Meeting Abstract
3.5 Friday, Jan. 4 Modeling midline kinematics of fish swimming in a vortex street AKANYETI, O.*; LIAO, J. C.; The Whitney Lab for Marine Bioscience, University of Florida Gainesville; The Whitney Lab for Marine Bioscience, University of Florida Gainesville otar@whitney.ufl.edu
How fish swim in unsteady flows is hardly understood despite its strong ecological relevance. Previous kinematic studies of fish swimming in vortex streets report time-averaged measurements and lack a formal definition to capture motions on a cycle-by-cycle basis. Here we develop a model to describe the continuous body kinematics of rainbow trout (Oncorhynchus mykiss ) while Kármán gaiting behind a 5 cm diameter D section cylinder. We isolated the body bending kinematics in the fish frame of reference by subtracting the translation and rotation from the original midlines. An analysis of these transformed midlines revealed that the travelling wave equation, which has been traditionally used to model fish swimming in uniform flows, can also describe the bending of the posterior body during Kármán gaiting. We found that wave propagation along the body is a common feature between these two seemingly different behaviors, but have different characteristics. The amplitude and speed of the body wave generated by Kármán gaiting fish was 300% larger and 65% slower than for fish swimming in uniform flows. In Kármán gaiting fish the wave was initiated at the center of mass, 0.2 body lengths posterior to the initiation point for fish in uniform flows. In addition, we measured a high correlation between the lateral translation and the posterior body bending of Kármán gaiting fish (0.89±0.03, p<0.05). This suggests that the change in momentum while being buffeted side to side in the vortex street initiates the body wave. Our results show that a simple travelling wave is still a major movement strategy while navigating in unsteady flows. Whether it is generated actively through muscular activity or passively due to flow-induced motions varies depending on the flow regime.
