Mode locking for an externally excited droplet

When subject to external acoustic excitation, a droplet exhibits behaviour depending crucially on its initial shape and the period of excitation. For shapes close to the spherical droplet, approximate expressions can be derived for the Hamiltonian and the resulting motion is almost periodic. Of special significance is the sudden change in the form of the time-dependent Hamiltonian, when “mode locking” takes place. Due to “nonlinear resonance” the droplet exhibits behaviour completely unrelated to its perturbed state.