Study On Double Planar Near Field Acoustic Holography Under One-dimensional Wave Propagation Equation

Near-field acoustic holography is an important way of noise source localization and recognition.Based on the measured sound field information near the noise source surface,the size and distribution of acoustic information on the noise source surface,and the acoustic field at any point outside of the source surface can be reconstructed,such as sound pressure,vibration velocity and far field directivity.Therefore,near-field acoustic holography is widely used in noise sources identification and structural strength analysis.At present,how to further improve the reconstruction accuracy of acoustic field has become one of hotspots in this direction.In this paper,the double-plane holographic measurement method combined with one-dimensional sound propagation equation and with extra measurement points outside of hologram planes is investigated for an underwater elastic structure by BEM.The singular integral problem is a key problem in acoustic holography by BEM.To deal with this problem,the one-dimensional sound propagation constraint condition and isoparametric transformation method are used separately for a submerged spherical shell model.Based on the previous work,a complex holographic acoustic field reconstruction method is proposed,in which the holograms are two parallel planes combined either with one-dimensional acoustic propagation points,or with transverse measurement points.The main factors related to the acoustic field reconstruction error by this method is numerically investigated,which includes measurement field point number,hologram's position,size and shape,and measurement point density,etc.In order to verify the validity of the proposed method above,an experiment was carried out in the free field and half-space acoustic field respectively by using a single-layer cylindrical shell as the experimental model.The experimental results show a well agreement with the numerical simulation results,and the acoustic reconstruction precision can be improved greatly.