Date of Award

6-2018

Document Type

Thesis - SCU Access Only

Publisher

Santa Clara : Santa Clara University, 2018.

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

On Shun Pak

Abstract

With the use of synthetic micro-swimmers in biomedical applications on the rise, a fundamental understanding of low-Reynolds-number locomotion has become increasingly relevant. Despite the lack of inertia at low-Reynolds-numbers, microorganisms have evolved a variety of propulsion mechanisms that have been studied to provide insight into the design of synthetic micro-swimmers. Two features that have been identified to enable or enhance micro-scale propulsion are flexibility and non-Newtonian fluid rheology. To begin this thesis, a rigid filament attached to an oscillating torsional spring is used as a model to probe the effect of flexibility on low-Reynolds-number locomotion. Despite the scallop theorem, localized flexibility provided by the torsional spring allows for the reciprocally actuated filament to generate propulsion, demonstrating how flexibility can be exploited for propulsion at low Reynolds numbers. The second part of this thesis focuses on how non-Newtonian rheology effects the swimming of an idealized microorganism model. With the consideration of a shear-thinning fluid, expressions for the flow field and swimming speed are derived and the potential for swimming speed enhancement or reduction, as compared with the Newtonian case, is found depending on the swimming gait of the model. The reciprocal theorem is then used to find that the model has potential to swim more efficiently in a weakly shear-thinning fluid than in a Newtonian fluid. The non-trivial variations of swimming efficiency prompt questions on how microorganisms can tune their swimming gaits to exploit the shear-thinning rheology. The findings also provide insight into how synthetic micro-swimmers can be designed to move through complex media effectively. Overall, flexibility and non-Newtonian fluid rheology are found to enable and enhance locomotion at low Reynolds numbers.

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