An Investigation On Nonlinear Behavior Of Cavitation Bubbles Under The Excitation Of Acoustic Waves

Acoustic cavitation is critical in biomedical,chemical and other engineering applications due to its tremendous chemical and mechanical effects.The effects of cavitation could be enhanced when the bubble is under the excitation of multi-frequency acoustic wave,which could be shown as follows,sonoluminescence will be improved,efficiency of sonochemical reactor increased,and accuracy of ultrasound imaging higher But the cavitation bubble is easily to show some nonlinear characteristics,such as chaotic oscillation,under the excitation of acoustic wave.This would affect the application of acoustic cavitation in the fields aforementioned.Hence,it is necessary to thoroughly reveal dynamic characteristics of the bubble under the excitation of acoustic wave and the effect bubble size distribution had on the acoustic wave.In this thesis,it is studied that the nonlinear characteristics of cavitation bubble under dual-frequency acoustic excitation and the effect of bubble size distribution had on acoustic wave when it is traveling through dilute polydisperse bubbly liquids.The study of the effect on the nonlinear behavior of the bubble is focused on amplitude,energy allocation and initial phase difference of the dual-frequency acoustic wave.The Keller-Miksis equation is adopted to fit the interface motion equation of the bubble.Then it is solved in MATLAB using the forth-order Runge-Kutta method.Time domained diagram,phase diagram,bifurcation diagram and Lyapunov exponent spectrum are employed to analyze the results.Acoustic bubble will oscillate periodically when the amplitude of acoustic is low,with little influence of the initial phase difference.As the amplitude increases,the initial phase difference works more and more evidently,with the appearance of period-doubling cascade and chaotic oscillation.As to the counter effect of bubble size distribution had on the acoustic wave,phase velocity and attenuation of the acoustic wave are discussed in this paper,with the bubble size distribution fitted based on Gaussian distribution function.The phase velocity and attenuation varies with the standard deviation change visibly.Among these variations,the minimum phase velocity and maximum attenuation change the most.