Research On Reconstruction And Prediction Methods Of Sound Field In Limited Enclosed Spaces

In enclosed spaces such as aircraft,cars,ships,and submarines,the internal environment is complex,and the impedance between the internal air medium and the inner wall of the cabin is large,forming a serious reverberation sound field.In the civil field,the air noise inside the cabin can affect the comfort of passengers;In the military field,the air noise inside the cabin will also directly affect the combat performance of equipment.Therefore,by monitoring the air noise inside the cabin,the spatial distribution of the sound pressure is obtained,which not only has guiding significance for the improvement of the sound quality but also can monitor the faulty machine or equipment in time.At the same time,it can also provide support and guidance for the prediction of radiation noise outside the cabin.In this paper,we take a finite-length cylindrical shell with closed ends as a simplified research object and complete the research on the reconstruction and prediction method of the sound field in the closed space utilizing theoretical analysis,simulation calculation,and experimental verification of the cabin model.This paper mainly includes the following aspects:1.Aiming at the problem of poor low-frequency sound source recognition effect of a small aperture spherical array,this paper proposes a low-frequency sound source reconstruction method based on virtual spherical array expansion.Based on the principle of the acoustic’inverse problem’,this method can obtain a virtual spherical array with a larger aperture than the actual spherical array without changing the actual spherical array configuration,which improves the low-frequency spatial resolution of the original actual spherical array,thus broadening the application frequency band range of the spherical array.Through the simulation analysis of the parameters affecting the expansion accuracy of the virtual spherical array,the application scope and conditions of the virtual spherical array expansion method are given.The effectiveness and advantages of the method are verified by simulation analysis of typical examples based on a generalized inverse beamforming algorithm.In addition,the virtual spherical array and the actual spherical array are regarded as a virtual double-layer spherical array,and the array elements in the same direction(azimuth and elevation are the same)are used for finite difference processing to obtain the vibration velocity in the middle position of the array elements in the same direction.At the same time,the sound pressure at the position of the vibration velocity is obtained by using the virtual spherical array expansion method,and the open spherical array with vector array elements is obtained.The vector signal processing technology is introduced into the generalized inverse beamforming based on a spherical array.After deriving the transfer function of "sound pressure + vibration velocity",a generalized inverse beam formation algorithm based on the joint processing of "sound pressure + vibration velocity" is proposed to further improve the low-frequency spatial resolution of the spherical array.By carrying out the low-frequency sound source reconstruction experiment based on the open spherical array,the effectiveness of the virtual spherical array expansion method proposed in this paper is effectively verified in the low-frequency range.2.For the problem of sound field reconstruction in limited enclosed space,this paper proposes a local sound field reconstruction method based on spherical array monitoring and a full space sound field reconstruction method based on a cylindrical array.Firstly,the submarine cabin is simplified as a finite-length cylindrical shell model with closed ends,and the modeling method of the sound field in closed space under volume source excitation is given.Secondly,using a spherical array to obtain local sound field information in a closed space,a local sound field reconstruction method based on an equivalent source model was established based on the structure of the closed space and the internal source structure.The effectiveness of this method was verified through typical numerical examples.At the same time,the virtual sphere array expansion method is extended to a finite closed space,and a virtual open sphere array with vector elements is obtained by calculating the sound pressure gradient,which further improves the accuracy of sound field reconstruction in a closed space.Thirdly,considering the small aperture of the spherical array,it is impossible to obtain complete sound source radiation information simultaneously.Therefore,this paper uses the cylinder array to obtain the sound field information in the enclosed space,establishes a full-space acoustic field reconstruction method in the enclosed space based on the equivalent source model according to the enclosed space structure and the internal source structure,and verifies the effectiveness of the method through a typical example analysis.Finally,considering the complex environment of the finite enclosed space and the location of the source,a sound field reconstruction method in the enclosed space based on incomplete cylindrical monitoring is proposed,and a better sound field reconstruction effect in the enclosed space is obtained.3.Aiming at the problem of sound field prediction in enclosed space,this paper uses the sound field information of enclosed space monitored by a cylindrical array and proposes a sound field prediction method of finite enclosed space based on sound field prediction equivalent source model through the joint modeling method of enclosed space structure and volume source.This method transforms the sound field prediction problem into the sound field reconstruction problem through the joint modeling of the closed space structure and the internal volume source,which effectively avoids the singular integral problem caused by the internal source.At the same time,the sound field reconstruction problem in the closed space is transformed into the free field problem,and the sound field prediction in the limited closed space is realized.The effectiveness of the method is verified by simulation calculation of typical examples.In addition,considering a large number of monitoring points in the closed space,the compressed sensing technology is introduced into the calculation of the equivalent source model of the sound field prediction,and the number of monitoring points in the closed space is reduced while ensuring the accuracy of the sound field prediction.4.The experimental study of sound field reconstruction and prediction based on the cabin model is carried out.Aiming at the problem of sound field reconstruction and prediction in closed space,a sound field monitoring system in closed space based on an incomplete cylindrical array is developed.The sound source is wrapped inside the cylinder by scanning a double-layer incomplete cylinder(there is an equipment bracket at the bottom of the cabin model)along the circumferential direction of the cabin model through a double-line array.By arranging a microphone near the sound source as a reference point,the linear array scanning data is corrected to the data measured by all the elements of the cylindrical array at the same time.On the one hand,the outer cylindrical surface is used as the sound field monitoring point,and the inner cylindrical surface is used as the verification point of the sound field reconstruction.The experimental results verify the effectiveness and feasibility of the sound field reconstruction method proposed in this paper.On the other hand,the inner cylinder is used as the sound field monitoring point,and the outer cylinder is used as the verification point of sound field prediction.The experimental data processing results verify the effectiveness and feasibility of the sound field prediction method proposed in this paper.