Research On Noise Source Identification Method Based On Vector Array And Near-field Acoustic Holography

Near-field acoustic holography (NAH) proposed in 1980s is a powerful tool for identifying sound sources and visualizing sound field. By recording the sound pressures in the near-field, the acoustic quantities such as sound pressure, particle velocity, sound intensity and far-field directivity in the whole 3-D field can be reconstructed and predicted without the resolution limitation. In this paper, the development and the current status of NAH have been reviewed. After analyzing both the advantages and the unsolved problems of each kind of implementation algorithms of NAH, the solutions to these problems have been presented and the main research content of this dissertation has also been determined.During the reconstruction of the large size sources, for overcoming the rigid requirement on the measuring size of the hologram in the spatial transform of conventional NAH, the formulas of statistically optimal cylindrical near-field acoustic holography has been proved. Secondly, proposing the SONAH respectively based on the measurement of the pressure, the velocity and, the reconstructed results are compared. At last, for the sources existing on both two surface of the hologram, the acoustic field separation technique of SONAH has also been developed. Some simulations have been developed.At the same time, considering the limitation of the NAH in the reconstruction of the broadband acoustic field, the theory of the broadband cylindrical acoustic holography based on intensity measurement has been studied. Then, the discrete algorithm of complex sound pressure reconstruction on the hologram based on acoustic intensity measurement has been educed, and influence of measurement parameters on phase fluctuating error has also been discussed. At last, conducting the experiments based on the measurement of vector array, the effective reconstruction of source sound field has been achieved.In order to overcome the problem of non-conformable surface measurement, near-field acoustic holography based on boundary element method is studied. The ill-posed nature of the holographic process and its regularization strategy has been investigated deeply. The model of non-conformable surface of planar and cylinder has been discussed. The parameters choice of regularization approaches and several regularization parameter selection methods have also been introduced. The results showed the merits of "Tikh+GCV" in regularization strategy.Aiming at the problems in the reconstruction process and basing on the SONAH, BAHIM and BEM, this paper proposed two multiple NAH methods, that is, hybrid NAH based on intensity measurement and BEM and hybrid NAH based on SONAH and BEM. The two hybrid methods integrate with other methods, which apply to non-conformable model and overcome the shortcoming of measurement surface and reconstructed distance and ill-posed nature. This two hybrid NAH methods expand the scope of the applications of NAH.After a vector sensors array device and the measurement method of underwater near-field acoustic holography had been designed, the experiments on underwater near-field acoustic holography measuring by the vector sensors array are carried out in conformable experimental model and non-conformable experimental model. The results demonstrated that near-field acoustic holography and underwater near-field measurement method based on the vector array is applicable and powerful.At last, the research results obtained in this dissertation have been summarized, and the topics need further study have been pointed out.