Gas Void Fraction Estimation in Gas-Bubble-Contained Sands with Difference Frequency Waves

Abstract

A nonlinearity parameter can be used for the estimation of the gas void fraction in gassy sediment. If two primary acoustic waves of different frequencies are incident on gassy sediment, nonlinear acoustic waves can be generated at the difference frequency. In the present study, the parametric acoustic array theory for the difference frequency wave was employed to estimate the nonlinearity parameters of gas-bubble-contained sands under laboratory conditions. The nonlinearity parameters of the sands were estimated between 10(3) and 10(4). Then, the estimated gas void fractions in the sands were between 10(-6) and 10(-4). They were similar to those estimated through the sound speed variation method. However, this linear acoustic method could not be applied to gas-bubble-contained sand with a low gas void fraction, because the sound speed variation was not observed in the sand. This study suggests that the nonlinear acoustic method seems very feasible to estimate the gas void fraction in gassy sediment with a low gas content. (C) 2012 The Japan Society of Applied Physics