Hydrodynamics of biomimetic propulsion using externally and internally actuated fins

We combine experiments and computer simulations to examine the hydrodynamics of two different actuation types that can be used to actuate an elastic plate to serve as a biomimetic propulsor in robotic fish. In the first case the elastic palate is actuated to perform sinusoidal plunging at the root, whereas in the second case the actuation is due to a distributed internal bending moment that represents piezoelectric actuation of smart materials such as macro fiber composites. The Morison equation is often used to characterize the forces acting on oscillating submerged bodies in terms of two parameters: the inertia and drag coefficients. We evaluate these parameters using our simulations and experiments. We find close agreement between the experiments and simulations for both actuation types. We find that the inertia coefficient depends strongly on the actuation type and the magnitude of the trailing edge displacement. We rationalize this dependency by analyzing the differences in the kinematics of the plates with different actuation types. Our results are useful for developing efficient propulsors for biomimetic underwater locomotion.