Tuning the restitution coefficient of closed containers partially filled with water

It is well known that when open containers partially filled with water fall, a strong jet emerges after they hit the ground (Milgram, JFM, 1969). Surprisingly Antkowiak et al. (JFM, 2007) showed that if the water surface of the flow remains perfectly flat during the fall, no jet forms at all. In this work, we show how the shape of the water surface just before the impact not only has an effect on the presence of the jet but also on the rebound of the overall system (container$+$water). We focus in closed containers and study the influence of the filling fraction, which has been shown to be a relevant ingredient in the bouncing of spheres partially filled with grains and liquids on surfaces (Killian, Klaus, and Truscott, PoF, 2012; Pacheco-V\'{a}zquez and Dorbolo, Scientific Reports, 2013). Our analysis allow us to couple water-surface shape and filling fraction to estimate the momentum transfer and energy loss due to the internal motion of the liquid and link it with the restitution coefficient of the overall system. The understanding of this effect allow us to tune the coefficient restitution of the system before its release.