Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R53: Flow Driven Pattern Formation in Wet Granular Medium IInvited
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Sponsoring Units: GSNP Chair: Arshad Kudrolli, Clark University Room: BCEC 253C |
Thursday, March 7, 2019 8:00AM - 8:36AM |
R53.00001: On flow, fracture and getting jammed – Failure modes in dense suspensions Invited Speaker: Irmgard Bischofberger Dense suspensions are a class of complex fluids that exhibit both shear-thickening and shear-jamming behavior as a response to an applied stress. These dynamic liquid-to-solid transitions have important consequences for the displacement of a dense suspension by another fluid: upon the injection of air, intricate patterns arise in the suspension, leading to flow or fracture of the material. We displace a cornstarch suspension by a pressure-controlled injection of air in a quasi-2D geometry. Depending on the concentration of cornstarch and the applied stress, we observe a variety of patterns: smooth fingering in the fluid regime and different modes of fractures, ranging from slow branched cracks to single fast fractures. Remarkably, there is a regime where, despite the application of pressure, the suspension cannot be displaced. Only upon an increase to a higher pressure, air injection occurs, leading to very thin fractures in the suspension. We hypothesize that in this regime the suspension is in the shear-jammed state. This would imply a novel way of investigating the mechanical properties of a shear-jammed material by probing its fracture behavior. |
Thursday, March 7, 2019 8:36AM - 9:12AM |
R53.00002: Multiphase flow in porous media: wetting, disorder, and pattern formation Invited Speaker: Ruben Juanes The displacement of one fluid by another in a porous medium gives rise to a rich variety of hydrodynamic instabilities. Beyond their scientific value as fascinating models of pattern formation, unstable porous-media flows are essential to understanding many natural and man-made processes, including water infiltration in the vadose zone, carbon dioxide injection and storage in deep saline aquifers, methane venting from organic-rich sediments, and fracturing from fluid injection. Here, we review a handful of these hydromechanical instabilities, elucidate the key physics at play, and point to modeling frameworks that permit quantitative assessments of their impact at the geologic scale. |
Thursday, March 7, 2019 9:12AM - 9:48AM |
R53.00003: Stressing gels out: exploiting gradients in shrinkable packings Invited Speaker: Sujit Datta Diverse biological settings, ranging from actuation to drug delivery, rely on how soft gels respond to environmental stresses. In this talk, I will describe how we combine experiments and poroelasticity theory to investigate the influence of osmotic stresses in hydrogel packings. In some cases, the stresses that develop cause packings to crack. We show how cracking behavior depends on gradients in the stress profile, suggesting a way to control material behavior in this complex system. Ultimately, our work stimulates new findings and questions at the interface of Physics, Biology, Materials Science, and Engineering. |
Thursday, March 7, 2019 9:48AM - 10:24AM |
R53.00004: Granular erosion in Stokes flow Invited Speaker: Nick Moore Fluid-mechanical erosion of solid material occurs across many scales, from massive geological structures down to tiny granular constituents. Here, we numerically examine the erosion of a granular medium in the Stokes limit — the regime of groundwater flow. We combine a highly accurate boundary-integral formulation of the Stokes equations with stable interface-evolution methods. A single body erodes into a slender, for-aft-symmetric morphology which can be described analytical. Using the fast multipole method allows the simulation of 10-100 bodies. Many-body erosion naturally leads to the formation of channels and anisotropy in the medium |
Thursday, March 7, 2019 10:24AM - 11:00AM |
R53.00005: Pattern formation of frictional fingers in a gravitational potential Invited Speaker: Knut Måløy This work concerns experiments and simulations of slow drainage in a deformable quasi 2D porous media Hele Shaw. We introduce gravity as a parameter in the experiments where air displaces a liquid- granular mixture during drainage of a Hele-Shaw cell, by imposing shallow tilt angles. The receding interface accumulates a front of granular material, and an instability caused by a competition between surface tension and frictional forces results in an emerging pattern of frictional fingers, canals of air separated by branches of compacted grains, as also observed in horizontal systems. Aligned finger structures, with a characteristic width, emerge during the slow drainage. A transition from vertical to horizontal alignment of the finger structures is observed as the tilting angle and the granular density are varied. An analytical model is presented, demonstrating that the alignment properties are the result of the competition between fluctuating granular stresses and the hydrostatic pressure. The dynamics is reproduced in simulations. We also show how the system may explain patterns observed in nature, created during the early stages of a dike formation. |
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