Meeting Abstract
Unsteady aquatic locomotion is not an exception, but how animals swim most of the time. It includes fast-starts (C- or S-start), escape maneuvers, turns, acceleration/deceleration, and even during steady locomotion the swimming fluctuates, i.e., there is unsteadiness. Here a review of the recent work on unsteady aquatic locomotion with emphasis on numerical simulations is presented. First, the swimming speed’s unsteady fluctuations during straight-line swimming is reviewed, and the effect of body shape, fins, and motion on such fluctuations is discussed. These fluctuations are typically less than 3% of the average swimming speed, but recent simulations show that body shape affects fluctuations more than body kinematics, i.e., changing body shape generates larger fluctuations than changing body kinematics. Next, previous work on fast-starts and turns is reviewed, and the role of fins during such maneuvers is discussed. Recent simulations show that the kinematics during C-start is the optimum kinematics to achieve maximum acceleration. Furthermore, another set of simulations, which are validated against experimental flow measurements, investigate the role of fins during the C-start. The simulations showed that most of the force is generated by the body of the fish (not fins) during the first stage of the C-start when the fish bends itself into the C-shape. However, in the second stage, when it rapidly bends out of the C-shape, more than 70% of the instantaneous hydrodynamic force is produced by the tail. The effect of dorsal and anal fins was less than 5% of the instantaneous force in both stages, except for a short period of time (2 ms) just before the second stage. Therefore, the active control and the erection of the anal/dorsal fins might be related to retaining the stability of the sunfish against roll and pitch movements during the C-start.
