Kinematics, hydrodynamics and energetic advantages of burst-and-coast swimming of koi carps (Cyprinus carpio koi)

Abstract

Koi carps frequently swim in burst-and-coast style, which consists of a burst phase and a coast phase. We quantify the swimming kinematics and the flow patterns generated by the carps in burst-and-coast swimming. In the burst phase, the carps burst in two modes: in the first, the tail beats for at least one cycle (multiple tail-beat mode); in the second, the tail beats for only a half-cycle (half tail-beat mode). The carp generates a vortex ring in each half-cycle beat. The vortex rings generated during bursting in multiple tail-beat mode form a linked chain, but only one vortex ring is generated in half tail-beat mode. The wake morphologies, such as momentum angle and jet angle, also show much difference between the two modes. In the burst phase, the kinematic data and the impulse obtained from the wake are linked to obtain the drag coefficient (C d,burst Ϸ0.242). In the coast phase, drag coefficient (C d,coast Ϸ0.060) is estimated from swimming speed deceleration. Our estimation suggests that nearly 45% of energy is saved when burst-and-coast swimming is used by the koi carps compared with steady swimming at the same mean speed.

Hydrodynamic Performance of an Undulatory Robot: Functional Roles of the Body and Caudal Fin Locomotion

“…To explain the general trend in wake transition observed in this study, the lowest St region (0<St<0.15), the classic "Von Karman Vortex", can be observed within St<0. 15 and is denoted by region A, where the model didn't generate any thrust wake, but rather a drag wake. A slight increase in St in region B (0.15≤St≤0.325), the typical "Reverse Karman Vortex Street", was observed.…”

“…This resulted in the successful illumination of the captured area by the bright laser light sheet. We then used the 'mpiv' Matlab toolbox, which is open-source software and was successfully tested in our previous biological studies [15]. As shown in the dashed blue box in Fig.…”

“…All mechanical links were simultaneously controlled by a motion coordinator, Trio MC206. Details of the robotic swimmer's implementation were also discussed in our previous paper [15]. To study the hydrodynamic effect of the robotic swimmer as a function of the Stouhal number (St), undulatory amplitude (h), body undulatory wavelength (λ), the caudal fin pitch angle (θ) and the parameter range should be appropriately set to make the kinematics relevant to the live fish locomotion.…”

“…15. The orientation of vortices in the wake can be used to demonstrate whether thrust or drag is being produced by the bio-robotic system.…”

“…Through many studies on fish biomechanics [9], one significant technological development stands out. By seeding particles in water and shooting a laser sheet behind the swimming fish or robotic model, we were able to quantify hydrodynamic variables and flow patterns directly by using Digital Particle Image Velocimetry (DPIV) [11]- [15].…”