Fluid structure interactions of soft solids and complex fluids.

Das, Asimanshu

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Year:: 2022
Contributor:: Das, Asimanshu (creator); Zenit, Roberto (Advisor); Harris, Daniel (Reader); Wilhemus, Monica (Reader); Tang, Jay (Reader); Brown University. Engineering: Fluids and Thermal Sciences (sponsor)
Genre:: theses
Subject:: Fluid Dynamics; Bacteria; Turbulence; Swimming
Extent:: xxviii, 141 p.

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Abstract:: Biological locomotion spans a wide range of length and time scales. We can draw inspiration from natural flyers and swimmers at micro and macroscopic scales. The Reynolds number used to unify these can range from 0.0001 to $10^5$. Animals, including fish, whales, dolphins, birds, bats, and insects, use appendages (fins and wings) with varying levels of flexibility and compliance to generate propulsion or weight support as they move through fluids such as air and water. Scientists have explored many aspects of natural swimming and flying, such as flapping and flexibility effects, to understand the underlying physical mechanisms and apply them to engineering applications. Compliant membrane wings of bats, flying squirrels, lemurs, and other animals fall into one class of flexible aerodynamic structures. Soft elastomeric materials also form an essential ingredient in bio-inspired engineering today, owing to their capacity for electrical actuation (dielectric), tunability of mechanical response, and resemblance to organic tissues. There has been a recent resurgence of interest in microorganism propulsion mechanisms due to the fascinating variability in their evolutionary adaptations. Bacteria have experienced enhanced speed and trajectories with less wobbling of the tail, exploiting the elastic properties of the fluid. This proposed dissertation presents a combined experimental and theoretical exploration of the i) unsteady fluid-structure interactions of an ultrasoft, elastic material in a fluid flow and ii) a swimming rheometer in an elastic fluid. The first problem provides simultaneous measurements of the deformations, forces, and flow fields to reveal the conditions for the onset of resonance, including flow modulations, as well as features leading to lift enhancement and power production using elastic shape morphings. After presenting an in-depth study on fluid-structure interactions at moderate to high Reynolds numbers, the dissertation shifts towards motility at low Reynolds number settings. The second work also aims to understand the dynamics of microbial swimming using a torque-free robot that closely emulates the swimming environments of actual bacteria in viscous and elastic fluids by conducting experiments at macroscopic scales but by employing viscous and elastic Boger fluids. Furthermore, it aims to extend to explain the effect of the geometry of helical flagella on swimming efficiency. Many previous studies create a need to understand the elastic effects of fluids to gain insights into the increased swimming efficiency and decreased wobbling due to the presence of polymers in the fluid. Movement and flow measurements around self-propelled swimmers in viscous and elastic fluids reveal insights into the scaling with swimming speeds with helix angles and new, stable configurations. In Chapter 3 of the thesis, the near field flow developing around the swimmer is mapped for viscous and elastic fluids, and the emergence of wake flows in elastic fluids with improved swimmer performance is discussed. The experiments provide insights into understanding predator-prey interactions and complex biofluid dynamics of flagellar microorganisms. The thesis also bridges the gap in the FSI in the presence of elastic solids and elastic fluids and, therein, sheds light on the implications of such interactions on flow modulation, energy extraction, lift production, and swimming efficiency.
Notes:: Thesis (Ph. D.)--Brown University, 2022

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Citation

Das, Asimanshu, "Fluid structure interactions of soft solids and complex fluids." (2022). Fluid, Thermal, and Chemical Processes Theses and Dissertations. Brown Digital Repository. Brown University Library. https://repository.library.brown.edu/studio/item/bdr:ef8kz252/

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Fluid, Thermal, and Chemical Processes Theses and Dissertations

Theses and Dissertations for the Fluid, Thermal, and Chemical Processes department.
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