Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session M29: Focus Session: Wet Granular Material: Capillary Aggregation to Shaping of Landscapes |
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Sponsoring Units: GSNP Chair: Arshad Kudrolli, Clark University Room: 337 |
Wednesday, March 20, 2013 8:00AM - 8:12AM |
M29.00001: Dynamics of failure in 2d granular packings Jennifer Rieser, Yuka Takehara, Wenbin Li, Ju Li, Jerry Gollub, Douglas Durian We explore the grain-scale interactions that precede large-scale deformations and mark the onset of mechanical failure in two-dimensional granular packings. The two-dimensionality of the system allows for direct observation of all particle dynamics during the compression of a pillar. The grains are cohesive, with an attraction governed by tunable capillary forces that are induced through an interstitial fluid. We are particularly interested in the initial deformation of the pillar. Here we characterize local structure and dynamics leading up to the first large-scale event. For our analysis, we focus on how local structure within the packing relates to local dynamics and eventually to large-scale deformation. Local structure and rearrangements are characterized by information from a Delaunay triangulation, and are compared with larger-scale deformations identified by spatial variations in the velocities of the particles. We explore the the effects of pillar size and cohesion strength on the dynamics in both ordered and disordered packings. [Preview Abstract] |
Wednesday, March 20, 2013 8:12AM - 8:24AM |
M29.00002: Compaction dynamics of wet granular packings Nicolas Vandewalle, Francois Ludewig, Jorge E. Fiscina, Geoffroy Lumay The extremely slow compaction dynamics of wet granular assemblies has been studied experimentally. The cohesion, due to capillary bridges between neighboring grains, has been tuned using different liquids having specific surface tension values. The characteristic relaxation time for compaction $\tau $ grows strongly with cohesion. A kinetic model [1], based on a free volume kinetic equations and the presence of a capillary energy barrier (due to liquid bridges), is able to reproduce quantitatively the experimental curves. This model allows one to describe the cohesion in wet granular packing [2]. The influence of relative humidity (RH) on the extremely slow compaction dynamics of a granular assembly has also been investigated in the range $20\%-80\%$. Triboelectric and capillary condensation effects have been introduced in the kinetic model. Results confirm the existence of an optimal condition at $\rm{RH} \approx 45\%$ for minimizing cohesive interactions between glass beads [3]. References : [1] F.Ludewig, S.Dorbolo, T.Gilet, and N.Vandewalle, EPL 84, 44001 (2008) [2] J.E.Fiscina, G.Lumay, F.Ludewig and N.Vandewalle, Phys. Rev. Lett. 105, 048001 (2010) [3] N.Vandewalle, G.Lumay, F.Ludewig, J.E.Fiscina, Phys. Rev. E 85, 031309 (2012) [Preview Abstract] |
Wednesday, March 20, 2013 8:24AM - 8:36AM |
M29.00003: Self-assembled granular towers Felipe Pacheco-Vazquez, Florian Moreau, Nicolas Vandewalle, Stephan Dorbolo When some water is added to sand, cohesion among the grains is induced. In fact, only 1{\%} of liquid volume respect to the total pore space of the sand is necessary to built impressive sandcastles. Inspired on this experience, the mechanical properties of wet piles and sand columns have been widely studied during the last years. However, most of these studies only consider wet materials with less than 35{\%} of liquid volume. Here we report the spontaneous formation of granular towers produced when dry sand is poured on a highly wet sand bed: The impacting grains stick on the wet grains due to instantaneous liquid bridges created during the impact. The grains become wet by the capillary ascension of water and the process continues, giving rise to stable narrow sand towers. Actually, the towers can reach the maximum theoretical limit of stability predicted by previous models, only expected for low liquid volumes. [Preview Abstract] |
Wednesday, March 20, 2013 8:36AM - 9:12AM |
M29.00004: Building towers, domes, and arches by self-organized solidifying flows Invited Speaker: Julien Chopin We demonstrate that a wide variety of delicate solid structures from slender towers to arches, and chiral pagodas can be created by simply pouring a mixture of grains and water on a liquid absorbing substrate [Phys. Rev. Lett. 107, 208304 (2011)]. The same suspension poured on a solid substrate would form a featureless puddle or a pile with an angle of repose. However, an absorbing substrate can quickly drain the liquid from the suspension, rapidly causing the solidification of the fluid into a mechanically stable structure. In a dripping regime, successive drops are observed to jam rapidly upon impact literally stacking on top of each other forming slender granular towers. In a jetting regime and using a moving substrate, the jet is found to bounce on and off the substrate forming regular arches. We will discuss the subtle interplay of the incoming flux of the granular suspension, the drainage efficiency of the substrate, and the mechanical properties of the solid structure. The drainage driven jamming of granular suspensions gives a new route to shape cohesive granular materials and, from a broader perspective, demonstrates the potential a solidifying fluid spreading on a substrate to create new morphologies harder to achieve by other techniques. Applications to surface patterning, rheology of dense suspension and mechanics of wet granular materials will be discussed. [Preview Abstract] |
Wednesday, March 20, 2013 9:12AM - 9:24AM |
M29.00005: Capillary fracturing in granular media Michael Szulczewski, Ran Holtzman, Mathias Trojer, Ruben Juanes The invasion of gas into liquid-saturated, deformable porous media occurs in many processes including gas venting, hydrocarbon recovery, and geologic CO$_2$ sequestration. While fracturing during gas invasion has been observed in several studies, the underlying mechanisms and macroscopic patterns remain poorly understood. Here, we experimentally investigate the fracturing mechanism and resulting patterns during the invasion of air into a thin bed of water-saturated glass beads. The control parameters are the air injection rate, the bead size, and the vertical confining stress applied to the top of the bed. We identify three invasion regimes: capillary fingering, viscous fingering, and ``capillary fracturing,'' where capillary forces overcome frictional resistance and induce the opening of fracture-like conduits. We show that the transitions between the regimes are governed by a modified capillary number and a fracturing number. We then extend the experiments to investigate the effect of wettability. Our analysis predicts the emergence of fracturing in fine-grained media under low confining stress, a phenomenon that likely plays a fundamental role in many natural systems. [Preview Abstract] |
Wednesday, March 20, 2013 9:24AM - 9:36AM |
M29.00006: Diffusive evolution of experimental river channel networks Meredith Reitz, Douglas Jerolmack, Eric Lajeunesse, Angela Limare, Olivier Devauchelle, Francois Metivier Braided rivers are complex systems in which a network of ephemeral, interacting channels continually migrate to create a rapidly changing landscape. We present results of a set of $\sim$ 1m-scale experiments of braided rivers forming over a bed of monodisperse glass beads. The experiments evolve from an initial flat bed, allowing us to study the approach to a steady state, with data in the form of repeat high-resolution topography scans. We find that, although channels migrate rapidly, they have stable, self-similar geometries organized to a critical Shields stress criterion. Above the individual channel scale, we find that we can directly describe many aspects of the system with a diffusional framework. The timescale to equilibrium slope, the timescale of decorrelation of the channel network, the rate at which downstream correlation lengthscales increase, and the dependence of the equilibrium slope on sediment flux can all be described with diffusivities that are consistent with a theoretical prediction. The emergent picture of our braided river system is one in which sediment transport drives the interaction of dynamic but equilibrium channels, which in turn act as elements of randomness that create diffusive behavior at the system scale. [Preview Abstract] |
Wednesday, March 20, 2013 9:36AM - 9:48AM |
M29.00007: A converging granular flow driven by fluid drag Steven Meier, David Yale, Arnold Kushnick, Paul Chaikin, Eric Herbolzheimer The dynamics of granular flows are known to depend on applied confining stresses and the need for the material to dilate when subjected to a shearing motion, as has been shown by studies on free-surface flows driven by gravity and confined flows driven by a moving boundary.~ Here, we present an experimental study at the 2 meter scale of a granular flow subject to a confining stress driven by fluid drag as is encountered in some petroleum recovery and geologic processes.~ Before the particles start to flow, a Darcy's law pressure gradient is generated by fluid flow.~ The onset of flow, or failure, is history dependent.~ That is, it depends on both the stress state and the particle concentration as a result of the history of deformation applied to the material.~~~ The particles begin to flow when the pressure gradient exceeds the friction due to the confining stress and the gradient of stress along the flow direction.~ The flow also depends on the ability of the granular material to dilate.~ We will show that converging flow conditions allow for this required dilation.~ Once the particles are flowing, the pressure gradient is proportional to the confining stress on the moving sand rather than on the fluid flow rate. [Preview Abstract] |
Wednesday, March 20, 2013 9:48AM - 10:00AM |
M29.00008: Rainwater Channelization and Infiltration in Granular Media Cesare Mikhail Cejas, Yuli Wei, Remi Barrois, Douglas J. Durian, Remi Dreyfus We investigate the formation of fingered flow in dry granular media under simulated rainfall using a quasi-2D experimental set-up composed of a random close packing of mono-disperse glass beads. We determine effects of grain diameter and surface wetting properties on the formation and infiltration of water channels. For hydrophilic granular media, rainwater initially infiltrates a shallow top layer of soil creating a uniform horizontal wetting front before instabilities occur and grow to form water channels. For hydrophobic media, rainwater ponds on the soil surface rather than infiltrates and water channels may still occur at a later time when the hydraulic pressure of the ponding water exceeds the capillary repellency of the soil. We probe the kinetics of the fingering instabilities that serve as precursors for the growth and drainage of water channels. We also examine the effects of several different methods on improving rainwater channelization such as varying the level of pre-saturation, modifying the soil surface flatness, and adding superabsorbent hydrogel particles. [Preview Abstract] |
Wednesday, March 20, 2013 10:00AM - 10:12AM |
M29.00009: Characterizing shear-flow-driven erosion of granular beds Julia Salevan, Mark Shattuck, Corey O'Hern, Nicholas Ouellette The complex interactions between granular media and flowing fluid play a principal role in shaping landscapes via erosion. Despite a large body of work in granular materials and large scale topographical changes in granular beds due to fluid flow, the detailed physical mechanisms that underlie particle entrainment into a fluid flow from an erodible bed and the coupling between hydrodynamic shear and internal rearrangement remain poorly understood. To address these questions, we perform experimental studies of pulsed shear flow across granular beds. We characterize the fluid flow using particle tracking techniques and monitor changes in the structural properties of the granular packing and contour of the granular bed. [Preview Abstract] |
Wednesday, March 20, 2013 10:12AM - 10:24AM |
M29.00010: River deltas: channelizing sandpiles with memory Douglas Jerolmack, Meredith Reitz River deltas are wedges of sediment that are built via the lateral migration of self-channelizing rivers, but the timescale of this process is prohibitively long to observe in nature. Here we present laboratory results that allow us to examine how channels form and fill space to create a delta. Flow collapses into a single channel whose dimensions adjust to threshold transport conditions for the imposed sediment load. This channelization causes localized shoreline growth until the slope drops below a threshold value for sediment transport. This leads to deposition within the channel, with an upstream-migrating step akin to a stopping front in granular flows, which causes widespread flooding and the selection of a new (steeper) channel path. This cycle is remarkably periodic; delta slope oscillates between two thresholds - entrainment and distrainment - analogous to static and dynamic angles of repose. Selection of a new flow path is inherently stochastic, but previously abandoned channels act as significant attractors for the flow. Once a critical density of flow paths has been established, the flow oscillates among the same 3-5 channels indefinitely. These dynamics result in self-similar (quasi-)radial growth of delta lobes, which can be described using a simple geometric model. Despite its simplicity, the experimental system agrees well with what can be measured from natural deltas Thus, temporal and spatial patterns of deltas appear to be a robust result of mass conservation and transport thresholds. [Preview Abstract] |
Wednesday, March 20, 2013 10:24AM - 10:36AM |
M29.00011: Effect of moisture content on nest construction activity of fire ants Daria Monaenkova, Nickolas Gravish, Daniel Goldman, Michael Goodisman Large underground nests protect ants from severe weather and predators. Field observations have revealed that the soil wetness affects the nest building activity. In this work we use x-ray computed tomography to study the growth of fire ants nests as a function of soil moisture content. Because capillary cohesion in wet soils leads to the competition between tunnel stability and the labor-intensity of the excavation, we expect to find an optimal soil wetness, which allows the most effective nest construction. We prepared digging containers (3.8 cm diameter by 14.5 cm deep aluminum tubes) with 2 types of simulated soil (50 and 210 um glass particles). The prepared moisture content W varied from 0.01 to 0.18 by mass. Hundred ants were allowed to dig in the containers for 20 hours. Although, the ants were able to construct tunnels in all moisture levels, the maximum tunnel depth, H, was significantly affected by W. At moderate moisture content (W$=$0.1) H was at least twice greater than at the lowest moisture content (W$=$0.01) for all tested colonies (n$=$9) for both particle sizes. The increase in H mirrors the dependence of the soil cohesion on W and we therefore conclude that the tunnel stability is a key factor influencing the digging strategy of fire ants. [Preview Abstract] |
Wednesday, March 20, 2013 10:36AM - 10:48AM |
M29.00012: Role of Surface Tension in Magnetorheological Adhesion Carlos Orellana, Heinrich Jaeger Magnetorheological (MR) fluids are colloidal suspensions of magnetizable particles that show an increment the yield stress and in the apparent viscosity in the presence of a magnetic field. It has been shown previously that MR fluids can be used for field-controlled static adhesion to non magnetic surfaces. Here we demonstrate the important role the surface tension plays in this adhesion effect (for a low viscosity carrier fluid) and that the adhesive property is not related to the field-dependent yield stress. [Preview Abstract] |
Wednesday, March 20, 2013 10:48AM - 11:00AM |
M29.00013: Shear thickening oscillation in a dilatant fluid Shin-ichiro Nagahiro, Hiizu Nakanishi, Namiko Mitarai We report experimental observations of the shear thickening oscillation; spontaneous macroscopic oscillation in the shear flow of severe shear thickening fluids. Using a phenomenological fluid dynamics model for dilatant fluids, we have been predicted theoretically that a dilatant fluid under constant shear stress oscillates due to the shear thickening property coupled with the fluid dynamics. However, such a macroscopic oscillation has never been reported in the literature. In this presentation, we report that strong vibrations of the frequency around 20 Hz is observed using a density-matched starch-water mixture, in the cylindrical shear flow of a few centimeters flow width. The oscillation behavior is consistent with the theoretical prediction. [Preview Abstract] |
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