Transformation Technique Of Low Frequency Target Acoustic Scattering Characteristics Under Multistatic Detection Conditions

Multistatic target detection has the advantages of good concealment performance,wide detection range and strong anti-interference capability,and scattered echoes are the basis of the work.Most of the conventional multistatic scattering sound field calculation methods are based on each incident angle and receive angle to calculate one by one,how to predict the multistatic scattered sound field for a small amount of known scattering sound field information is of great significance in both underwater acoustic scattering experiments and underwater countermeasures.In this thesis,we carried out a study on multistatic scattering sound field prediction based on limited data,and establish a technique for transforming low-frequency target acoustic scattering characteristics for underwater multistatic detection conditions.The technique is based on the wave superposition method of scattering acoustic fields,and the far-field scattering acoustic pressure is represented as the form of the integral of the unknown source density function and the product of the acoustic scattering transfer function.The acoustic scattering transfer function is solved by numerical integration,using the target surface grid model as input.Using the acoustic scattering transfer function and a small amount of known scattering sound pressure data as input,the matrix transformation,acoustic reciprocity,and least-squares method are applied to determine the unknown source density function.Finally,the acoustic scattering transfer function and the sound source density function are multiplied to obtain the multistatic scattering sound field.In this thesis,the modeling process of the multistatic scattering sound field predicting method is formed with typical spherical and cylindrical targets,and the simulation calculation is verified for spherical and cylindrical targets.The multistatic scattering sound field of rigid sphere,double-layer spherical shell,spherical shell with stiffener,rigid cylinder,double-layer ribbed cylinder,tiled double-layer ribbed cylinder and underwater vehicle are solved by simple positive series solution and finite element method,respectively.The Gauss-Legendre integration method is used to find the acoustic scattering transfer function of each target,and several elements from the solved multistatic scattering sound field are taken as input data for each model to be predicted.The results are compared with the results of the full use of theoretical solutions/finite element calculations for the spherical and cylindrical targets,in which the density of the mesh profile,the number of input elements,the computational frequency,and the location of the input elements are used as variables.A multistatic target strength test was conducted on the lake using spherical shells with plywood and double-ribbed cylindrical shells as the target models to verify the prediction method of this topic by experimental means.The results of the experimental data processing and the finite element calculation of the target strength were compared,and the predictions of the scattering sound fields of the multistatic spherical shell with stiffener and the doublelayered ribbed cylindrical shell were made using the experimental data and the finite element data as input data respectively.The numerical simulations and experimental results show that this thesis is a feasible method for predicting the multistatic scattering sound field,with high computational accuracy,and has some practical value in scattering sound field experiment and calculation.