【作者】 肖悦；

【导师】 陈剑；

【作者基本信息】 合肥工业大学 ， 车辆工程， 2014， 博士

【摘要】 弹性封闭空腔结构在动态载荷激励下产生振动进而形成的空间复杂声场是工程实际中最具代表性的一类声场，如汽车、船舶和飞机的舱内声场。对该类声场的研究一直以来都是振动与噪声控制领域的一个重要研究方向，实现对这类封闭空腔结构内部声场的声学响应预测和分析，具有重要的理论研究意义和广阔的工程应用前景。根据传递路径分析方法的原理，系统响应可认为是外界激励通过多种不同路径传递到响应点的能量贡献叠加。因此通过识别外界激励载荷和计算结构振动声辐射来解决复杂封闭空腔结构的振动噪声分析与控制问题。本文以封闭空腔结构受激所形成的内部复杂声场为研究对象，用结构部件的面板声学贡献度代替先前的传递路径贡献量，以预测和控制封闭结构声腔内的声学响应为目标，深入研究结构外界激励载荷的识别和复杂封闭空腔内部声场响应计算两个关键问题。在激励载荷的识别方面，提出了具有一般意义的结构动态载荷时域识别方法，提高了载荷识别的精度和稳定性。在振动声辐射计算求解方面，提出了用于计算复杂封闭结构振动形成的内部空间声场的等效声传递向量法，避免了边界元法的固有缺点，计算效率更高。在封闭空腔结构内声场预测和声学优化方面，提出了一种基于等效源法的内部近场声全息的面板声学贡献度计算方法，该方法可在重建封闭空腔结构内声场的同时，有效识别出各振动板件对封闭声场的声学贡献度。完成的主要研究工作和成果如下：（1）阐述了封闭空腔结构内部声场分析的研究意义，详细回顾了动态载荷识别方法和封闭空腔结构内部声场计算的研究现状和进展，分析了其中仍然存在的一些值得研究的问题，并以此为基础，确定了本论文所要研究的主要内容。（2）针对响应中带有噪音时载荷识别的困难，提出了联合奇异熵去噪修正和正则化预优的共轭梯度迭代识别方法。系统的振动响应表示为单位脉冲响应函数与激励载荷的卷积，并离散化一组线性方程组，将载荷识别问题即转化为求解线性方程组的反问题。一方面对含噪信号进行基于奇异熵的去噪处理，提高反问题求解中输入数据的精度。另一方面利用正则化方法对共轭梯度迭代算法进行预优，改善反问题的非适定性。由于从输入的响应数据去噪和正则化算法两方面同时改善动态载荷识别反问题的求解，因此可以有效地抑制噪声，提高识别精度。通过数值算例分析，表明在不同的噪声水平干扰下，其识别精度均优于常规的正则化方法，能够实现有效稳定地识别动态载荷。最后通过实验研究进一步验证了该方法的正确性和有效性。（3）对封闭空腔结构内声场分析计算问题的数值求解方法进行了详细的论述，推导了求解Helmholtz方程的声学有限元法和声学边界元方法的理论公式，并分析了这两种数值计算方法在实际应用中的不足之处。（4）推导了基于边界元法的声传递向量的计算公式。提出了用于分析复杂封闭空腔结构内声场的等效声传递向量法，导出了等效声传递向量和面板声学贡献度的理论公式，研究了等效声传递向量法的数值计算误差影响因素。该方法避免了边界元法中复杂的数值计算和奇异积分的处理过程，简化了计算过程，有利于向工程实际推广。分别以三个不同形状结构形成的声腔模型为例进行声场分析，仿真实验结果证明了该方法的正确性和有效性。（5）基于等效源法的内部声全息技术，提出了一种复杂封闭空腔结构内声场的面板声学贡献度识别方法。首先重构出振动结构表面的法向振速，实现对整个内部封闭声场的预测，再将振动结构的每个面板在腔体内部场点产生的声压分别用位于空腔表面附近的等效源在该点产生的辐射声压代替，将复杂的封闭非自由声场问题转化为简单的内部自由场问题，结合重建出的结构表面法向振速进而识别出封闭振动结构各面板对腔体内任意位置的声学贡献度。研究了等效源的数量及与重建面距离等参数对重建精度的影响，通过复杂结构内声场的数值仿真和实验研究的结果验证了所提方法的正确性和有效性。（6）总结本文的主要研究成果，指出了需要进一步研究和解决的问题。更多还原

【Abstract】 The interior sound field in enclosure such as the cabins of automobiles, ships and airplanes, which is induced by the vibrations due to the external excitation, is the most representative in engineering. The research of this kind of sound field has always been an important aspect of noise and vibration control domains. It has important theory significance and wide engineering application prospects to predict and analyze the acoustic response of the interior sound field in enclosure.According to the principle of transfer path analysis method, the response of the system can be considered as a sum of path contributions that generated by the external excitation through multiple transfer paths. Therefore, for the interior sound field in complex enclosure, identifying the external exciting load and calculating acoustic radiation of structural vibration can be applied to solve the problem of vibration and noise analysis.In this dissertation, the research is focused on complex enclosure and the interior sound field caused by its vibration, which is regarded as a source-path-receiver system. Based on this model, the transfer path contribution is replaced by the panel acoustic contribution of individual structural component. Aiming at prediction and control the acoustic response of the interior sound field in cavity, the identification method of external dynamic load and calculating method of the interior sound field, the two key problems, have been studied in depth to help one judge whether it is a problem of excitation source or the system itself. In order to obtain the strength of external loads, a general method for dynamic force identification in time domain is proposed, which can be used to improve accuracy and stability of load identification. For the analysis of interior sound field in irregular enclosure, a new method called equivalent acoustic transfer vector is developed, which can avoid the shortcomings of BEM and has higher computational efficiency. For obtaining panel acoustic contribution, by using interior nearfield acoustic holography based on equivalent source method, an identification approach of panel acoustic contribution is presented. This method can be applied to realize reconstruction of the interior sound field in enclosure and identification of the acoustic contribution of each panel to any position in the interior sound field. The detailed research contents of this dissertation are summarized as follows:(1) The research significance of the analysis of interior sound field in enclosure has been explicated, and the research state and development of identification of dynamic load and calculation of acoustic radiation of the vibrating structure have been reviewed. Then the problems of the above methods have been analyzed. Finally, the main research contents in this dissertation have been determined based on the literature review.(2) To smooth out the difficulties of the load identification in the presence of noises, a dynamic load identification method is proposed based on the combination of the singular entropy denoising and the regularization-preconditioned conjugate gradient iteration method. The response of the linear system can be obtained by the convolution integral of the unit pulse response function and dynamic loads. Hence, by discretizing the convolution integral into a set of linear algebraic equations, the load identification problem can be transformed into an inverse problem of solution of linear algebraic equations. In order to improve the accuracy of input data in the process of load identification, the singular entropy denoising method is introduced in the noisy response signal. Furthermore, the conjugate gradient iterative algorithm is preconditioned by Tikhonov regularization method to alleviate the ill-posedness of the inverse problem. Since the solution of load identification inverse problem is improved at two respects: the input response data denoising and regularization algorithm, the proposed method can effectively suppress noise and improve the identification accuracy. The numerical simulation result for a given example indicates that the proposed methods are more accurately and stably in the identification of dynamic loads with the interference of different noise levels, compared with the conventional regularization methods. Finally the validity and the effectiveness of the proposed methods are verified by the experiment.(3) The numerical methods for computating the interior sound field in enclosure have been discussed in detail. The theoretical formulas of acoustic finite element method and boundary element method for solving the Helmholtz equation have been derived, and the shortcomings of these two numerical methods in practical application are analyzed.(4) The theoretical formulas for solving acoustic transfer vector based on boundary element method are deduced. Based on these, a method called equivalent acoustic transfer vector for the analysis of sound field in irregular enclosure is developed. The calculation formulas of the equivalent acoustic transfer vector and panel acoustic contribution are deduced. Compared with boundary element method, complicated numerical calculation and the singular integrals are avoided in the proposed method, and the calculation process is simplified. Three simulations are conducted by taking different shaped enclosures for example and the results show that the proposed method is correct and effective.(5) By using interior nearfield acoustic holography based on equivalent source method, an identification approach of panel acoustic contribution is presented. The normal velocities on the surface of vibrating structure have been reconstructed and the interior sound field in enclosure has been predicted. Then the sound pressure produced by each panel at the interested field point is respectively replaced by the radiated pressure of the interior sound field which is formed by the equivalent virtual sources located near the enclosure surface. Combining with the reconstructed normal surface velocities, the acoustic contribution of each panel to any position in enclosure can be obtained by transforming the complex enclosed non-free field into the simple interior free field. The influences of the number of the equivalent sources and the distance between them and the reconstructed surface have been investigated. The numerical simulation and the experiment are used to demonstrate the correctness and validity of this method.(6) Researches in this dissertation have been summarized, and the topics for further study have been proposed.更多还原