Wave Superposition Approach Based Acoustic Holography And Acoustic Sensitivity Analysis

Since noise measurement and control engineering are attracting more and more attentions, near-field acoustic holography (NAH) and acoustic sensitivity analysis have been investigated in this dissertation. Near-field acoustic holography which was proposed in the beginning of 1980s, can reconstruct and predict acoustic quantities such as sound pressure, particle velocity, sound intensity and far-field directivity in the whole 3-D field without the resolution limitation by recording the sound pressure in the near-field of radiator. Because of such special features, the NAH technique becomes one of the most powerful tools to identify sound sources and visualize sound field. Meanwhile, the technique have achieve many progresses in itself, and its implementation algorithms mainly consist of spatial transform of sound field (STSF), boundary element method (BEM) and Helmholtz equation least-square method (HELS). Based on the implementation and enhancement of the STSF-based NAH, sound field separation technique has been proposed in this dissertation. In order to overcome the shortcomings of the BEM and HELS based NAH, wave superposition approach (WSA) based NAH has been proposed and applied to the analysis of interior or exterior sound field. As far as acoustic sensitivity analysis, wave superposition approach (WSA) based acoustic sensitivity analysis has been proposed by differentiating wave superposition formulation with respect to design variables. The main contents in the dissertation are summarized as follows:In chapter one, the history of NAH and acoustic sensitivity analysis has been reviewed, and the current status and problems existed in them have also been analyzed. Then the solutions to these problems have been presented and the main research content has been determined in the dissertation.In chapter two, the STSF-based NAH has been implemented and some problems of it have been solved. The theoretical formula of planar, cylindrical and spherical NAH have been deduced according to special function and variable-separating method. Meanwhile, the numerical algorithm and error transmission have been discussed in this chapter. Finally, an experiment using scanning holographic pressures has been conducted, where a cut-off wave-number determination method has been proposed without prior or post knowledge.In chapter three, sound field separation technique has been proposed, which widen the applicable scope of the STSF-based NAH. According to the NAH theory and propagating characteristics along different directions, sound field separation technique can be established in the wave-number domain. The acoustic quantities on the target source surface and in the field can be reconstructed without the influence ofthe background noise using the separated pressures.In chapter four, the theoretical basis and description to determine solution hasbeen given, and Helmholtz integral equation and its numerical form that is boundary element method have been deduced. Based on these, the basic formulation of WSA has been deduced and its equivalence to BEM has been verified. In the end, the implemented process and precision analysis have been given.In chapter five, the WSA-based NAH has been proposed. According to wave superposition formula, a robust reconstruction method has been established for all wave numbers by introducing hybrid layer potential theory. The ill-posed nature of holographic process and its regularization strategy has been investigated deeply. The correctness of theoretical analysis has been verified through numerical simulations and experiments. In addition, influence of frequency and factitious source position to reconstruction precision has been investigated.In chapter six, wave superposition formulation in cavity has been deduced, and the WSA-based interior NAH and its implementation method using isotropic parameter interpolation have been established. The results of several typical simulations show that the calculated result can coincide with the theoretical values very well after regularization, even if the data including measurement errors is used to reconstruct and predict, and the Tikhonov method can obtain a little bit better effect than the truncated singular value decomposition (TSVD) method.In chapter seven, the 3-D acoustic sensitivity analysis theory and its implementation algorithm have been developed. According to WSA, the relation between acoustic quantities in field and acoustic and spatial parameters on product surface can be established. Then the analytical formulation of acoustic sensitivity analysis can be obtained by differentiating with respect to design parameters. Finally, the calculation equation can be obtained through the discretization of the analytical formulation. Several simulations have been taken to test the feasibility and effectiveness of the WSA-based acoustic sensitivity analysis.In chapter eight, researches in this dissertation have been summarized, and the topics need further study have been proposed.