56.5 Thursday, Jan. 5 Undulatory locomotion by flexible foils as a model of understanding fish propulsion SHELTON, R.M.*; LAUDER, G.V.; Univ. of North Carolina, Chapel Hill firstname.lastname@example.org
Undulatory locomotion is a common method for creating thrust and maneuvering in many fish species, but our inability to experimentally manipulate key variables such as body length, flexural stiffness, and tailbeat frequency in freely-swimming fish has limited our understanding of the basic mechanics of this locomotor mode. Measuring forces and torques on a freely-swimming fish has also proven quite difficult. In this presentation we describe the use of a self-propelled robotic flapping foil apparatus to swim passive plastic foils by creating a heave motion at their leading edge. We swam foils with two different lengths, two stiffnesses, at four heave frequencies while measuring forces and torques with the flapping foil robotic device, and we simultaneously quantified swimming hydrodynamics with particle image velocimetry. When comparing the two swimming foils to bluegill sunfish (Lepomis macrochirus) and clown knifefish (Notopterus chitala), we found remarkably similar kinematics, velocities, Strouhal numbers, and patterns of curvature and shape. From the force data we calculated thrust and power coefficients, work, and costs of transport for each foil and found that increasing heave frequency and foil stiffness both produced faster swimming speeds. Increasing the foil length had minimal impact on swimming speeds, but had a large impact on Strouhal number and cost of transport. Stiffer and longer swimming foils had the lowest cost of transport (calculated in mJ m-1 g-1) at low cycle frequencies and reached the highest swimming speed at high cycle frequencies.