Noise Source Identification Based On Acoustic Holography

Near-field acoustic holography is a powerful tool for identifying noise sources and visualizing sound field. Acoustic quantities such as sound pressure, particle velocity and sound intensity at any point in three-dimensional sound field can be reconstructed through the calculation of the measured sound pressure vector on the hologram surface. The applications of near-field acoustic holography especially in mechanical equipment sound source identification are restricted to some extent because some problems. The statistically optimized near-field acoustic holography has been researched deeply and developed. For sound source identification of irregular shape source, the combined near-field acoustic holography is presented. The simulation verification of the technology is done. The tests of double crank four ring-plate-type cycloid speed reducer are also completed. The main contents and conclusions are as follows:(1) The basic theory of FFT based near-field acoustic holography is introduced. The sound pressure and velocity reconstruction formula of statistically optimized near-field acoustic holography are systematically discussed in plane and cylindrical coordinates. The reconstruction process of statistically optimized double layer near-field acoustic holography is studied for the case of sound source at both sides of holography surface. The sound field separation technique through statistically optimized double layer near-field acoustic holography has been brought into the cylindrical coordinate.(2) The theory of near-field acoustic holography based on boundary element method is studied. The calculation method of acoustic transfer vector is introduced. In order to solve noise source identification of irregular shape source, the combined near-field acoustic holography is presented. This technology combines of two reconstruction algorithm, can identify the noise sources and sound field reconstruction by smaller test points.(3) The combined near-field acoustic holography belongs to acoustic inverse problem which has ill-posed nature. Small test errors can lead to the calculation value far away from the true value. The principles of regularization approaches and parameter selection techniques are researched. The reconstruction effects of different techniques are compared by numerical simulation analysis. The results provide the basis for the selection of combined near-field acoustic holography. (4) The acoustic transfer vectors of a double crank four ring-plate-type cycloid speed reducer are calculated. The vibration characteristics of the main component parts of the reducer are obtained after the tests of the reducer at different rotational speeds and different loads.(5) The noises are collected though holography array and the noise tests of the reducer are completed. The noise characteristics under different loads and rotations are achieved by combined near-field acoustic holography. The noise source is identified and the reducer surface velocity is reconstructed.