SUMMARY

Motivated by the incredible agility of fish and aquatic mammals underwater, scientists and engineers have sought to design biomimetic propulsion devices that can maneuver underwater with similar speed and efficiency. Robotic fish designs range from complicated models that replicate real fish to simple flexible flapping plates that represent abstractions of fish locomotion. Despite the apparent simplicity of the flexible oscillating plates, the thrust and swimming performance of an oscillating fin is dictated by the three dimensional interplay between inertia, elastic forces, and forces due to fluid-structure interaction. Thus, understanding the coupled hydrodynamics and solid mechanics of even a simple oscillating fin in a viscous fluid remains a challenge. In particular, if the plate is driven near the first natural frequency, the bending response is amplified due to resonance, which may increase swimming performance. In this work we use a fully coupled, three-dimensional FSI simulations to investigate the swimming performance of a simplified biomimetic propulsor. The computational model is a lattice Boltzmann method for the fluid mechanics, integrated with a lattice spring method to simulate the solid mechanics. The biomimetic swimmer is modeled as an oscillating elastic plate, and we hypothesize that resonance oscillations will contribute to increased swimming performance. We undertake a systematic study of multiple design parameters, such as mass, shape, non-uniform thickness, and actuation patterns, to understand the physics of the swimmer in free locomotion, or when it cruises forward with a balance between thrust and drag. Second, we explore strategies to control the direction of swimming by imposing asymmetric actuation patterns. While our results are primarily applicable for the design of simple biomimetic propulsors, they may shed light on some of the reasons many fish have tapered, low aspect ratio caudal fins.