Locomotion of a Scallop-Inspired Swimmer in Granular Matter

TL;DR

This study demonstrates that a scallop-inspired swimmer can move in granular matter by exploiting particle jamming and convection, challenging the traditional scallop theorem applicable to viscous fluids.

Contribution

The paper reveals how reciprocal motion can generate propulsion in granular media, contrasting with established principles in viscous fluid swimming.

Findings

Swimmer achieves locomotion in granular matter.

Propulsion results from jamming and convection effects.

Reciprocal motion can break symmetry in granular media.

Abstract

Understanding swimming in soft yielding media is challenging due to their complex deformation response to the swimmer's motion. We experimentally show that a scallop-inspired swimmer with reciprocally flapping wings generates locomotion in granular matter. This disagrees with the scallop theorem prohibiting reciprocal swimming in a liquid when its inertia is negligible. We use X-ray tomography and laser profilometry to show that the propulsion is created by the combined effects of jamming and convection of particles near the wings, which break the symmetry in packing density, surface deformation, and kinematics of the granular medium between an opening and a closing stroke.