Hysteresis and mode coupling in capillary bridge oscillations: Observations

We investigate nonlinear axisymmetric oscillations of capillary bridges in a Plateau tank of density-matched liquids. The liquids are selected to have unusually small kinematic viscosities. Large amplitude oscillations are excited by applying oscillating Maxwell stresses. The modal frequency response is measured by incrementing the excitation frequency. In a narrow range of frequencies the response depends on the direction (downward or upward) of the increments in a way consistent with a lumped-parameter model of hysteresis for weakly damped oscillators having a mode-softening nonlinearity. The bridge length is selected so that the third harmonic is the natural frequency of a higher-order capillary mode and that mode also exhibits hysteresis.