】 姜琳；

【导师】 赵德有；

【作者基本信息】 大连理工大学 ， 船舶与海洋结构物设计制造， 2008， 博士

【摘要】 随着科学技术的发展,近几十年来结构体的声散射一直受到许多工程领域的重视。结构体的声散射含有结构物的几何形状以及结构组成等重要的信息,通过对散射波场的分析,可以实现对结构物的侦测以及探伤,深入研究目标的散射特性是实现目标特征提取和识别的基础,因此,声散射的研究在实际工程中有十分重要的应用价值。本文对船舶与海洋结构物中的板壳等结构的声散射作了数值和实验分析,完成的主要工作和创新性成果如下:基于Greenberg的方法,推导了具有阻抗边界条件的浅水Green函数。建立了浅水域的声学边界元方程,利用边界元法研究了三维海洋波导与散射体相互作用的问题。分析了当声波与结构体相互作用时,理想边界条件以及海底阻抗对结构散射特性的影响。数值分析表明:浅海中椭球体的散射特性与自由场中明显不同,当椭球体按照一定比例变化,其散射声压变化规律会近似于球体而声压幅值低于球体。具有阻抗边界条件的浅海球体的散射特性与理想海底差别较大,海底阻抗对水平断面以及垂直断面的散射场都有一定的影响,目标距离海底越近,计算场点散射声压受海底边界条件的影响越大,阻抗越大,散射声压越大。分析浅海声散射时,海底阻抗的影响不可忽视。合理设计水下结构,控制其在浅水域中散射特性是未来研究发展的方向。利用边界元法,对刚性和绝软表面裂纹板的声散射进行了数值分析。考察了裂纹的位置以及形状等因素对散射声压影响。计算结果表明,裂纹数目越多,散射声压越低;含裂纹的刚性板和绝软板对声场的指向性影响较大。其次,采用先进的声学测量系统对包括直裂纹、斜裂纹、表面裂纹、不同裂纹类型组合的多裂纹板等13块边界为自由边界的铝板以及完好板进行了插入损失试验分析。试验结果表明:裂纹长度和裂纹板的插入损失成反比。裂纹越长,插入损失越小;裂纹距离声源越近,插入损失越小;裂纹越深,插入损失越小;裂纹数量越多,插入损失越小。插入损失可以作为一种诊断指标应用于无损检测当中。利用简单的实验装置将球形声源近似为点声源,以敷设阻尼和软表面材料的铝板为研究对象,利用声学测量系统,考察了在点声源作用下铝板的声散射以及声透射特性。实验结果表明:在点声源作用下,有限板的声透射特点是声源距离有限板越近,插入损失越大,敷设阻尼有限板的插入损失要比没有敷设阻尼有限板的大,敷设软表面材料板的插入损失要高于普通铝板的插入损失。因此,在船舶含有声源的舱室内敷设阻尼(或者敷设相对较“软”材料),能够起到更好的隔声效果,提高舱室内部声源向声场中透射的传声损失。本文的研究结果在研究敷设阻尼结构的声散射、声透射等方面有着积极作用,对于预报潜艇的振动、噪声和提高潜艇的声隐身性能有着重要意义。更多还原

【Abstract】 With development of scientific technology, acoustic scattering by object has been a topic of interest over the past few decades. The importance of studying the acoustic scattering by objects lies in the fact that many physical objects can at least be approximated by one of the aforementioned geometries or non-destructive detection. The object acoustic scattering characteristic is the basic of target identification that is so significance to study. This dissertation addresses a detailed of studying on numerical and experimental of plane and shell acoustic scattering characteristics for ship and offshore structure. The major contributions and conclusions are as follows:A new shallow water Green’s function for sea bottom with impedance boundary condition is derived. The interaction of acoustic wave with the scattering ellipsoids object in an ocean wave-guide was examined by using BEM. The effect of impedance boundary on the scattering characteristics of the acoustic wave by an obstacle was considered and the results show that the scattering characteristic of ellipsoids in shallow water is different from that of in infinite field. The scattering pressure made by ellipsoids is not only similar but also lower than that of sphere when the ellipsoids scale is appropriate. The scattering characteristic of ellipsoids in shallow water with impedance boundary condition is different from that of rigid sea bottom. The impedance boundary condition affects both the horizontal propagation and vertical propagation greatly. The scattering pressure will greatly increase if the object is close to sea bottom or the impedance is large. The effect of impedance boundary condition on scattering characteristic by an obstacle in shallow water wave-guide is prominent Design the dimension scale of underwater structures reasonable and control its scattering characteristics will be further developed.The acoustic scattering characteristics of a three-dimensional finite plate with multi-cracks considering both soft and rigid surface conditions are studied by using BEM. The effect of the cracked position and the shape of the crack on scattering pressure are considered. It is can be concluded the sound pressure decrease as the cracks increasing and the diversification of sound pressure and directivity of pattern are greatly effect by the hard plane and the soft surface plate with cracks. The correlation acoustic scattering and transmission experiments of 13 freedom plates of different cracks and an intact freedom plate have been investigated by using advanced acoustical experiment system. Insertion loss is used as diagnose index and experimental show that insertion loss is sensitive to the crack position and it will be decreasing with the length, the depth and the number of cracks. Insertion loss can be considered as an easy new diagnose index for non-destructive detection.The correlation acoustic scattering and transmission experiment of damped finite plate has been investigated in this paper by using advanced acoustical experiment system that the sphere source is changed to plane sound beam. Experiment results show that the insertion loss increases greatly as the distance between sound source and finite plate becomes closer. The insertion loss made by the damped plate is higher than that made by non-damped plate and the effect of sound insulation made by soft surface plate facing to source is better than the non-damped plate. It can be concluded that the damped layer and soft surface have a better effect on acoustic isolation and enhance transmission loss if the damped layer or soft surface is placed inside of the cabin of the ship. Besides, study the acoustic scattering and sound transmission is especially important for the prediction of vibration and noise and the design of sound-absorbing layer and the safety of submarines.更多还原