Low-Frequency Underwater Acoustic Scattering Characteristics Of Targets In Shallow Sea Waveguides

The acoustic scattering characteristics of underwater targets are an important source of information on which active sonar depends.Different from the free field,the sound propagation in the shallow sea waveguides has multiple effects and multiple scattering between the target and the sea surface and bottom interface,which makes the target’s acoustic scattering characteristics more complicated.In this paper,based on relevant research at home and abroad,the simulation and evaluation of low-frequency sound scattering characteristics of complex targets in shallow sea waveguides are gradually carried out.This method uses a vertical cylindrical surface containing the target to divide the shallow sea waveguide into two areas.The area within the cylindrical surface uses normal wave theory to calculate the incident background sound field,and the multi-physics simulation software COMSOL Multiphysics to calculate the scattering sound field of the target.This solution deduces the general solution of the scattering sound field in the outer region of the cylindrical surface,and calculates the coefficient of the general solution based on the finite element calculation of the cylindrical surface sound pressure as the boundary condition,thereby calculating the scattering sound pressure at any observation point in the shallow sea waveguide.Next,the accuracy of the method is verified,and the various parameters or conditions involved in the application of the method are discussed,and the recommended parameter value principles are given item by item.Then the effect of multiple scattering of the target and the interface is demonstrated comparatively.When the distance between the target and the interface is close,that is,the target is close to the interface of the shallow sea waveguide,the effect of multiple scattering cannot be ignored,and the necessity of considering the multiple scattering of the interface is demonstrated.This method is a more accurate calculation method.Then the virtual cylinder calculation method is applied,in which the Benchmark model is used as a typical target.The simulation is carried out under different conditions such as the target at different depths,different distances,different incident azimuths,different receiving positions,etc.The relationship between the scattering characteristics of the target and various factors such as the environment is analyzed,and the mechanism analysis is carried out,and some laws of sound field scattering under different conditions are obtained.As a theoretical supplement and extension,this paper also introduces an external field experiment on the echo characteristics of the target in the waveguide.The virtual cylinder island method of the sound scattering of shallowwaveguide targets studied in this paper has the following advantages:(1): It can calculate the scattering of targets of any shape,not limited by the shape of complex targets,and can be applied to the simulation and evaluation of echo characteristics of complex targets in shallow waveguides;(2): The calculation method of the virtual cylindrical island is faster than the finite element method,and the calculation efficiency is higher;(3): This method takes into account the multiple scattering of the target and the interface.It can calculate the distance between the target and the interface,that is,the scattering of the target near the interface of the shallow sea waveguide.In addition,this method can be used not only for the calculation of backscattering echo characteristics,but also for the calculation of forward scattering characteristics in shallow sea waveguides.