A Fast Calculation Method Of Bistatic Sound Scattering Of Underwater Targets Based On Acoustic Transfer Vector

Properties of underwater target scattering are important information sources for active sonar.In the past,much attention was paid to the monostatic backward acoustic scattering.However,with the development of low-frequency high-power multi-base active sonar,bistatic acoustic scattering characteristics of underwater targets have also become focus of research.In this paper,a method based on acoustic transfer vector is proposed to calculate the bistatic scattering sound field.This method believes that scattering sound pressure at the point of observation is equal to the superposition of scattered sound pressure contributed by each discrete unit on the target surface.Scattered sound pressure contribution by each unit,in turn,is equal to normal velocity of scattered sound field multiplied by an acoustic transfer vector whose physical meaning is far-field radiation sound pressure when the surface unit of rigid target vibrates at unit velocity.The result of simulation shows that the method is effective and feasible.In this paper,we first introduce the theoretical model of bistatic acoustic scattering calculation and deduce the calculation formula of bistatic sound scattering based on acoustic transfer vector.Compared with the traditional physical acoustics method,the formula fully integrates the target surface,i.e.,taking the contribution of dark areas into account.At the same time,new formula considers the influence of the curvature of the target surface,so it can be used to calculate the bistatic scattered sound field under the condition of big bistatic angle.Firstly,bistatic scattering acoustic pressure of rigid sphere and sphereand-cylinder assembly in free space are calculated.The validity and accuracy of new method are preliminary verified through comparison between the simulation calculation and analytical solution,the finite element solution.Secondly,new method is used to calculate the scattered sound field of the rigid sphere and the sphere-and-cylinder assembly in semi-free space.Calculation results are compared with analytical solution and finite element method solution to verify the applicability of this method.Then scattered sound field of rigid sphere in ideal waveguide is calculated and compared with analytical results calculated with image method.Results show that the two agree well.Finally,the method is used to calculate the bistatic scattered sound field of rigid sphere-and-cylinder assembly in ideal waveguide.Simulation results show that not only can the new method calculate monostatic sound field,but also have a higher computational accuracy in solving the bistatic problem.As singular integrals and inversions of highdimensional matrices are avoided,new method is obviously superior to boundary element method and finite element method in terms of calculation speed.To conclude,new method can be regarded as a compromise calculation method in terms of forecasting accuracy and forecasting speed and has certain engineering practical value.