Research And Application On Noise Source Identification Based On Beamforming

Noise source identification technique plays an important role in controlling product noise radically,beamforming is a noise source identification technique that is well suited to engineering applications.However,there are still some defects in beamforming which limit its application in engineering.Firstly,the conventional beamforming technique needs to be carried out in a free field.Secondly,in the process of identifying moving sound sources,the conventional beamforming technique cannot locate the sound source accurately because of the Doppler Effect and the influence of the near-field term in the moving sound source radiation.To overcome the two problems existed in conventional beamforming techniques,the specific contents are as follows:Two commonly used and most representative beamforming algorithms,delay and sum algorithm and multiple signal classification(MUSIC)algorithm,are introduced in this thesis.The influence of frequency,measuring point spacing,measuring distance,signal to noise ratio on the two algorithms are analyzed and the computational efficiency of the two algorithms are compared through numerical simulations.Finally,the two algorithms are verified by experiments.A sound field separation method suitable for beamforming technique is proposed to suppress the influence of disturbing sources,which is called sound field separation method based on sound pressure gradient.Compared with the existing method(the sound field separation method based on plane wave),the proposed method improves the sound field separation accuracy when the distance between two measurement surfaces is large or when the frequency is high.The proposed method and the sound field separation method based on plane wave are compared by numerical simulation.The results show that the method proposed in this thesis is applicable to a wider frequency range and insensitive to the distance between two measuring surfaces.Therefore,there are few restrictions in application.Finally,the effectiveness of the proposed method is verified by experiments.Based on the analysis of the principle of Doppler Effect of a moving sound source,a method to eliminate Doppler Effect by using time interpolation is proposed.The pressure after eliminating Doppler Effect is then substituted into the conventional beamforming technique,and the moving sound source is identified effectively.However,when the sound source moves at a high speed or the sound source frequency is low,the above-mentioned identification technique will produce a large identification error.To solve this problem,a moving source recognition method that considers the near-field term is proposed in this thesis,which can not only break through the sound source moving speed and sound source frequency,and can get the time-domain source signal.Finally,the effectiveness of the proposed method is verified through numerical simulation.