Flow Structures Produced by Robotic Sea Lion Flippers of Varying Elasticity and Angular Velocity

Sea Lions generate thrust through a clap-like maneuver, abducting their fore flippers towards the chest region of their body. This motion incorporates a combination of both lift and drag based propulsion and can produce high propulsive efficiency. Furthermore, it is unique amongst other biological swimmers that rely mostly on body-caudal fin locomotion. To replicate a simplified model of this maneuver for planar particle image velocimetry (PIV) in a water channel, we developed a robotic sea lion flipper model using silicon mold and a 3D printed skeletal structure representing the elbow, wrist, and knuckle joints. Using a motor, the elbow joint is rotated at a constant angular velocity into a flat plate, representing the sea lion’s chest, while the wrist and knuckle joints remain passive. To decouple the effects of flexibility and angular velocity on the resulting flow structures of the clap, we now present three robotic flippers models made with different flexibilities. The flow structures and estimated thrust are compared to a baseline rigid sea lion flipper model to allow for us to determine the isolated, decoupled effects.