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2019_programme: SOUND SPEED AND ATTENUATION PREDICTIONS USING THE CORRECTED BIOT MODEL FOR GAS-BEARING MARINE SEDIMENTS

** Session: **17. Modeling techniques for underwater acoustic scattering and propagation

** Organiser(s)****: **Gunderson Aaron, Isakson Marcia
** Lecture****: **SOUND SPEED AND ATTENUATION PREDICTIONS USING THE CORRECTED BIOT MODEL FOR GAS-BEARING MARINE SEDIMENTS

** Paper ID: **799

** Author(s)****: **Zheng Guangying, Xu Chuanxiu, Shao You

** Presenter: **Zheng Guangying

** Presentation type: **oral

** Abstract: **As is well known, a small volume of gas bubbles existing in a sediment can greatly change the sound speed and attenuation in marine sediment. In this work, to investigate the sound propagation in a gas-bearing marine sediment, we integrate the volume vibrations of bubbles in pore water into the continuity equation of pore-fluid filtration in porous medium based on Biot theory, so as to obtain the continuity equation of pore-fluid filtration with bubble pulsation. On this basis, according to the relationship between the instantaneous radius of bubble and the background pressure of the medium under the linear vibration of bubble, as well as the equations of motion of the fluid medium and porous medium, a new displacement vector wave equation of porous medium under the influence of bubble is derived, which establishes the model for the sound speed dispersion and attenuation prediction under the gas-bearing sediments. The acoustic properties of gas-bearing sediments show three distinct zones of frequency-dependent behavior in numerical analysis. For the insonifying frequency below the gas-bubble resonance frequency, the phase velocity is lower, and the attenuation coefficient is significantly higher than that in non-gassy sediments. A transition zone near the resonance can be observed, in which the phase velocity rapidly increases. In particular, the phase velocity can highly exceed the non-gassy velocity at the resonance frequency. The attenuation is highest at frequencies close to the gas-bubble resonance frequency, which depends mainly on the bubble radius. Above the resonance, the phase velocity approaches a constant value similar to the non-gassy sediment, whereas the attenuation is higher than non-gassy attenuation and increases with the increasing frequency.

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** Corresponding author: **Dr Zheng Guangying

** Affiliation: **Hangzhou Applied Acoustic Institute

** Country: **China

** e-mail: **