We present the results of a combined experimental and theoretical investigation of
millimetric droplets bouncing on a vertically vibrating fluid bath. We first characterize
the system experimentally, deducing the dependence of the droplet dynamics on
the system parameters, specifically the drop size, driving acceleration and driving
frequency. As the driving acceleration is increased, depending on drop size, we
observe the transition from coalescing to vibrating or bouncing states, then perioddoubling
events that may culminate in either walking drops or chaotic bouncing states.
The drop’s vertical dynamics depends critically on the ratio of the forcing frequency
to the drop’s natural oscillation frequency. For example, when the data describing
the coalescence–bouncing threshold and period-doubling thresholds are described in
terms of this ratio, they collapse onto a single curve. We observe and rationalize the
coexistence of two non-coalescing states, bouncing and vibrating, for identical system
parameters. In the former state, the contact time is prescribed by the drop dynamics;
in the latter, by the driving frequency. The bouncing states are described by theoretical
models of increasing complexity whose predictions are tested against experimental
data. We first model the drop–bath interaction in terms of a linear spring, then develop
a logarithmic spring model that better captures the drop dynamics over a wider range
of parameter space. While the linear spring model provides a faster, less accurate
option, the logarithmic spring model is found to be more accurate and consistent with
all existing data.