Swarming and swirling in self-propelled polar granular rods

TL;DR

This study investigates how the shape of self-propelled granular rods influences their collective behavior, revealing unique phenomena like local ordering, wall aggregation, and persistent swirling motion not seen in spherical particles.

Contribution

It provides experimental and simulation evidence that particle shape critically affects collective dynamics in active granular systems, highlighting phenomena specific to anisotropic particles.

Findings

Shape induces local ordering and wall aggregation.

Self-propelled rods exhibit persistent swirling motion.

Spherical particles do not show these behaviors.

Abstract

Using experiments with anisotropic vibrated rods and quasi-2D numerical simulations, we show that shape plays an important role in the collective dynamics of self-propelled (SP) particles. We demonstrate that SP rods exhibit local ordering, aggregation at the side walls, and clustering absent in round SP particles. Furthermore, we find that at sufficiently strong excitation SP rods engage in a persistent swirling motion in which the velocity is strongly correlated with particle orientation.