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We consider theoretically the dynamics of an oscillated sessile drop of incompressible liquid and focus on the contact line hysteresis. We address the situation of the small-amplitude and high-frequency oscillations imposed normally to the substrate surface. We deal with the drop whose equilibrium surface is hemispherical and the equilibrium contact angle equals pi/2. We apply the dynamic boundary condition that involves an ambiguous dependence of the contact angle on the contact line velocity: The contact line starts to slide only when the deviation of the contact angle exceeds a certain critical value. As a result, the stick-slip dynamics can be observed. The frequency response of surface oscillations on the substrate and at the pole of the drop are analyzed. It is shown that novel features such as the emergence of antiresonant frequency bands and nontrivial competition of different resonances are caused by contact line hysteresis.
We consider the dynamics of monodisperse bubbly liquid confined by two plane solid walls and subject to small- amplitude high-frequency transverse oscillations. The period of these oscillations is assumed small in comparison with typical relaxation times for a single bubble but comparable with the period of volume eigenoscillations. The time- averaged description accounting for the two-way coupling between the liquid and the bubbles and for the diffusivity of bubbles is applied. We find nonuniform steady states with the liquid quiescent on average. At relatively low frequencies, accumulation of bubbles either at the walls or in planes parallel to the walls is detected. These one- dimensional states are shown to be unstable. At relatively high frequencies, this accumulation is found at the central plane and the solution is stable.