Underwater collision avoidance using undulating elongated fin propulsion

Underwater navigation to survey littoral regions or complex environments such as offshore structures, coral reefs or sensitive coastal zones requires a highly maneuverable propulsion mechanism. Conventional propulsors have limited maneuverability, often incapable of providing adequate torques and forces to maneuver in such environments. Elongated ribbon fin propulsion, a bio-inspired propulsion technique, can overcome these shortcomings. In the present work, we used a robotic vessel with elongated fin propulsion to test and implement three collision avoidance strategies based on potential field methods. We found that having a circular sensing envelope in the robotic vessel helps to smoothly transition to the mission path after collision is avoided. However, under this strategy, the distance to return to the desired path tends to be longer. The selection of adequate collision avoidance strategies will depend on multiple factors, including others sensing capabilities, desired reaction time, rate of turning and objects to avoid. Although this work focused on relatively simple scenarios for obstacle avoidance, we envision that utilizing more complex maneuver techniques, including rapid turns and hovering, collision avoidance strategies for underwater vessels with undulating fin propulsion can take advantage of the full fin kinematics manipulation to maneuvers as elegant as seen on the fish counterpart.