Mimicking fish-like kinematics using fluid-structure interactions

We present here a new experiment on a clamped-free elastic slender plate under local harmonic forcing. In air, the solution consists in a sum of standing waves, whose frequencies, wavelengths and mode shapes are given by the Young modulus and the geometry. In more dense fluid, as water, and for specific parameters of the experiment, the solution switch from this standing waves solution to a pure propagating behavior leading to a fish-like kinematics. The existence of this regime allows to simply generate a propagating wave in a finite elastic medium avoiding a complex implementation of synchronized local perturbations all along the body. We show that the triggering of the propagating solution is due to the nonlinear nature of the fluid damping.