Study of nonlinear oscillations and chaos of a bubble cluster in an oscillatory pressure field

1. 设计了一种新的激光捕获方法来控制气泡脱离接触的位置。这种方法是基于扫描薄激光束，其中光束的包络面是一个玉米。这种方法足以捕获上升的气泡，因为由于气泡界面处的折射引起的光动量变化所产生的势垒只存在于气泡的上部。通过这种方法可以捕获并成功地控制水中直径约10微米的气泡。结果表明，当激光功率为500mW时，作用在气泡上的侧向光力约为1pN，而在相同功率下，作用在气泡上的轴向光力约为6pN。讨论了质量扩散引起的被困气泡的稳定性。从理论上对力的强度和俘获态的稳定性进行了评价。结果表明，焦角越大，俘获力越强。考虑内部气体的热效应和气体的质量扩散，导出了球状或非球形气泡簇的控制方程。将该方程应用于多个相互作用气泡的非线性振荡。结果表明，当径向振荡的非线性变强时，内部气体的多向性关系不再成立。径向和表面振荡都受到每个气泡的平移运动的影响。由于气泡-气泡相互作用，相互作用的气泡比孤立的气泡更容易发生次谐波振荡。结果表明，由于内部气体的质量扩散，气泡振荡分岔并变为混沌的阈值减小。采用边界元法与有限体积法相结合的方法，研究了靠近平面刚性壁面的大变形气泡内部气体的热效应。结果表明，气泡内部的热传递加速了气泡的崩塌。气泡内部的温度分布强烈地依赖于气泡的变形程度。当射流在气泡壁上产生时，离刚性壁面最远的一侧的内部温度梯度变得非常陡峭。这种陡峭的梯度使液体温度提高到比单个气泡更高的水平。用边界元法研究了环形气泡的动力学。结果表明：液体微射流在形成气泡后，在液体内部形成高压区；高压区向刚性壁面移动，增加了壁面的压力。少

1. A new laser trapping method is devised to control the position of bubbles out of contact. This method is based on the scanning of a thin laser beam in which the envelope surface of the beam is a corn. This method is adequate to trap a rising bubble because the potential barrier made by the light momentum change due to the refraction at the bubble interface exists only at the upper side of the bubble. A bubble of about 10 mum in diameter in water is trapped and manipulated successfully by this method. It is shown that the optical force acting on the bubble in the lateral direction is about 1pN at 500mW of laser power, and in the axial direction about 6pN at the same power. The stability of trapped bubbles due to the mass diffusion is discussed. The strength of the force and the stability of the trapping state are also evaluated theoretically. The results show that the larger the focal angle is, the stronger the trapping force becomes.2. The governing equations of a cluster of spheric … More al or nonspherical bubbles are derived by taking account of the thermal effects of the internal gas and the mass diffusion of the gas. The equations are applied to the nonlinear oscillations of multiple interacting bubbles. It is shown that the polytropic relation for the internal gas does not hold when the nonlinearity of the radial oscillation becomes strong. Both radial and surface oscillations are affected by the translational motion of each bubble. The subharmonic oscillation of interacting bubbles occurs more easily than that of an isolated bubble due to the bubble-bubble interaction. It is also shown that the threshold value where the bubble oscillation bifurcates and becomes chaotic decreases due to the mass diffusion of the internal gas.3. The boundary element method (BEM) combined with the finite volume method is used in investigating the thermal effects of the internal gas on the dynamics of a gas bubble with large deformation near a plane rigid wall. It is shown that the bubble collapse is accelerated by the heat transfer inside the bubble. The temperature distribution inside the bubble is strongly dependent on the degree of deformation of the bubble. When the jet is produced on the bubble wall, the internal temperature gradient at the side farthest from the rigid wall becomes very steep. This steep gradient increases the liquid temperature to a level higher than that for the single bubble. The dynamics of toroidal bubbles is also investigated using BEM.The results show that the high pressure region is formed in a liquid after a liquid microjet threads a bubble. This high pressure region moves toward the rigid wall and increases the pressure of the wall. Less