Controlled fluid transport by the collective motion of microrotors

TL;DR

This paper develops a simulation-based optimal control framework for guiding fluid transport using groups of microrotors, leveraging polynomial chaos and flow structure analysis to improve biomedical micro-manipulation.

Contribution

It introduces a novel control approach combining polynomial chaos modeling and flow analysis to steer fluid particles with microrotors, addressing a key challenge in microscale fluid manipulation.

Findings

Successful simulation of controlled fluid transport to target locations.

Identification of transport barriers via Lagrangian coherent structures.

Effective control strategies for rotor velocities and torques.

Abstract

Torque-driven microscale swimming robots, or microrotors, hold significant potential in biomedical applications such as targeted drug delivery, minimally invasive surgery, and micromanipulation. This paper addresses the challenge of controlling the transport of fluid volumes using the flow fields generated by interacting groups of microrotors. Our approach uses polynomial chaos expansions to model the time evolution of fluid particle distributions and formulate an optimal control problem, which we solve numerically. We implement this framework in simulation to achieve the controlled transport of an initial fluid particle distribution to a target destination while minimizing undesirable effects such as stretching and mixing. We consider the case where translational velocities of the rotors are directly controlled, as well as the case where only torques are controlled and the rotors move in response to the collective flow fields they generate. We analyze the solution of this optimal control problem by computing the Lagrangian coherent structures of the associated flow field, which reveal the formation of transport barriers that efficiently guide particles toward their target. This analysis provides insights into the underlying mechanisms of controlled transport.