Exploring the trade-off of lift and thrust during shrimp swimming

Shrimp use the dynamic morphology of their pleopods to maximize net thrust and produce the necessary lift to maintain their depth in the water column while cruising. Shrimp can achieve this by cupping the distal pleopod segment, composed of the endopodite and exopodite, which induces a change in the angle of incidence (AoI) of the exopodite. The exopodite AoI enables the distribution of forces into global lift and thrust. Using a biologically inspired robotic analog based on the Pleobot, we vary the cupping angle from 0° to 80° and the biologically relevant 35°. Through Particle Image Velocimetry, direct force measurements, and a reduced-order model, we investigate the mechanisms leading to the trade-off between lift and thrust-producing forces at different cupping angles. We found that changing the cupping angle modulates lift and thrust production, and drag-based thrust forces are primarily responsible for propulsion. Further, we show that propulsive forces produced by beating pleopods can be estimated using the linear superposition of drag and inertial forces based on measured morphological parameters. Our results elucidate the mechanism by which shrimp trade-off lift and thrust, which can be leveraged in developing and designing metachronal underwater vehicles.