Flapping dynamics of a multi-segmented structure bending uni-directionally

Considering flapping motion for drag-based swimming gait, the effective area of a propulsion unit is directly linked to the generation of thrust. In this study, the change in effective area is achieved through the deformation of an elastic structure used as the propulsion unit. Alike the articulated limbs of animals, an artificial multi-segmented structure with uni-directional elastic hinges connecting the segments is proposed. The uni-directionality of the hinges causes greater asymmetry of the deformation profiles between the power and recovery strokes and thereby enhances cyclic thrust. Experimental and theoretical analyses are conducted to investigate the deflection and drag characteristics of the structure undergoing flapping motions. To explore the effects of distributed flexibility and find the optimal configuration of the multi-segmented structure, kinematic parameters such as flapping amplitude and frequency and design parameters such as the number, location, and bending stiffness of the elastic hinges are varied. Through appropriate definitions of the bending stiffness and tip deflection of the whole structure, namely effective stiffness and weighted tip deflection respectively, the deflection of the multi-segmented structure could be well characterized.