Study On Reconstruction And Separation Of Non-stationary Sound Field For Planar Sound Source In A Uniformly Moving Medium

Near field acoustic holography(NAH)is an advanced acoustic technology with the functions of sound source identification,sound source localization and sound field visualization.In recent years,NAH technology has been diversified development.These technologies are carried out under the condition that the medium and sound source are relatively static.These technologies are no longer applicable when the medium is moving relative to the sound source.Therefore,the research on NAH technology in moving medium will be the future development trend.In order to expand the scope of NAH technology,this paper is based on the in-depth study of real-time NAH technology in uniform moving medium,in view of the limitation of two-dimensional spatial Fourier transform in the reconstruction of sound field by real-time NAH technology in uniform moving medium,such as winding error and Gibbs effect.This paper proposes an non-stationary sound field reconstruction method based on time-domain plane wave superposition.In this method,the double integral of two-dimensional spatial Fourier transform is directly discretized,which effectively avoids the limitation of two-dimensional Fourier transform for reducing the winding error and weakens the Gibbs effect.In the process of reconstructing non-stationary sound field based on time domain plane wave superposition method,the solution is unstable in the process of error accumulation and inversion due to too many iterations,a multi-step reconstruction method based on time-domain plane wave superposition method in uniform flow is proposed.This method reduces the total number of solutions,reduces the accumulation of errors and restrains the convergence of solutions instability.In order to expand the research scope of non-stationary sound field separation(NAH),a non-stationary sound field separation method based on two-sided sound pressure measurement in uniform moving medium is proposed for non-stationary plane sound source with non-free sound field in static medium.The specific research contents are as follows:In chapter one,the background and significance of research on NAH are described.Then the development process of stationary sound source research method from static medium to moving medium,the development process of non-stationary sound source research method from static medium to moving medium and the development process of sound field separation technology from static medium to moving medium are introduced in detail.The existing problems of the research methods are analyzed,and the content of this paper is determined.In chapter two,aiming at the problems of winding error and Gibbs effect caused by two-dimensional spatial Fourier transform in the process of non-stationary sound field reconstruction,a method of non-stationary sound field reconstruction based on time-domain plane wave superposition method is proposed.In order to compare with the later methods,this method is defined as a single-step method,which realizes the flat reconstruction under the condition that the moving direction of uniform medium is parallel or perpendicular to the holographic surface the non-stationary sound field reconstruction of area source.The effectiveness of the method is verified by numerical simulation,and the influence of signal-to-noise ratio,virtual source position,medium moving velocity and other parameters on the reconstruction results is further studied.In chapter three,aiming at the problem of error accumulation and instability in the process of perpendicular sound field reconstruction,a method based on multi-step time-domain plane wave superposition in uniform moving medium is proposed to realize the stationary reconstruction of non-stationary sound field.Numerical simulation shows the effect of sound field reconstruction,and further verifies the advantages of multi-step method compared with single step method in the case of virtual source surface,signal-to-noise ratio,calculation steps and so on,which proves multi-step method has a larger scope of application.In chapter four,for the plane sound source with non free sound field,an non-stationary sound field separation method based on double-sided sound pressure measurement under uniform moving medium is proposed to remove the influence of interference source and separate the non-stationary sound field radiated by the target source.The effectiveness of the separation technique is verified by the numerical simulation of three point sources.In chapter five,this paper summarizes the research content of this paper,and puts forward the problems to be solved in the future.