Date of Award

12-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mathematics and Systems Engineering

First Advisor

Jian Du

Second Advisor

Venkat Keshav Chivukula

Third Advisor

Gnana Bhaskar Tenali

Fourth Advisor

Aaron Welters

Abstract

Microorganisms often swim within complex fluid environments composed of multiple materials with very different properties. Biological locomotion, including swimming speed, is significantly impacted by the physical composition and rheology of the surrounding fluid environment, as well as the presence of phase boundaries and free interfaces, across which physical properties of the fluid media may vary greatly. Through computational simulations, we first investigate the classical Taylor’s swimming sheet problem near interfaces within multi-fluid environments using a two-fluid immersed boundary method. The accuracy of the methodology is illustrated through comparisons with analytical solutions. Our simulation results indicate that the interface dynamics and phase separation in the multi-fluid mixture are closely coupled with the movement of the swimmer. Depending on the interface location, the frictional coefficient, and the multi-fluid composition, the swimmer can move either faster or slower than that in a single-phase fluid. Furthermore, we investigate the movement of a finite-length undulatory swimmer near interfaces within a viscous two-fluid media. Our simulation results show that significant speed-ups can be achieved only if the active swimmer has a large body elasticity.

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