Differential and variational formalism for acoustically-levitating drops

We consider the most general problem of waves on the interface of two ideal fluids regarded as an ullage gas and a liquid, respectively. Separating the fast and slow time scales, we develop the differential and variational formalism for an acoustically levitating drop and determine its time-averaged shape (vibroequilibrium state of the drop). The vibroequilibrium states of the drop may differ from the spherical shape. Stable vibroequilibria are associated with the local minima of the quasipotential energy whose analytic form is also established