| Submarine as the most threatening underwater hidden combat platform.Stealth performance has always been one of the most important performances of submarines.As the submarine’s noise level continues to decrease,the acoustic target strength has become the most important indicator for measuring the submarine’s stealth performance.At present,the methods for studying the acoustic target intensity of underwater structures can be divided into two types: frequency domain method and time domain method.In this paper,based on the finite element method and the plate element method,the simulation and analysis of the underwater target’s radio frequency domain characteristics are carried out,and then the time domain characteristics are simulated and analyzed based on the finite element method.Finally,based on these calculation methods,several typical engineering problems of acoustic scattering are calculated and analyzed.The specific work is as follows:The acoustic target intensities of underwater elastic spherical shells and infinitely long cylinders were modeled and calculated using two-dimensional axisymmetric and two-dimensional spatial dimensions commercial finite element software COMSOL,respectively.Then the finite element results are compared with the theoretical results to verify the effectiveness of the finite element method and these two simplified processing methods.Then the plate element method was used to calculate the acoustic target strength of the rigid ball and Benchmark submarine,which were compared with the theoretical solution and the BASIS method,respectively,and the effectiveness of the plate element method to calculate the target strength of the rigid object was verified.Then,for rigid enclosures,water-filled steel enclosures and vacuum steel enclosures,the target strengths under normal and transverse incidence were calculated using the finite element method and the plate element method,respectively.The applicability of the plate element method in calculating the target strength of elastic objects was evaluated.The time domain waveform of the echo of the aluminum spherical shell in the case of truncated sine wave was calculated using the pressure acoustic transient module of COMSOL software.The results are compared with those in the literature to verify the accuracy of the time-domain finite element method.For the near-field echo strength of the aluminum sphere,the Gaussian plane wave and the point sound source are used as incident waves to calculate the time-domain echo of the aluminum sphere.The frequency-domain sound pressure is obtained after FFT of the incident wave and echo.The frequency-domain sound pressure of the incident wave and echo is brought into the formula to compare the echo strength calculated with the frequency-domain finite element calculated echo strength,and the relevant conclusions are obtained.For the far-field acoustic target strength of the aluminum sphere,the plane Gaussian wave is used as the incident wave,and the far-field frequency-domain scattered sound pressure is directly obtained by using the software’s own research.The far-field frequency-domain scattered sound pressure and the existing incident-wave frequency-domain sound pressure were brought together into the formula and calculated to obtain the far-field acoustic target strength,which is compared with the theoretical solution to obtain a comparison conclusion.The COMSOL software was used to calculate the curve of the acoustic target strength with the axial plate position when the angle of incidence of the infinite cylindrical shell with axial plate changes underwater.After analysis,a certain pattern is obtained.The formula of the plate element method is studied,and the relationship between the acoustic target strength of the submarine substructure and the acoustic target strength of the whole submarine is summarized,which provides a method choice for studying the influence of a certain submarine substructure on the acoustic target strength of the whole boat.The time-domain finite element method was used to calculate the sound waves recorded at the measuring point under the condition of free liquid surface and obstacles under water,which provided a reference for the selection of hydrophone position,target position and sound source position in the experiment. |
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