Abstract
Low-frequency acoustic scatterings from a finite cylindrical shell are numerically analyzed by FEM. The simulation results show that the acoustic-scattering field in waveguide has lots of frequency-related sidelobes, while no sidelobes exist in free space at low frequencies. The simulation also indicates that the module value in waveguide can be almost 20 dB larger than that in free space at low frequency, which is caused by the ocean boundaries. We also demonstrate that when the incident wave direction is normal to the target at low frequency, the target strength will be maximum and the distribution of the acoustic-scattering field is axisymmetric about the incident waving direction. Meanwhile, the acoustic-scattering field is also related to the impedance of the seabed, and the change of the impedance makes just a little contribution to the scattering field. Finally, the influence of different target locations is analyzed, including the targets near the sea surface, seabed and the middle region of the ocean waveguide, respectively. From simulation results, it is evident that the distribution of the acoustic-scattering field at low frequency has a little difference, which is smaller than 0.5 dB with various target locations, and the change is frequency and boundary-related.
Highlights
Scattering has always been important issues in the history of underwater acoustic engineering
It is evident that the distribution of the acoustic-scattering field at low frequency has a little difference, which is smaller than 0.5 dB with various target locations, and the change is frequency and boundary-related
Considering the irregularity of realistic target shape, this paper uses the method of finite element to calculate the sound scattering field, just to discover some regular laws of the object scattering in the waveguide at low frequency
Summary
Scattering has always been important issues in the history of underwater acoustic engineering. Hackman studied the acoustic scattering field from an elastic spherical shell in a homogeneous, range-independent waveguide[3] Several methods, such as PE, theory of normal mode, theory of ray, FEM, BEM, and so on, have been developed for solving problems in both underwater propagation[4] and free-space scattering[5]. Considering the irregularity of realistic target shape, this paper uses the method of finite element to calculate the sound scattering field, just to discover some regular laws of the object scattering in the waveguide at low frequency. Since the shape of realistic objects may not be regular, this paper uses the method of finite element to calculate the scattering field of the target, combining the theory of the fluid-structure interaction with boundaries conditions. The medium is assumed to be a viscous fluid without damping
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