Caudal peduncle-inspired two-degree-of-freedom elastic coupling fin propulsion method

Abstract

Marine animals orchestrate the swimming process through the coordinated interplay of body musculature, the caudal peduncle, and the caudal fin. However, understanding the coordinated action of these components to achieve high propulsive performance remains a significant challenge. The study proposes a self-propulsive physical model with two-degree-of-freedom (DoF) elastic coupling inspired by the caudal peduncle, where the caudal peduncle exhibits spring-like behaviors influencing the tail's motion along heave/pitch directions. The complex nonlinear fluid–structure interaction issues are addressed via the nonlinear vortex sheet method. The study primarily compares the propulsive performance of the two-DoF elastic coupling caudal fin model with the pitch caudal fin model. Numerical results show that the peak efficiency of the proposed model is nearly eight times that of the pitch caudal fin model. Additionally, the study reveals that the high-propulsive mechanism lies in generating the figure of a butterfly phase diagram for the hydrodynamic forces and exploiting vortices to decrease energy consumption. These findings offer novel perspectives for the future design of high-efficiency underwater robots.