Research On Selection Of Parameters And Reconstruction Error In The NAH Based On STSF

Near-field acoustic holography (NAH) developed in 1980s is a powerful tool for identifying noise sources and visualizing acoustic field. By measuring the complex 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. The theory of NAH based on the spatial transform of sound field (STSF) is presented first, developed most, and applied vast. The history of NAH has been reviewed, and the current status and problems to be solved have also been analyzed. The theory of NAH based on STSF is introduced. The selection of parameters and influence to error in the NAH based on STSF is studied. Which is enriched the theory of NAH. The thesis 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 different kinds of implementation algorithms, measure metholds, and measure systems of NAH have been analyzed. Then the solutions to these problems have been presented and the main research content of this thesis has been determined. In chapter two, the theory of the NAH based on STSF is introduced. The planar NAH and the cylindrical NAH theory is deduced. And the discrete of the formulas is presented in this chapter. The sphere NAH is simply introduced at last. In chapter three, by analysis of the NAH process, the noise distribution supposition in the k-space field is proved, and two estimated methods of the SNR are given. One is the energy estimated method, the other is the amplitude estimated. All the two methods are precise to the SNR estimate, and the energy estimated method is better.In chapter four, by discussion of the NAH forecast process and reconstruction process, and by analysis of the reconstruction error source, a new cut-off wave number selection methold is established. The different factors influence to reconstruction is comprehensively taken into account by this method, and the reconstruction error is greatly lessened compared with the now available experience formula.In chapter five, the reconstruction parameters selection is studied in detail for planar NAH. The relation of the sampling space, the sampling number and the dimension of the holographic plane is analyzed, and the suggestion on the selection of those reconstruction parameters is presented. The holography plane situation selection method is summarized. By the methods of this thesis, the reconstruction precision is efficiently improved compared with now other methods.In chapter six, the reconstruction parameters selection for cylindrical NAH is analyzed. There is a great difference between the planar NAH and the cylindrical NAH. The reconstruction parameters relation is researched and the parameters selection methods are suggested.In chapter seven, the research works in this thesis have been summarized, and the prospects to further study have been proposed.