Research On The Analysis Of Interior Sound Field In Enclosure Based On Panel Acoustic Contribution

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.