Efficient bio-inspired swimming with hybrid actuation

Conventional designs of bio-inspired robotic swimmers involve the oscillations of a caudal fin through an external actuation source to generate heaving motion. Recent advances in piezoelectric materials allow the fabrication of bio-inspired fins with an internal mode of actuation such as a distributed bending moment. Through three-dimensional computer simulations, we probe the effects a combined internal and external actuation of elastic fins on their hydrodynamic performance. The fin is modelled as a rectangular elastic plate, actuated at its root by a harmonic heaving motion and through its length by a distributed internal bending moment. We probe the effects of the phase lag between the external and internal actuation on the hydrodynamic thrust and efficiency. We show that the combined actuation can be tuned to work in synergy yielding thrust and efficiency that outperform each of actuation methods.