Effect of Stiffness on Batoid Undulation

Batoids (e.g., stingrays, skates, mobulas) have been a source of inspiration for engineering fast, maneuverable, and highly efficient propulsion systems. In emulating batoids’ most studies often employ a high number of actuators, leading to inefficient designs. This is because those studies ignore the influence of batoids’ fin morphology in combination with their skeletal system on swimming kinematics and efficiency. This study intends to induce batoid-like kinematics with simple excitation by emulating batoid internal and external morphology. The pectoral fin models are actuated vertically at different frequencies and amplitudes in different flow regimes Re=300 and Re=4000. By recording input force, amplitude and frequency and measuring thrust, output amplitude and chord wise flow we reveal the relationships between the structural properties and the hydrodynamics. By testing oscillator and undulator species and altering their internal stiffness by changing the number of artificial radials we map the effect of stiffness and shape on both structural response (output kinematics) and fluid flow. The results suggest that the different body styles show that oscillating batoid generate more thrust at higher stiffness, however undulating batoids create more thrust with lower stiffness. Additionally, we show the different vortex structures at different Strouhal numbers. The insights into pectoral fin shape and stiffness will help us design more efficient engineered propulsive surfaces.