To determine the two-dimensional kinematics of the California sea lion foreflipper during thrust generation, a digital, high-definition video is obtained using a non-research female sea lion at the Smithsonian National Zoological Park in Washington, DC. The observational videos are used to extract maneuvers of interest--forward acceleration from rest using the foreflippers and banked turns. Single camera videos are analyzed to digitize the flipper during the motions using 10 points spanning root to tip in each frame. Digitized shapes were then fitted with an empirical function that quantitatively allows for both comparison between different claps, and for extracting kinematic data. The resulting function shows a high degree of curvature (with a camber of up to 32%). Analysis of sea lion acceleration from rest shows thrust production in the range of 150-680 N and maximum flipper angular velocity (for rotation about the shoulder joint) as high as 20 rad s⁻¹. Analysis of turning maneuvers indicate extreme agility and precision of movement driven by the foreflipper surfaces.
Abstract-Underwater propulsion that leaves little traceable wake structure while producing high levels of thrust is a highly desired goal. A potential biological model is the California sea lion, a highly maneuverable aquatic mammal that produces thrust primarily with its foreflippers without a characteristic flapping frequency. In an effort to mimic the sea lion flipper, a flipper from a sea lion carcass has been scanned using several non invasive methods with the goal of manufacturing a robotic flipper with identical geometry. The scanning methods are hereby compared for overall quality, accuracy, and level of detail captured.
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