Synchronised Swimming of Two Fish

TL;DR

This study uses two-dimensional fluid dynamics simulations to explore how synchronized swimming between two fish-like bodies can reduce energy expenditure and improve efficiency, highlighting flow interactions and adaptive behaviors.

Contribution

It introduces a novel analysis of synchronized fish swimming, demonstrating energy savings and efficiency gains through flow-mediated interactions and reinforcement learning-based coordination.

Findings

Up to 30% reduction in energy expenditure for the follower.

20% increase in swimming efficiency for the follower.

Flow interactions can lead to drag reduction and intermittent thrust generation.

Abstract

We study the fluid dynamics of two fish-like bodies with synchronised swimming patterns. Our studies are based on two-dimensional simulations of viscous incompressible flows. We distinguish between motion patterns that are externally imposed on the swimmers and self-propelled swimmers that learn manoeuvres to achieve certain goals. Simulations of two rigid bodies executing pre-specified motion indicate that flow-mediated interactions can lead to substantial drag reduction and may even generate thrust intermittently. In turn we examine two self-propelled swimmers arranged in a leader-follower configuration, with a-priori specified body-deformations. We find that the swimming of the leader remains largely unaffected, while the follower experiences either an increase or decrease in swimming speed, depending on the initial conditions. Finally, we consider a follower that synchronises its motion so as to minimise its lateral deviations from the leader's path. The leader employs a steady gait while the follower uses a reinforcement learning algorithm to adapt its swimming-kinematics. We find that swimming in a synchronised tandem can yield up to about 30% reduction in energy expenditure for the follower, in addition to a 20% increase in its swimming-efficiency. The present results indicate that synchronised swimming of two fish can be energetically beneficial.