Analysis of Shrimp Appendage Cupping on Swimming Performance through a Bio-inspired Model

Shrimp can adapt to their environment through dynamic morphology, contributing to their remarkable maneuverability and efficiency during swimming. Integral to this morphological adaptability of shrimp is the cupping of leg appendages (pleopods) during their power and recovery stroke. Cupping occurs through the change in the cupping angle between each endopodite and exopodite pair that make up a pleopod. This cupping angle contributes to the actuation of the exopodite to spread outward (abduction) during the power stroke and to move inward (adduction) during the recovery stroke. Previous studies have given insight into these pleopod kinematics. However, the optimal angle of pleopod cupping for different swimming modes and hydrodynamic conditions still needs to be explored. Here, we use biological studies of shrimp to guide the design of a robotic pleopod, which we leveraged to investigate the hydrodynamics of pleopod cupping. Through Particle Image Velocimetry (PIV) experiments and force measurements, we examine the thrust, lift, and vortex generation across a range of cupping angle configurations. We compare the cupping angle of optimal efficiency to the cupping angle found in shrimp (approximately 35°) to understand the trade-off between lift and thrust generation. Implementing the optimal cupping angle will ensure the maneuverability of future underwater metachronal robots under different environmental conditions.