Simulation of swimming oblate jellyfish with a paddling-based locomotion

Abstract

The hydrodynamics of a swimming jellyfish depends on the morphology of the species. For example, oblate jellyfish appear to generate wide vortex structures near the bell margin. The vortex structures affect both the propulsion system and the feeding structure because the swimming and prey capturing activities are interrelated processes in these taxa. A three-dimensional computational model was established for an oblate jellyfish to analyse how the vortex structures present in the wake affect the swimming mechanism and the propulsion efficiency, which is defined as the ratio of power output (thrust multiplied by centre velocity) to power input (energy rate required for bell contraction). An improved penalty immersed boundary method was adopted to consider the interactions between the swimming jellyfish and the ambient fluid. The vortex structures in the wake of the swimming jellyfish were investigated in detail. The vortices generated by the contraction and expansion of the jellyfish bell interact with the vortex structures generated by the forward-moving behaviour of the jellyfish. The resulting vortex structures not only transfer momentum to the swimming jellyfish via the fluid, thereby providing the main source of thrust, but also have an implication for feeding. The effects of the elastic properties of the jellyfish on the propulsion were examined. The propulsion efficiency reaches its optimum value at particular elastic properties. We also investigated the effect of the swimming pattern of jellyfish on the propulsion efficiency. The efficiency increases with the flapping frequency and force duration.

Dynamics of prolate jellyfish with a jet-based locomotion

“…The bell contraction in a prolate jellyfish generally proceeds along the bell, whereas the bell contraction in an oblate jellyfish only occurs near the bell margin (Ford and Costello, 2000). In Park et al (2014) for an oblate swimming jellyfish, the body force was applied over the bell range of approximately 33% from the bell margin. In the present prolate jellyfish, the body force was applied along the inside of the bell when the distance between the bell tip and the forcing points is less than 0.5, which occupies approximately 50% of the arc length of the bell.…”

“…An appropriate swimming pattern was chosen by jellyfish according to circumstances such as traveling, fishing, or escaping (Megill, 2002;Mills, 1981;Park et al, 2014). Many dynamic models have been proposed for predicting the kinematics of swimming jellyfish (Daniel, 1985;Colin and Costello, 2002), although the hydrodynamics in the wake has not been considered in these models.…”

“…By using the immersed boundary method (Peskin, 2002), Herschlag and Miller (2011) used the bell model of a simplified jellyfish and investigated the effective limits of jet propulsion in terms of the Reynolds number. Park et al (2014) adopted an immersed boundary method to elucidate the hydrodynamics in the wake and the propulsion kinematics of an oblate jellyfish implementing a paddling-based locomotion. The thrust-generating mechanisms in both prolate and oblate jellyfish were investigated by using the arbitrary Lagrangian-Eulerian (ALE) formulation (Sahin and Mohseni, 2009;.…”

Hydrodynamics of a self-propelled flexible fin in perturbed flows

“…Many animals have their own propulsion mechanisms, and specific hydrodynamic patterns are generated in the wake of these animals, depending on their flapping behaviors (Park et al 2014). The hydrodynamic footprints result from interactions between the animal bodies and the surrounding fluid.…”

Vortex interaction between two tandem flexible propulsors with a paddling-based locomotion

“…Although jellyfish are jet-based propelling animals, a relatively small subset of jellyfish created a single vortex structure during a flapping cycle similar to the vortex structures produced by other animals during propulsion through jet-based locomotion (Dabiri 2009). Many species generate different sets of vortical structures through the contraction and relaxation of the bell, and they interact with one another through a complicated mechanism (Colin & Costello 2002;Dabiri 2005;Park et al 2014). Starting and stopping vortical structures were found to be generated during the contraction and relaxation phases, respectively, and the vortex induced motions in the surrounding fluid that were interrelated with the propulsion and feeding mechanisms (Colin & Costello 2002;Mchenry & Jed 2003;Dabiri et al 2005;Sahin, Mohseni & Colin 2009;Park et al 2014).…”