Olivier Devauchelle (IPGP) - Bouncing droplets and gunwale bobbing

When a bath of silicon oil vibrates vertically, a droplet of the same oil can bounce indefinitely on its surface [1]. As it does so, it generates a Faraday wave around itself, which then pushes the droplet across the surface. Guided by its wave, the droplet interacts with its own trajectory, with the boundaries of the bath, or even with other bouncing droplets. This coupling has inspired a variety of models, from discrete dynamics tuned to the droplet's bouncing, to detailed numerical simulations of the flow in the bath. We propose a generic, continuous model which suggests that the behavior of the bouncing droplet do not hinge on the idiosyncrasies of the Faraday wave [2]. Based on this observation, we find it irresistible to draw an analogy with an unusual water sport often referred to as "gunwale bobbing" [3]. The point of this delicate art is to propel a watercraft, often a canoe, by making its hull oscillate vertically. We argue that the thrust thus induced results from the wave field that the canoe radiates.

[1] https://doi.org/10.1088/0953-8984/17/45/044

[2] https://doi.org/10.5802/crmeca.29

[3] https://arxiv.org/abs/2201.01533