Dynamical response of a system of passive or active swimmers to time-periodic forcing

TL;DR

This paper investigates how passive and active swimmer suspensions respond to time-periodic boundary forcing, revealing different behaviors depending on the driving speed and activity level, with implications for energy storage and dissipation.

Contribution

It introduces a minimal model analyzing the linear response of active and passive suspensions to time-dependent boundary forcing, highlighting novel behaviors in rapidly driven active systems.

Findings

Active systems respond similarly to passive ones under slow driving.

Rapid driving alters the motoring activity of active particles.

Response functions relate to energy storage and dissipation.

Abstract

The presence of active forces in various biological and artificial systems may change how those systems behaves under forcing. We present a minimal model of a suspension of passive or active swimmers driven on the boundaries by time-dependent forcing. In particular, we consider a time-periodic drive from which we determine the linear response functions of the suspension. The meaning of these response functions are interpreted in terms of the storage and dissipation of energy through the particles within the system. We find that while a slowly driven active system responds in a way similar to a passive system with a re-defined diffusion constant, a rapidly driven active system exhibits a novel behavior related to a change in the motoring activity of the particles due to the external drive.