Research On Low-Frequency Scattering Characteristics Of Underwater Targets

Scattering characteristics of underwater targets are the important applied foundation researches of underwater acoustic technique. With the great application of the acoustic tile in modern submarine, it's more and more difficulty to detect the complicated underwater targets long distance. For the sake of avoiding the absorbability of the acoustic tile and extending the detection range, the new active sonar turns to be large power and low-frequency. Therefore, the researches on low-frequency scattering characteristics of underwater targets become more and more important.By far, the engineering applicable methods of calculation of the target scattering characteristics are basically based on the physical acoustics method, Kirchhoff approximation, i.e. high frequency plane wave approximation. It is a high frequency applicable method. When researching the low-frequency scattering characteristics of underwater targets, the target scattering may enter the resonance region or the Rayleigh region in the low frequency area and lead to error. Corresponding to this kind of conditions, this paper based Finite Element Method (FEM) and Boundary Element Method (BEM), using SYSNOISE, a commercial acoustic analyze software, calculating and validating the scattering characteristics of underwater targets.Firstly, the scattering characteristics of elastic sphere shell, rigid sphere, hemi cylinder are calculated. By contrasting calculation results from the academic data, the conclusion is that it's feasible to use SYSNOISE to calculate the low-frequency scattering characteristics of simple model which is elastic and rigid.The accurate geometric model of the simple benchmark submarine are built. Using the software of SYSNOISE, the scattering characteristics of the model are calculated at the frequency of 200Hz, 400Hz and 1000Hz. The results are compared with that in the foreign literature using the BASIS prediction model and planar element method. It shows that in most angle, especially in 90°(±20°),the results from SYSNOISE are in good agreement with BASIS. But at the head and end aspect, the results from SYSNOISE have a difference about 10dB with the BASIS. Finally, using the planar element method, the target strength of Benchmark submarine are calculated. By compared the results at the condition with the acoustic tile and non, the effect of acoustic tile is not obviously at low frequency, the effect of acoustic tile become visibly with the increase of frequency.The study on low-frequency scattering characteristics of underwater targets has offered a new way to obtain the target strength of a submarine in low frequency by use SYSNOISE, which has some virtues such as high speed and precision correspondingly, result viewable etc. It can be obtained that SYSNOISE and the methods in common use are equivalent in predicting the scattering characteristics of underwater targets.