Meeting Abstract
65.5 Thursday, Jan. 6 Ground Effects on Undulating Fins: Robotic Modeling of Stingray Locomotion BLEVINS, E.L.*; LAUDER, G.V.; Harvard University; Harvard University eblevins@fas.harvard.edu
Benthic fish are specialized for life at the boundary between the fluid and solid world. Many species use the substrate for a direct boost to propulsion, from pelvic fin punting by skates and rays to fin-walking in sharks, lungfish, and other taxa. However, even without direct contact, locomotion is influenced—and can be enhanced—by a nearby substrate, as ground effects alter fluid flow in the narrow gap between substrate and fish. These effects have been determined for static structures of various shapes, but the undulations of fish fins and bodies alter the ground effects that swimming fish experience, impacting benthic swimmers like stingrays, which undulate dorsoventrally near the substrate, and any laterally-undulating fish swimming near a wall. To determine ground effects on undulatory swimmers, we use a physical model fin (30 Shore A Neoprene) attached to a robotic flapping device with heave and pitch values from stingray kinematics. We compare the swimming performance, hydrodynamics, and cost-of-transport of fins swimming in and out of ground effect (near-substrate vs. freestream position; pair-wise comparisons), testing fins with actuated and free posterior edges across a range of frequencies (0.5, 1, 1.5 and 2 Hz). Swimming performance is defined as self-propelled swimming speed, hydrodynamics visualized via DPIV, and cost-of-transport calculated from the motor force required to move the fin (measured by ATI 6-axis force/torque transducer). For one combination of fin & kinematics (free edge, 1 Hz), a 16% speed increase occurs in the near-substrate position (p<<0.05), yet smaller or zero effects occur at other frequencies. Precise tuning of kinematics and distance from the substrate may be required for benthic fish to experience a locomotor benefit from ground effect, but substantial gains are possible.
