Active Control of Caudal Fin-Ray Stiffness and Propulsion

Fish fin ray features a unique bilaminar structure that comprises a pair of concave-shaped hemitriches, each of which is pulled independently by muscles to control the shape and stiffness of the fin ray. Fish precisely control the shape and stiffness of each ray to generate desired hydrodynamics forces on the fins. In the current study, the active control of the fin ray stiffness in propulsion through the hemitrich structure is studied using numerical simulations. A realistic fin-ray structure is constructed by including the two hemitriches and intra-ray layer. The fin ray control is implemented by specifying a dynamic hemitrich offset at the root. The effect of the dynamic parameters of the offset on the flexural stiffness and the resulted propulsion performance of the ray is investigated through flow-structure interaction simulations. The study is expected to improve the understanding of fish fin active stiffening in propulsion.