Research On The Free Field Recovery Technique Based On BEM

It is necessary to obtain the measurement data of sound pressure and vibration velocity under the condition of free space when the pressure field of target source is reconstructed.But in the real environment,the disturbing factors are inevitable,such as the disturbing source in the surrounding environment and the scattered field of structure itself.In order to remove the influences of disturbing factors in bounded noisy environment and obtain the free field of the target source,the free field recovery technology based on boundary element method is investigated.The free field recovery technology requires the information of double layer pressure field on two parallel closed holographic surface surrounding target source.Firstly,particle velocities of holographic surface are calculated by the Euler's equation combined with finite difference.Secondly,the ingoing and outgoing pressure fields are separated while applying internal and external acoustical methods.Then the rigid scattered field can be calculated under the rigid body assumption using BEM.In the end,it is recovered accurately that the free field of target source in the holographic surface.In this paper,the basic BEM program is implemented in which some problems are solved,including singular integral and not-unique solutions.On this basis,field separation algorithm and free field recovery algorithm considering the influence of rigid scattered are implemented,and the effectiveness is verified by numerical examples.Due to the difference between rigid and elastic components of scattered field in different acoustical media,the recovered effect varies a lot in practical engineering application.In this paper,it is analyzed that the scattered fields of typical structures in different acoustical media,and the application suggestions for free field recovery technology are given.Then the recovered free fields of square box in air and cylindrical shell underwater are realized successfully,which provides certain references for the practical application of free field recovery technology.