Realization And Application Of Diffusion Sound Field In Non-anechoic Tank

Underwater acoustic measurement is very important for the development of underwater acoustics.As an important equipment in acoustic measurement,non anechoic water tank has the advantages of low construction cost and wide application range.The assumption of diffusion sound field originates from the indoor acoustics,which means the sound field in the closed space with uniform average sound energy density distribution.,it can only be approximately satisfied when the cutoff frequency is above in the reverberation room with good reflection performance.Due to the poor diffusion of the sound field in the conventional non anechoic water tank,the measurement error of the fixed field points is very large,and the method of spatial average is used to get the measurement results accurately,but a large number of measurement points are needed.According to the reciprocity of sound field,this paper has studies the method of improving the diffusion of sound field by means of multiple sound sources and undulating interface.The spatial average in the reverberation tank with higher diffusion degree can improve the measurement accuracy,simplify the measurement steps and improve the measurement efficiency.This paper studies the sound field of non anechoic water tank from three aspects: theoretical analysis,simulation and experiment.Firstly,according to the theory of closed space,the characteristics of sound field in non anechoic water tank are analyzed from two aspects of statistical acoustics and wave acoustics.It is determined that the spatial fluctuation of sound field in non anechoic tank is due to the interference between normal waves.Then,by using the finite element software,the diffusion of sound field under the excitation of single frequency and white noise is analyzed,and the relationship between the number of measurement points and the bandwidth and the diffusion degree of sound field is analyzed.At last,the acoustic characteristics and field diffusivity of the tank are measured in the non anechoic tank.The results show that in the non anechoic water tank,only when the mode density is large enough and the cutoff frequency is high enough,the condition of dispersion field can be satisfied;the diffusion of sound field is related to the analysis bandwidth,single frequency is not conducive to the formation of diffusion field,white noise excitation is conducive to the diffusion of sound field;random boundary can improve the diffusion of sound field,and multi-source can improve the broadband noise excitation of multi-source sound The diffusion of the field plays an important role on the premise that the broadband noise excitation and the distance between sound sources are larger than the wavelength.The combination of the two methods can effectively reduce the uncertainty of measurement.This paper presents a method to improve the diffusion of sound field by using multiple sources and undulating interfaces,which is of great significance for underwater acoustic measurement based on closed space.