Collective hydrodynamics of robotic fish

Many animals in nature travel in groups either for protection, survival, or endurance. Among these, fish do so under the burden of hydrodynamic loads, which incites questions as to the significance of the multi-body fluid-mediated interactions that facilitate collective swimming. We study such interactions in the idealized setting of a rotational array of robotic fish whose tails undergo a prescribed flapping motion, but whose swimming speed is determined as a natural result of the hydrodynamic effects. Specifically, we examine how the collective speed of the swimmers varies with the frequency and amplitude of their tail flapping, and with the phase difference between the tail motions of neighboring robots in the array. To visualize the flow field while the swimmers are in motion, we implement a camera system to track neutrally buoyant florescent seeding particles suspended in the water surrounding the fish. This three-dimensional particle tracking velocimetry technique allows us to capture the trajectory of the seeding particles and, thereby, derive the velocity and vorticity fields around the interacting fish. Applications that can directly benefit from the findings of our investigation include the design and control of robotic fish swarms.