Meeting Abstract

68.2  Thursday, Jan. 6  An experimentally validated fluid dynamic model of ribbon-finned propulsion reveals how thrust is controlled by counter-propagating waves SEFATI, S.*; MITCHELL, T.; FORTUNE, E.S.; COWAN, N.J.; Johns Hopkins University; Johns Hopkins University; Johns Hopkins University; Johns Hopkins University shahin@jhu.edu

Eigenmannia virescens and other knifefish rely primarily on a long undulating ribbon fin for thrust production. In many species, the ribbon fin exhibits counter-propagating waves that originate from the rostral and caudal ends of the fin and propagate toward a more central location or “node”. This segmentation produces antagonistic thrust forces. Here we examine the role of the position of this node in the generation of net fore-aft thrust. For experiments, we placed a fish in a flow tunnel that produced constant flow speeds from 0 to 20 cm/s. Using high-speed videography, we measured the 2D kinematics of the ribbon fin as a function of flow speed and determined the wavelength, amplitude, and frequency of each counter-propagating wave. The nodal point was also identified from which the relative lengths of each wave were determined. As a function of flow speed, the nodal position shifts toward the downstream end until it saturates, resulting in a single propagating wave. Next, we developed a fluid dynamical drag model of the ribbon fin to estimate the thrust force assuming a high Reynolds number flow regime. Measured kinematic parameters, together with 3D morphological measurements, were used as inputs to the model. To validate the model, we simulated swimming of Eigenmannia using kinematic parameters of individuals and compared the net thrust predicted by the model to the experimental results. The physics-based model closely matched experimental data suggesting that the nodal position is the dominant mechanism for thrust production over the range of velocities for which the animal used counter propagating waves (up to about 10-15 cm/s). This mechanism of controlling thrust through the differential adjustment of the counter-propagating waves may simplify control for low-speed swimming.