Swimming the Chaotic Seas: Invariant Manifolds, Tori, and the Transport of Swimmers in Fluid Flows

University Of California - Merced, Merced CA

Investigators

Abstract

The dynamics and control of self-propelled bodies, from swarms of autonomous underwater vehicles (AUVs) and fish schools to populations of swimming bacteria, are of great interest to biophysics and engineering. Yet, while much work has focused on the collective behavior arising from interactions between individuals, less is known about the dynamics of these individuals in external, dynamically changing environments. This research will tackle the fundamental question of how isolated, self-propelled swimmers are transported in unsteady fluid flows. By leveraging tools from dynamical systems theory, such as those used in analyzing the propagation of reaction fronts in fluid flows, this project aims to create better understanding of the behavior of swimmers moving in realistic flows in nature and the laboratory. This work will educate and train the next generation of the scientific work force and will greatly impact the growth and educational mission of UC Merced, a university that was recently established in one of California's most economically challenged areas. Stable and unstable manifolds are critical structures that control the transport and mixing of passive particles in steady, time-independent flows. These manifolds both partition the fluid into vortex cells and control the transport between cells via “turnstile” lobes in the fluid. Lagrangian coherent structures (LCSs) provide an analogous framework in unsteady, aperiodic flows. The objective of this project is to adapt these theories to particles that are both advected by the fluid and propelled under their own power. Invariant manifolds and passive LCS are no longer the most relevant structures. Rather, swimming invariant manifolds (SwIMs), which depend explicitly on the swimming speed, along with SwIM edges and invariant tori, form key structures in the phase space. This research will: (i) investigate the role of these structures in both trapping swimmers and generating ballistic motion, (ii) explore the role of SwIMs on restricting and guiding transport in chaotic environments, (iii) develop a rigorous approach to account for swimmer noise in vortex flows, and (iv) connect these ideas to real-world organisms and flows through collaborations with experimentalists that study the transport of bacteria and algae in microfluidic flows. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.