Bayesian Near-field Acoustic Holography Approach And Application

Near-field acoustical holography(NAH)is an effective technique of source inversion and visualization.It can reconstruct and predict the acoustic information in three-dimensional sound field by measuring the sound field on the surface of radiation source,such as surface vibration velocity and sound pressure.It has become a powerful tool to study and solve the problem of mechanical noise.However,in order to meet the needs of the application of near-field acoustic holography in engineering practice,some theoretical and technical limitations,such as the ill conditioned problem of sound field reconstruction,need to be studied and solved.In this background,this dissertation studies and develops the Bayesian near-field acoustic holography approach,demonstrates the technology through simulation and experiment,and carries out the experiment with application to the gearbox,which paves the way for the application of near-field acoustic holography technology towards engineering practice.The research work of this dissertation is summarized as follows:(1)Bayesian NAH is introduced.Based on the propagation model of sound field,the relation between sound source surface and holographic measurement surface is established,and the ill conditioned problem of sound source reconstruction and the need for regularization are pointed out.Based on Bayesian principle,the full Bayesian approach for optimizing parameters are developed.Bayesian parameter estimation is applied to the reconstruction of source surface normal velocity.By combining the aperture function and the selected regularization parameter by marginal likelihood maximization,an accurate reconstruction of the sound source is achieved.(2)Numerical simulation of source inversion is extensively carried out.Through the numerical simulation of the source location,the effectiveness of the proposed approach is demonstrated.Then,based on the simulated sound pressure data,Bayesian NAH is used to reconstruct the surface velocity distribution of a simply supported plate.The results show that the reconstructed value of the vibration velocity is in good agreement with the theoretical one,which proves the validity of the approach.(3)The sound source inversion experiment and application research are carried out.First,a microphone array support is designed and manufactured in order to carry out acoustic experiments.The inversion experiments of single and double sound sources are carried out,and followed by the reconstruction experiments on the vibration velocity of a metal plate.The inversion accuracy of the proposed approach is discussed.Finally,the experiment application of reconstructing the surface vibration velocity of gearbox is carried out,and the noise characteristics of gearbox are revealed.This dissertation provides an alternative approach for the non-contact vibration test and noise analysis of mechanical structures,which has certain guiding significance for the vibration and noise control and optimization design of mechanical structures.