Experimental Study of a Flexible Oscillating-Foil Propulsion System With Variable Stiffness and Inertia Available to Purchase

Considerable effort has been devoted to the development of flexible flapping fins and wings as propulsion mechanisms for robotics applications. The present work contributes to this research field by considering the effects of inertia, stiffness, resonant frequency and oscillation kinematics on the thrust generation and efficiency of flexible oscillating foils. The findings are derived from experimental measurements of the forces applied to foil models, which were undergoing an oscillating motion in water. In addition, a semi-empirical model of the foil structure was developed to characterize the fluid-structure interaction phenomena. The ratio of the oscillation frequency to structural resonant frequency was found to be one of the principal parameters, which determined the propulsive efficiency. However, when comparing the performance of foils with equivalent resonant frequencies but different levels of stiffness and inertia, stiffer and heavier foils were found to achieve greater thrust production. The improved performance of the heavier foils compared to lighter ones is attributed to a decrease in the damping ratio. The lower damping ratio allowed for a greater amplitude of the motion of the deforming part of the foil which resulted in increased thrust.