Kinematic modelling and hydrodynamic analysis of biomimetic pectoral fins of cownose ray

Recently, the exceptional manoeuvrability and stealth characteristics of manta-like fish have sparked significant interest in the development of bionic underwater vehicles. This study presents a novel kinematic model aimed at overcoming the difficulties associated with the current lack of understanding of the pectoral fin structure and the restricted range of motion of pectoral fins in conventional research approaches. This model intricately integrates a homogeneous coordinate transformation with the spanwise and chordwise motions of pectoral fins to precisely depict the substantial bending deformation characteristics of their movement. To examine the impact of these kinematic properties on the hydrodynamic efficiency, a thorough numerical analysis was conducted using computational fluid dynamics (CFD) on a 3D biomimetic pectoral fin under tethering conditions. The key findings indicated that the propulsion is mainly generated by pressure differences acting on the outer half of the pectoral fin surface. This analysis of pectoral fin hydrodynamics highlights that spanwise motion plays a crucial role in propulsion generation, whereas chordwise motion is essential for efficient propulsion of the pectoral fin. This study provides valuable guidance for the design of a biomimetic pectoral fin, thereby enhancing the applications of bionic cownose ray robots.