Metachronal swimming in Antarctic krill: gait kinematics and system design |
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Authors: | D W Murphy D R Webster S Kawaguchi R King J Yen |
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Institution: | (1) School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0355, USA;(2) Australian Antarctic Division, Kingston, TAS, 7050, Australia;(3) School of Biology, Georgia Institute of Technology, Atlanta, GA 30332-0230, USA |
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Abstract: | Metachronal swimming, in which adjacent appendages stroke in sequence, is widespread among crustaceans inhabiting the transitional
flow realm in which both viscosity and inertia effects are important. However, the design and operation of this propulsion
system in response to various hydrodynamic, energetic, and behavioral needs have not been well investigated. We examine free-swimming
Antarctic krill (Euphausia superba) as a model species and identify three distinct behavioral swimming gaits. The pleopod kinematics of these gaits, hovering,
fast-forward swimming, and upside-down swimming, are quantified via image analysis of high-speed video. Pleopod stroke amplitude
and frequency were found to vary significantly among these swimming modes. In order to increase swimming speed, krill were
found first to increase stroke amplitude and secondarily to increase beat frequency. The kinematics of these distinct swimming
modes provide insight as we consider multi-appendage metachronal swimming from a design standpoint. The ratio of the distance
between adjacent appendage bases and appendage length is identified as a key parameter in metachrony, the value of which is
constrained to a narrow range for a wide variety of species. |
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