Control of vortex rings for manoeuvrability

Abstract

Manoeuvrability is critical to the success of many species. Selective forces acting over millions of years have resulted in a range of capabilities currently unmatched by machines. Thus, understanding animal control of fluids for manoeuvring has both biological and engineering applications. Within inertial fluid regimes, propulsion involves the formation and interaction of vortices to generate thrust. We use both volumetric and planar imaging techniques to quantify how jellyfish (Aurelia aurita) modulate vortex rings during turning behaviour. Our results show that these animals distort individual vortex rings during turns to alter the force balance across the animal, primarily through kinematic modulation of the bell margin. We find that only a portion of the vortex ring separates from the body during turns, which may increase torque. Using a fluorescent actin staining method, we demonstrate the presence of radial muscle fibres lining the bell along the margin. The presence of radial muscles provides a mechanistic explanation for the ability of scyphomedusae to alter their bell kinematics to generate non-symmetric thrust for manoeuvring. These results illustrate the advantage of combining imaging methods and provide new insights into the modulation and control of vorticity for low-speed animal manoeuvring.

Simultaneous measurement of 3D zooplankton trajectories and surrounding fluid velocity field in complex flows

“…Digital holography has been applied to track a copepod feeding current (Malkiel et al, 2003) and copepod nauplius kinematics (Gemmell et al, 2013). V3V has been used to study fish (Flammang et al, 2011) and jellyfish (Gemmell et al, 2015) locomotion. Tomographic PIV has been used to study wakes of swimming copepods (Murphy et al, 2012) and swimming Daphnia (Michaelis, 2014).…”

Organization of the subumbrellar musculature in the ephyra, juvenile, and adult stages of Aurelia aurita Medusae

“…Jellyfish also use swimming pulsations to remain upright in the water column in response to a tilt away from horizontal. Medusae of A. aurita right themselves through asymmetrical contractions of the subumbrella (Gemmell, Troolin, Costello, Colin, & Satterlie, ; Rakow & Graham, ). In tilted individuals, the contraction wave is often initiated at the portion of the medusa on the inside of the turn (Gladfelter, ; Horridge, ).…”

“…The margin in medusae of A. aurita is more flexible than the rest of the bell, and this flexibility enhances the efficiency of rowing locomotion (Colin et al, ). The ability of medusae to control this marginal flexibility contributes to the maneuverability during turns (Gemmell et al, ). In a preliminary study of subumbrellar musculature, the circular swim muscle sheet stopped short of the margin, creating a ring of tissue 0.1–0.2 mm in width, contributing to the flexible margin.…”

“…In a preliminary study of subumbrellar musculature, the circular swim muscle sheet stopped short of the margin, creating a ring of tissue 0.1–0.2 mm in width, contributing to the flexible margin. This ring of tissue contains a loose array of radial muscle cells that presumably allow active control of the flexibility of this marginal gap (Gemmell et al, ). Here we provide a detailed examination of the subumbrellar musculature of A. aurita to include the marginal gap, radial muscle, but also unexpected distortions of muscle fiber orientation within the circular muscle sheet.…”

Widespread utilization of passive energy recapture in swimming medusae

“…controlled primarily through pause duration between swimming cycles, suggests a robust principle 201 that could be applied to various types of pulsatile bio-inspired propulsive systems. There is also 202 evidence that stopping vortices formed during bell relaxation are important for maneuvering in 203 medusaeGemmell et al, 2015) and should also be considered in animal-based 204…”