Investigation On Statistically Optimal And Wave Superposition Methods Based Nearfield Acoustic Holography

Nearfield acoustic holography (NAH) is a powerful tool for identifying noise sources and visualizing acoustic field. By measuring the plural sound pressures on a hologram surface close to the noise sources, the acoustic quantities such as sound pressure, particle velocity and sound intensity at any point in the three-dimensional acoustic field as well as the sound power radiated by sound source can be reconstructed or determined. Firsty, the history of NAH has been reviewed, and the current status and problems to be solved have also been analyzed. In order to overcome the rigid requirement on the measuring size of the hologram surface in the spatial transform of sound field based NAH (STSF based NAH), the statistically optimized method based NAH has been developed. For overcoming the shortcomings of the routine wave superposition approach based NAH (WSA based NAH) in the holographic reconstruction of the coherent acoustic field and the semi-free acoustic field, combined wave superposition approach based NAH and NAH for the semi-free acoustic field have been presented. The dissertation is summarized as follows:In chapter one, the history of NAH has been reviewed, the current status and problems to be solved have also been analyzed. The advantages and disadvantages of different kinds of implementation algorithms of NAH have been analyzed too. Then the solutions to these problems have been presented and the main research content of this dissertation has been determined.In chapter two, the sound field superposition theory is used to prove the formulas of the statistically optimal planar nearfield acoustic holography. A simple and effective method, which is used to choose the wave number vector, is proposed. To overcome the limitation, that sound field on one side of hologram surface must be free, on application of the normal statistically optimal planar nearfield acoustic holography, the sound field separation technique with two hologram surfaces is proposed.In chapter three, statistically optimal cylindrical interior and exterior nearfield acoustic holography have been presented. The acoustic field separation technique of the statistically optimal cylindrical nearfield acoustic holography has also been developed.In chapter foure, the statistically optimized method based NAH has been brought into the spherical coordinates, and the statistically spherical interior and exterior nearfield acoustic holography have been developed. Samely, the acoustic field separation in the spherical coordinates has also been developed.In chapter five, the theoretical basis and description to determine solution has been given, and the basic formulation of WSA has been deduced. Based on this, the holographic reconstruction and prediction formulations of the WSA based NAH have been built. The...