Meeting Abstract

80.7  Monday, Jan. 6 11:45  Active modulation of bluegill sunfish tail compliance SETH, D; TANGORRA, J*; FLAMMANG, B.E.; LAUDER, G.V.; Drexel University, Philadelphia, PA; Drexel University, Philadelphia, PA; Harvard University, Cambridge, MA; Harvard University, Cambridge, MA tangorra@coe.drexel.edu

The goal of the study is to understand the active changes in the mechanical compliance of the bluegill sunfish (Lepomis macrochirus) tail during natural swimming. Several previous studies have investigated the relationship between body stiffness and swimming speed using dead fish and model fish. However no studies have been conducted on live fish in which the tail may be actively stiffened during swimming. The tails of bluegill sunfish (N=2, 45 trials total) were perturbed with a fluidic pulse as the fish swam at speeds of 0, 0.5, 0.65, 1.1, 1.25, and 1.5 body lengths per second (BL/s). A vortex generator was developed in-house to produce vortex pulses of controllable properties to perturb the tail. High speed video and particle image velocimetry were used to measure deflection of the fish tail and to quantify the strength of the vortex. The compliance analysis was conducted within 20ms of the perturbation’s impact to minimize the effect of active or reflexive motions. Relative compliance was calculated by comparing passive deflections in the tail at different swimming speeds. A parallel study was conducted on flapping foils of different known flexibilities to help characterize the impact of the vortex and to compare the response of the biological tail to that of a purely passive material. The results suggest a decrease in compliance of the tail as swimming speed increases. Deflections in the tail at swimming speeds below 0.65BL/s were much larger than the deflections at swimming speeds above 1.1BL/s. The results suggest that fish tune the tail’s compliance during swimming. These studies are the first conducted on live fish and support those conducted on dead and model fish.