Numerical and Experimental Study on Caudal Fin Oscillation Mode in Hemispherical Space

Attaining multidimensional movements, such as cruising, diving, and turning, is a crucial challenge in the development of bionic robotic fish. When only focusing on caudal fin movements, the caudal fin of a tuna generates significant lateral and propulsive forces and weak lift, while in contrast, the caudal fin of a dolphin generates significant lift and propulsive forces and weak lateral forces. The paper introduces a novel caudal fin oscillation mode for the hemispherical space, which extends the caudal fin oscillation features observed in tuna and dolphin to a broader range of organisms. Firstly, we presented the concept of hemispherical space caudal fin oscillation mode, and demonstrated the principle of lift distribution through theoretical calculations. Moreover, we detailed the force distribution obtained by the robotic fish under different caudal fin oscillation modes through numerical simulations. Finally, we experimentally validated the feasibility of the hemispherical space caudal fin oscillation mode. The results indicate that by modifying the oscillation mode of the caudal fin in bionic robotic fish, it is possible to distribute the lift generated by the fin movement to various forces that aid in achieving multidimensional movement, including propulsive, lateral, and lift forces.