Underwater Broadband Acoustic Scattering Modeling Based On FDTD

The scattering characteristics of underwater acoustic is an important topic in underwater acoustics at present, it can be used in the field of ocean exploration, ocean development, traffic navigation avoid etc. As underwater target is very complex, the calculation of complex target analytic method of underwater acoustic scattering has been difficult to complete. The finite difference time domain method(FDTD) is an important method for calculating the underwater acoustic scattering field. In this paper, the finite difference time domain method is used for broadband modeling and simulation of complex target under water acoustic field, there is a new gridding method and improved boundary condition. This paper provide effective modeling method for feature extraction of target under water.The main work of this thesis is as follows:(1) For broadband incident signal of different frequency, absorption coefficient of sound absorption in seawater is considered to improve FDTD iteration formula. The frequency dependent formula can be applied to the modeling and simulation of wideband incident signal under water.(2) Respectively use MUR absorbing boundary and the PML absorbing boundary condition for modeling and simulation. At the interface of seawater and the targets, sound transmission interface FDTD formula, which makes the sound waves can be transmitted into the target model, is used to make simulation more close to the actual situation.(3) Learn from the electromagnetic field, a complex target FDTD grid generation method based on triangular element is used to complex the grid of complex target, the realization of the complex target grid using 3ds Max software and visual studio.(4) The near to far field transformation uses Fourier transformation. When the incident wave is single frequency signal, the target is a sphere, far field sound pressure is derived from the near field by using the algorithm. The line array is used to receive sound in far field.(5) A plurality of targets are modeling and simulation. Compare different scattering field when incident wave is single frequency signal and broadband signal. Analyze specific points' waveform of computational domain. Verify the effectiveness of the improved FDTD method.