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Abtahi, Seyed Arman

University of British Columbia

Both biological swimming microorganisms and artificial active particles capable of propulsion have recently been active areas of research in fluid dynamics. The influence of nearby boundaries or other active particles or swimmers is critical in many important cases for understanding various phenomena. Bacteria, for example, accumulate near surfaces and interact closely to form biofilms. Accordingly, this dissertation addresses a few gaps in the literature of microorganism hydrodynamics. First, we focus on the suspension of active particles near solid boundaries. We start with the study of the hydrodynamics of two unequal swimmers at close proximity by considering the squirming model. In comparison to passive particles, microorganisms have surface activity that provides the impetus for swimmers to move. In order to satisfy both the boundary conditions on the swimmers' skin and the Stokes equations, a regular perturbation in the velocity and pressure field of the inner creeping flow between the swimmers is employed. A relatively large size ratio leads to the hydrodynamics of a squirmer near a flat surface. Afterwards, we calculate the far-field hydrodynamics of a suspension of squirmers near a solid boundary. In the course of calculations, an extension of Stokesian Dynamics (SD) method, developed for passive particles, is utilized for active particles. This technique, called active SD, offers a good starting point for further research questions in the field. The transition between near-field and far-field solutions is also discussed. Thereafter, we propose a rigid and a flexible toy model to examine the effect of elasticity on the dynamics of a swimmer. Eventually, the developed method can help to establish a relation between hydrodynamics and biological behaviours, e.g., biofilm formation. Ultimately, we focus on axisymmetric particles in non-Newtonian fluids as a first step toward extending the SD method for poly disperse nonspherical active particles in complex fluids. We investigate the dynamics of a prolate spheroid in a shear flow of a shear-thinning Carreau fluid. The motion of a prolate particle is developed analytically for asymptotically weak shear thinning and then integrated numerically.

Text

2022-12-22

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/83480

Mechanical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/