Inst. of Acoust., Nanjing Univ., Nanjing, People's Republic of China
Dept. of Phys., Univ. of Vermont, Burlington, VT 05405
It has been known for some years that the presence of bubbles enhance the nonlinearity of a liquid dramatically. Wu and Zhu [J. Acoust. Soc. Am. 89, 2634--2639 (1991)] measured the nonlinearity parameter B/A of water containing a three-dimensional ensemble of randomly distributed uniform-sized trapped cylindrical bubbles. The measured effective B/A for the system is of the order of 10[sup 4] to 10[sup 5], when the bubbles were driven at their resonance frequency. A physical model of a second-order nonlinear wave equation taking account of dissipation as well as the variation of air volume fraction due to bubbles' pulsation at resonance is developed. The results calculated using this model are in good agreement with the experimental values.