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An Investigation of the Flow Surrounding a Robotic Sea Lion Foreflipper Open Access

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Sea lions are part of one of the only groups of marine mammals that gener- ate propulsive forces through their pectoral appendages. Much research has been done regarding the hydrodynamics of body-caudal fin swimmers, however limited studies have been completed regarding sea lion locomotion techniques. Furthermore, sea lions and other pinnipeds live in both aquatic and terrestrial environments, so their body is adapted to these dual requirements. A greater understanding of sea lion foreflipper functionality could inform the designs of future autonomous underwater vehicles, as the dual-functionality allows for a large range of potential applications such as mine detection, shipwreck inspec- tion, underwater reconnaissance and terrestrial exploration.Through dye visualization and particle image velocimetry, the hydrodynamics of sea lion locomotion are studied using a robotic foreflipper. The robotic flipper is manufactured using a combination of 3D printing, silicone mixing pro- cesses and high-resolution scans of a California sea lion foreflipper. Actuation is controlled via a point-to-point scheme programmed through a servomotor. These studies indicate entrainment of water to the dorsal side of the flipper, producing vortex propagation directly off the tip that travels along the animal’s body. Velocity field analysis indicates a cutoff frequency after which efficiency of velocity production diminishes, leading to the conclusion of an ideal ratio between rotational velocity and tip speed.

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