Mud swimming: locomotion through a viscoplastic fluid

Duncan Hewitt

University College London

Abstract

Different classical models of small, slow (inertialess) swimming are considered when the ambient fluid has a yield stress. A variety of organisms inhabit and have to move through mud, mucus and other biological media, or more generally, soil and sand, all of which can exhibit viscoplastic behaviour. Basic mechanisms for inertialess swimming in ‘simple’ viscoplastic (Bingham) fluids are considered from a theoretical and numerical standpoint, with a particular focus on the role of the yield stress, the location of plugged-up regions around the swimmer’s body, and the speed and efficiency of locomotion. Taylor’s canonical ‘swimming sheet’, idealised versions of squirming organisms, and long, thin worm-like motions are all discussed, the latter of which involves a generalisation of classical slender-body theory for viscoplastic fluids.

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