Migration, trapping, and venting of gas in a soft granular material

Gas migration through a soft granular material involves a strong coupling between the motion of the gas and the deformation of the material. This process is relevant to a variety of natural phenomena, such as gas venting from sediments and gas exsolution from magma. Here, we study this process experimentally by injecting air into a quasi-2D packing of soft particles and measuring the morphology of the air as it invades and then rises due to buoyancy. We systematically increase the confining pre-stress in the packing by compressing it with a fluid-permeable piston, leading to a gradual transition in migration regime from fluidization to pathway opening to pore invasion. We find that mixed migration regimes emerge at intermediate confinement due to the spontaneous formation of a compaction layer at the top of the flow cell. By connecting these migration mechanisms with macroscopic invasion, trapping, and venting, we show that mixed regimes enable a sharp increase in the average amount of gas trapped within the packing, as well as much larger venting events. Our results suggest that the relationship between invasion, trapping, and venting could be controlled by modulating the confining stress

A two-dimensional model of low-Reynolds number swimming beneath a free surface

Biological organisms swimming at low Reynolds number are often influenced by the presence of rigid boundaries and soft interfaces. In this paper we present an analysis of locomotion near a free surface with surface tension. Using a simplified two-dimensional singularity model, and combining a complex variable approach with conformal mapping techniques, we demonstrate that the deformation of a free surface can be harnessed to produce steady locomotion parallel to the interface. The crucial physical ingredient lies in the nonlinear hydrodynamic coupling between the disturbance flow created by the swimmer and the free boundary problem at the fluid surface

Biolocomotion near free surfaces in Stokes flows : mechanism of swimming and optimization

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 105-[111]).Locomotion of biological systems have fascinated physicists and engineers alike for centuries. In particular, we are interested in the motion of self-propelling bodies near an air-water interface in the low Reynolds number limit. To investigate this problem, we take two very different approaches. We first consider the locomotion of a specific organism, namely, a water snail, that exhibits a striking ability to "crawl" beneath the free surface. By modeling the foot of the snail as undergoing a simple sinusoidal motion, we apply lubrication approximations for small deformations to rationalize this peculiar mode of transport and its dependency on surface tension. Inspired by this study, the second part of my thesis focuses on the general two-dimensional model of an organism that utilizes a free surface to propel itself. Based on conformal mapping techniques, we are able to derive exact solutions describing the highly nonlinear coupling between the motion of the swimmer and the free surface deformations, without putting any limits on the deformation size. These closed-form solutions are then applied to optimization questions. In the high Reynolds number limit, swimming near the free surface is known to increase drag on the swimmer due to the cost associated with creating surface waves. However, we find that, for a low Reynolds number swimmer that utilizes the free surface to move, a different power law relation between the distance from the interface and the swimming efficiency exists, implying that the presence of the free surface can be beneficial in certain parameter regimes.by Sungyon Lee.Ph.D

Galerkin method to model thin free surface flows

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 65-68).Viscoelastic thin films with free surface are important in industry as well as in nature. However, there does not exist a robust and systematic framework to analyze such films. Lubrication approximations, largely successful in studying thin generalized Newtonian fluid flows, have been employed to tackle this task but have met with only limited success. This particular work highlights the shortcomings of the lubrication analysis in this context and suggests an alternative in the form of a Galerkin-like projection method.by Sungyon Lee.S.M

Programming droplet motion using metamaterials

Motion control of droplets has generated much attention for its applications to microfluidics, where precise control of small fluid volumes is an imperative requirement. Mechanical vibrations have been shown to be effective at inducing controllable depinning, and activation of different drop motion regimes. However, existing vibration-based strategies involve establishing homogeneous rigid-body dynamics on the substrate, and therefore lack any form of spatial heterogeneity and tuning. Addressing this limitation, metamaterials provide an ideal platform to achieve spectrally and spatially selective drop motion control, which leverages their ability to attenuate vibrations in selected frequency bands and in selected regions of a substrate. In this work, we illustrate the potential of metamaterials-based drop control by experimentally demonstrating a variety of drop motion capabilities on the surface of metaplates endowed with locally resonant stubs. The experiments leverage the design versatility of a LEGO component-enabled reconfigurable design platform and laser vibrometry measurements with high spatial resolution

Experimental investigation of bidensity slurries on an incline

We investigate the dynamics of bidensity slurries on an incline. The particle-fluid mixture consists of two species of negatively buoyant particles that have roughly the same size but significantly variant densities. This mismatch in particle densities induces or prevents settling depending on the relative amount of heavy to light particles, leading to complex regimes also found in the monodisperse case. In addition, when settling effects dominate within the thin film, we observe the phase separation down the incline between the particles and the liquid, as well as between two particle types. © 2014 Springer-Verlag Berlin Heidelberg

Particles & Interfaces

Non UBCUnreviewedAuthor affiliation: Texas A&M UniversityFacult