MAE Seminar: Performance of Ray Fins in Fish Locomotion – Effects of Stiffness Distribution

Abstract: Locomotion mechanisms of aquatic animals, with their characteristics of high efficiency, high maneuverability, and reduced environmental footage, have long been a source of inspiration for biomimetic underwater robotics. To date most of the studies have been focused upon imitation of fish swimming through body undulation and unsteady flapping of fins.

Fins of bony fishes usually consist of a soft collagenous membrane strengthened by embedded flexible rays. Morphologically, each ray is connected to a group of muscles so that the fish can control the rotational motion of each ray individually, enabling multi-degrees of freedom control over the fin motion and deformation.

We have developed 2-D and 3-D fluid-structure interaction models to simulate the kinematics and dynamics of structurally idealized fins. Our 3-D method includes a boundary-element model of the fluid motion and a fully-nonlinear Euler-Bernoulli beam model of the embedded rays. The 2-D model, on the other hand, stems from the immersed-boundary algorithm. Using these models we studied dynamics of both pectoral and caudal fins. It has been illustrated that the anisotropic deformability of the fin determined by distribution of the rays is essential to high propulsion performance. Specifically, it is found that for pectoral fins, a reinforced ray at the leading edge leads to performance enhancement, whereas the performance of a caudal fin is closely associated with the spanwise distribution of ray stiffness.