  When a container is set in motion, the free surface of the liquid starts to
oscillate or slosh. Such effects can be observed when a glass of water is
handled carelessly and the fluid sloshes or even spills over the rims of the
container. However, beer does not slosh as readily as water, which suggests
that foam could be used to damp sloshing. In this work, we study experimentally
the effect on sloshing of a liquid foam placed on top of a liquid bath. We
generate a monodisperse two-dimensional liquid foam in a rectangular container
and track the motion of the foam. The influence of the foam on the sloshing
dynamics is experimentally characterized: only a few layers of bubbles are
sufficient to significantly damp the oscillations. We rationalize our
experimental findings with a model that describes the foam contribution to the
damping coefficient through viscous dissipation on the walls of the container.
Then we extend our study to confined three-dimensional liquid foam and observe
that the behavior of 2D and confined 3D systems are very similar. Thus we
conclude that only the bubbles close to the walls have a significant impact on
the dissipation of energy. The possibility to damp liquid sloshing using foam
is promising in numerous industrial applications such as the transport of
liquefied gas in tankers or for propellants in rocket engines.
