Effect of Whole-Body Flexibility of Caudal Fin on Propulsion Performance

Naturally evolved fish fins display superior qualities over conventional man-made thrusters by offering better maneuverability, less or no noise, and better efficiency. Caudal fin of a fish contributes most of the thrust force in fish swimming through body and fin undulations. Fish fins naturally happen to be flexible. The present work investigates the effect of whole-body flexibility of caudal fin on thrust production. A flexible trapezoidal fin is modeled as series of rigid segments connected with torsion springs and the governing equations of motion are obtained through multi-body dynamics approach. The hydrodynamic force acting on the fin segments is calculated as summation of drag and added mass force components. Simulations are carried out with different stiffness profiles for different motion parameters. The results show that flexible fins perform better than the rigid fin and different motion parameters require different stiffness profiles for higher thrust production and better efficiency.