Elastic paddle design with three-dimensional reconfiguration for drag-based underwater locomotion

Manipulating the surface area of a paddle during the power stroke and recovery stroke is one of the locomotive strategies to enhance cyclic thrust in drag-based propulsion. Motivated by the unique shape and motion of the arms of a crinoid living in the ocean, the design of an elastic paddle consisting of multiple side flaps is proposed. The array of side flaps along the longitude of the paddle is allowed to undergo uni-directional deflection, resulting in a significant difference in the projection area of the paddle between the power and recovery strokes, which is beneficial to enhancing net thrust. To characterize the propulsive mechanism of the elastic paddle, its three-dimensional reconfiguration by fluid flow and drag generation is investigated using experimental measurements and theoretical analysis, and governing model parameters are derived.