Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session M1: Granular Flows: Impact and Force Transmission |
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Chair: Parisa Mirbod, Clarkson University Room: 3000 |
Tuesday, November 25, 2014 8:00AM - 8:13AM |
M1.00001: High-speed granular flows around a cylindrical obstacle Joshua S. Caplan, Stuart B. Dalziel, Jim N. McElwaine, Nathalie M. Vriend Geophysical granular flows are extremely destructive, but their behavior when they impact on obstacles in their path is still poorly understood. In this talk we will present the results of a series of experiments where we consider the granular flow around a cylindrical obstacle, extending previous work by Cui and Gray (2013). By using a unique recirculating chute, we are able to consider flows of up to 20~kg~s\textsuperscript{-1} at speeds of several meters per second. This gives us access to flow regimes that could not be previously considered. As has been previously observed, we find a large bow shock ahead of the obstacle and a granular vacuum behind it. We, however, find that the shock shapes are significantly different to previous observations. We will also be presenting PIV measurements of the surface velocity, height profiles of the flow, and measurements of the forces on the obstacle. [Preview Abstract] |
Tuesday, November 25, 2014 8:13AM - 8:26AM |
M1.00002: Granular Impact at High Mach Number Abe Clark, Yue Zhang, Lou Kondic, R.P. Behringer How do dynamic stresses propagate in granular material after a high-speed impact? This occurs often in natural and industrial processes. Stress propagation in a granular material is controlled by the inter-particle force law, $f$, in terms of particle deformation, $\delta$, often given by $f\propto\delta^{\alpha}$, with $\alpha>1$. This means that a linear wave description is invalid when dynamic stresses are large compared to the original confining pressure. With high-speed video and photoelastic grains with varying stiffness, we experimentally study how forces propagate following an impact and explain the results in terms of the nonlinear force law (we measure $\alpha\approx 1.4$). The spatial structure of the forces and the propagation speed, $v_f$, depend on a dimensionless parameter, $M'=t_cv_0/d$, where $v_0$ is the intruder speed at impact, $d$ is the grain diameter, and $t_c$ is a binary collision time between grains with relative speed $v_0$. For $M'\ll 1$, propagating forces are chain-like, and the measured $v_f \propto d/t_c\propto v_b(v_0/v_b)^\frac{\alpha-1}{\alpha+1}$, where $v_b$ is the bulk sound speed. For larger $M'$, the force response has a 2D character, and forces propagate faster than predicted by $d/t_c$ due to collective stiffening of a packing. [Preview Abstract] |
Tuesday, November 25, 2014 8:26AM - 8:39AM |
M1.00003: Forces and flows during high speed impacts on a non-Newtonian suspension Melody Lim, Jonathan Bares, Robert Behringer A suspension made of starch particles dispersed in water displays significant non-Newtonian behavior for high enough particulate concentration. In order to shed light on the possible micro-structural basis of this behavior, we perform collisions on a quasi-2D suspension, using a high speed camera to gain access to the dynamics of the suspension. We suspend small dark particles (charcoal) in the cornstarch suspension. From these, we can carry out particle tracking to determine the velocity field during impact. We observe a shock-like propagation in the cornstarch suspension. Although the dynamics of this shockfront are strongly correlated to the dynamics of the intruder, we find that a simple process of momentum transfer to the suspension is insufficient to account for the force experienced by the impactor. We use boundaries made from a photoelastic material which then registers the arrival of strong forces at the boundaries. By linking the forces observed at the boundaries with the dynamics of the suspension, we assess the role of interactions with the boundaries of the suspension. [Preview Abstract] |
Tuesday, November 25, 2014 8:39AM - 8:52AM |
M1.00004: Head-on collisions of Newtonian and granular jets Jake Ellowitz, Wendy W. Zhang When a wide fluid jet collides head-on with a narrow jet, incompressibility, together with energy and momentum conservation requires that the excess forward momentum flux be transported away from the impact zone by two identical symmetrically-angled ejecta streams. The central impact zone itself remains fixed. Introducing any kind of dissipation breaks time-reversal symmetry, thus allowing the excess forward momentum flux to be partitioned between the ejecta streams and the impact zone. Such a partition would cause the impact zone to drift steadily over time rather than remaining fixed. Motivated by the potential relevance of this mechanism to splash formation and microreactors from impinging jets, we simulate head-on collisions of two Newtonian jets and compare it against collisions of two densely packed granular jets. In both cases, the steady-state solutions display impact zones moving with finite drift speeds. Increasing the dissipation, either by increasing the viscosity of the Newtonian liquid or by increasing the coefficient of friction in the granular system, increases the drift speed. To our surprise, plotting the drift speeds against the total dissipation rates collapses results for Newtonian and granular jets. [Preview Abstract] |
Tuesday, November 25, 2014 8:52AM - 9:05AM |
M1.00005: Does the Fluid Matter? Impact Into Wet Granular Materials Kerstin Nordstrom, Dylan Powers, Sam Arrington, Wolfgang Losert We study the impact of a projectile onto a bed of 3 mm grains immersed in a fluid. We vary the viscosity of the fluid, and see how the impact depth vs impact energy scaling changes. We find only an appreciable change when the viscosity is quite large. We also study the trajectory of the intruder for different viscosities and impact energies. We find these trajectories are well-described by a modified version of the Poncelet-type stopping force model. [Preview Abstract] |
Tuesday, November 25, 2014 9:05AM - 9:18AM |
M1.00006: Granular impact cratering by liquid drops: Understanding raindrop imprints through an analogy of asteroid strikes Xiang Cheng, Runchen Zhao, Qianyun Zhang, Hendro Tjugito When a granular material is impacted by a sphere, its surface deforms like a liquid yet it preserves a circular crater like a solid. Although the mechanism of granular impact cratering by solid spheres is well understood, our knowledge on granular impact cratering by liquid drops is still very limited. Using high-speed photography, we investigate liquid-drop impact dynamics on granular media. Surprisingly, we find that granular impact cratering by liquid drops follows the same energy scaling as that of asteroid impact cratering. Inspired by this similarity, we develop a simple model that quantitatively describes the observed crater morphologies. Our study sheds light on the mechanisms governing raindrop impacts on granular surfaces and reveals an interesting analogy between familiar phenomena of raining and catastrophic asteroid strikes. [Preview Abstract] |
Tuesday, November 25, 2014 9:18AM - 9:31AM |
M1.00007: Influence of particle shape on properties of force networks in particulate systems Lou Kondic, Luis Pugnaloni, Manuel Carlevaro, Miroslav Kramar, Konstantin Mischaikow Simulations of particulate systems usually consider circular or spherical particles due to computational simplicity. Realistic particles however are often not circular or spherical, posing an important question: to what degree particles' shape influences mechanical properties of the corresponding systems? To start answering this question, we carry out MD simulations of circular and polygonal frictional particles exposed to tapping and analyze the resulting force networks. In addition to using classical measures, we carry out topological analysis that allows us to describe and quantify structural properties of the considered networks. Perhaps surprisingly, topological analysis allows us to identify the differences between systems that appear undistinguishable based on the classical measures. [Preview Abstract] |
Tuesday, November 25, 2014 9:31AM - 9:44AM |
M1.00008: Force transmitted to a subsurface due to particle-laden liquids Erik Worden, Reza Gheisari, Parisa Mirbod In this study, we investigate force transmission due to a layer of neutrally buoyant suspension on a substrate. By applying a constant force on a solid body and pushing it through the suspension, some indentations were produced. The profile of the indentations and its relation to the size and squeezing speed of the solid body for three different volume fractions was determined. The dependence of the indentation depth on the compression height was examined and the variation of the indentations depth with strain rate was also investigated. Finally, by characterizing the response of the substrate to deformation, the force transmitted through the suspension was examined and compared to the applied force. We also studied the effect of the substrate material, solid body shape and squeezing speed, concentration of suspension, and the onset of plastic deformation. [Preview Abstract] |
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