The Low-Frequency Acoustic Scattering Characteristics Study on Underwater Elastic Targets by the Coupled FEM-BEM Method

Abstract

Abstract A mathematical model about calculating acoustic scattering of elastic shell with air inside unbounded fluid was developed using a coupled finite element and boundary element technique. The coupling of elastic shell with air and shell with fluid was included in this model. To validate the scheme, the scattering characteristic of spherical shell with air submerged in water was calculated. Comparison of the numerical results with the corresponding analytical solutions shows that they are in good agreement in low frequency. On this basis, the low-frequency acoustic scattering characteristic of underwater elastic target was calculated with this method. The results showed the shell thickness and material have little effect on the target strength in the transverse direction, when the frequency is 100-300 Hz. In the omni-direction, the target strength of titanium alloy shell is higher than that of steel shell, and the larger the shell thickness, the greater the target strength. As the frequency is 200 Hz, the steel shell with a thickness of 28 mm has the phenomenon of acoustic resonance, resulting in a sharp increase in the target strength.