【作者】 王斌；

【导师】 汤渭霖；

【作者基本信息】 上海交通大学 ， 水声工程， 2008， 博士

【摘要】 水下结构辐射噪声预报是水声领域一项重要研究内容,是定量声学设计、减振降噪设计等工作的理论基础与重要依据。对于潜艇这类大型水下结构而言,辐射噪声的实时监测或者快速预报是提高其战斗力与生存力的有力保障。因此,辐射声场预报研究具有重要的理论价值和广泛的应用背景。本文以大型结构辐射噪声的快速预报为目标,遵循理论研究和工程应用相结合的研究思路,开展了辐射声场快速预报的理论与试验研究。深入分析了表面振动与辐射声场之间的传递规律,声场声压等于表面振速向量与声传递向量的内积,声传递向量的元素等于与辐射面共形的刚性障板表面对应活塞以单位速度振动时的辐射声压。讨论了以规则障板表面活塞辐射声场近似实际障板表面活塞辐射声场的合理性。对于实际障板尺度远小于或者远大于声波波长的情况,其表面活塞的辐射可以分别看作点声源或者平面波的辐射。即便规则障板与实际障板拟合程度不高,拟合前后表面活塞的辐射声场差别很小。对于实际障板尺度与声波波长可比拟的情况,其表面活塞的辐射声场主要取决于以活塞为中心、尺度与声波波长相当的局部障板形状,规则障板与该局部障板的拟合程度决定了声场预报精度。只要保证对辐射声场起主要贡献的单元所对应的声传递向量元素是准确的,便可以较好地近似总辐射声场。最终,建立了一个具有坚实理论基础、可应用于大型水下结构辐射噪声快速预报的理论算法——单元辐射叠加法。该方法没有非唯一性、奇异积分以及高维矩阵求逆等问题的困扰,计算速度远远高于边界元等其它数值积分方法。一系列算例表明,该方法的计算结果从甚低频直至高频均与解析数值解或者边界元结果符合得很好。从理论上分析了平面、圆柱面两类典型辐射面表面振动空间采样所引起的声场预报误差问题。将平面、圆柱面振速分布分别变换到二维波数域或者轴向、周向波数域,建立变换谱与辐射声场之间的对应关系,再根据空间采样后变换谱的混叠程度确定辐射声场的预报误差。对于固定观察方位与分析频率,平面辐射面声场预报精度是由空间采样前、后表面振速的二维波数谱在特定波数上的比值决定的;圆柱辐射面声场预报精度是由空间采样前、后表面振速的轴向、周向波数谱在特定轴向波数上、特定周向波数范围内的比值决定的。数值分析了简支矩形板、简支圆柱壳表面振动空间采样间隔与辐射声场预报误差之间的关系,并将有关结论推广到一般矩形板、圆柱壳表面振动空间采样情况。与国内有关单位联合开展了水下多舱段壳体结构振动声辐射的试验研究。针对试验中出现的振动相位信息缺失情况讨论了辐射噪声的工程预报问题,因为这种情况具有实际意义。根据声场叠加原理,将辐射声压级表示为表面单元独立振动时辐射声压级与修正因子之和的形式,其中修正因子反映了由于表面振动的相位关系引起的辐射声压相关性。再通过理论和试验研究,分析了修正因子与观察距离、表面振速插值密度等因素之间的关系。对于距离足够远的同一观察方位而言,修正因子与测量距离无关;随着表面插值、细化单元的增多,修正因子相应增大。在此基础上,提出了一种基于特定工况修正因子预报其它工况辐射噪声的工程预报方法。对于在工作频段或者源强度上可以区分的多台设备激励情况,根据设备全开工况的修正因子可以预报其它工况的辐射噪声;对于多台设备在工作频段、强度上无法区分的情况,根据特定工况的修正因子在某些频率范围内可以预报其它工况的辐射噪声。本文对表面振动与辐射声场之间传递规律进行了较深入的理解和阐述。提出了一种新的辐射声场预报方法,适用于大型水下结构辐射噪声的快速预报,为定量声学设计或者减振降噪控制提供了新的理论依据。从空间信号的离散与重建角度,分析了表面振动空间采样与辐射声场预报精度之间的关系,对于表面振动测点布放方案的设计与评估具有一定指导意义。讨论了表面振动相位信息未知情况下辐射噪声预报的试验修正方法,为解决辐射噪声工程预报中实际问题提供了新思路。更多还原

【Abstract】 The prediction of noise radiated by underwater structures is one of the most important research contents in the field of underwater acoustics. It is regarded as the theoretical foundation and the important criterion for quantitative acoustic design and vibration-noise control. For the large underwater structures such as submarines, fast prediction or real-time monitoring of noise is crucial in improving the fighting and survival capacities. Therefore, the research on prediction of noise radiated by underwater structures has important theoretical value and wide engineering application. In this dissertation, fast prediction of noise radiated by large underwater structures is focused on. Theoretical and experimental investigations are implemented following the principle of theoretical research combined with engineering application.The physical essence of transfer law between the surface vibration and the acoustic field has been analyzed deeply. The acoustic pressure equals the inner product of two vectors, namely, surface velocity vector and Acoustic Transfer Vector (ATV). The element of ATV equals the acoustic pressure radiated by the corresponding piston vibrating in unit speed on the rigid baffle coinciding with the vibrating surface. The discussion is focused on the rationality of the acoustic pressure radiated by the piston on the actual baffle approximated by the analytical solution of that on the regular baffle. In the case of the dimension of the actual baffle far larger or less than the acoustic wavelength, the radiation of the piston can be regarded as that of a point source or a planar wave, respectively. Although the regular baffle does not fit the actual baffle well, the difference of the acoustic pressure radiated by the piston before and after fitting can be ignored. In the case of the dimension of the actual baffle comparable with the acoustic wavelength, the acoustic pressure is mainly determined by the shape of the neighboring baffle on the acoustic wavelength scale. The error is mainly determined by the fitting degree between the regular baffle and the actual baffle. As long as the elements of ATV dominating the whole acoustic pressure are accurate, a satisfying prediction can be obtained. Finally, a method named Element Radiation Superposition Method (ERSM) is established which has profound theoretical foundation and can be applied to the fast prediction of noise radiated by large underwater structures. It succeeds to avoid the problems of non-uniqueness, singularity integral and high-dimensional matrix inverse. Consequently, it has a larger advantage in calculating speed than the numerical integration methods. A series of numerical analysis prove that the results of ERSM are in satisfactory agreement with those of analytical solutions or BEM either in low frequency or in high frequency.The relationships between the prediction precision of acoustic pressure and the spatial sampling interval on surface vibration are analyzed theoretically for two typical surfaces, namely, plane and cylinder. The distributions of surface vibration are transformed to two-dimensional wavenumber domain or axial circumferential wavenumber domain respectively. The mappings between the transformed spectrums and the acoustic pressures are established. The prediction error is totally determined by the degree of aliasing in the corresponding transformed domains resulted from spatial sampling. For the fixed observed bearing and analyzing frequency, the prediction precision of acoustic pressure radiated by a vibrating plane is determined by the ratio of the two-dimensional wavenumber spectrums at the specific wavenumber before and after spatial sampling. The prediction precision of acoustic pressure radiated by a vibrating cylinder is mainly decided by the ratio of the axial circumferential wavenumber spectrums at the specific axial wavenumber and below the specific circumferential wavenumber before and after spatial sampling. The spatial sampling interval required by the designated acoustic pressure prediction precision on the simply supported rectangular plate and that on the simply supported cylindrical shell are analyzed numerically. Some conclusions are extended to the cases of spatial sampling on the generally supported rectangular plate and that on the generally supported cylindrical shell.Experimental research on vibration and radiation of underwater multi-compartmented shell structure is performed together with the related Institute. An engineering method of noise prediction is discussed to solve the problem of vibration phase missing in this experiment. According to the superposition principle of acoustic field, the acoustic pressure level can be expressed as the sum of the acoustic pressure level radiated by the surface elements vibrating independently and a modifying factor. Therein, the modifying factor reflects the correlation between the acoustic pressures arising from the phase inconsistency of the surface vibration. Through the theoretical and experimental studies, the influences of the observation distance and the surface vibration interpolation degree on the modifying factor are analyzed. For the far observers in the same bearing, the modifying factor has nothing with the observation distance and increases with the number of surface elements in the interpolation process. On the basis, an engineering method is put forward to predicting the noise with the modifying factor obtained in the specific case. If the vibration equipments work in different frequency or in different intensity, the noise can be predicted by the modifying factor obtained in the case of all vibration equipments working. If not, the noise can be predicted in some frequency band by the modifying factor obtained in the specific case.The study in this dissertation provides some further understanding on the rule between vibration and radiation. A new method is put forward to predicting the noise radiated by large underwater structures and providing theoretical foundation for quantitative acoustic design and vibration-noise control. In view of the sampling and reconstruction of spatial signal, the relationships between the spatial sampling on surface vibration and the prediction error of acoustic pressure are analyzed. Some conclusions are of certain guiding significance in designing and evaluating the laying scheme of surface vibration measurements. The prediction method in the case of vibration phase missing has been discussed and provides a new way to solve the actual problems in engineering noise prediction.更多还原