On wave-driven propulsion

Wave-driven propulsion occurs when a floating body, driven into oscillations at the fluid interface, is propelled by the waves generated by its own motion. Wave-driven propulsion has been observed in the case of the waves generated by a honeybee trapped on the surface of water, in the case of “SurferBot”, a centimeter-scale interfacial robot that was inspired by the stricken honeybee, and at much larger scales, in the case of the waves generated by jumping up and down on a canoe, also known as “gunwale bobbing”.

In this talk I will present a new theory for wave-driven propulsion based on coupling the equations of motion of a floating raft to a quasi-potential flow model of the fluid. Using this model, expressions are derived for the drift speed and propulsive thrust of the raft which in turn are shown to be consistent with global momentum conservation. The validity of the model is explored by describing the motion of SurferBot, demonstrating close agreement with the experimentally determined drift speed and oscillatory dynamics. The efficiency of wave-driven propulsion is then computed as a function of driving oscillation frequency and the forcing location, revealing optimal values for both of these parameters which await confirmation in experiments.