Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session C29: Mesoscale Structure in Particulate-based SystemsInvited
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Sponsoring Units: GSNP GSOFT Chair: Lou Kondic, New Jersey Institute of Techology Room: 292 |
Monday, March 13, 2017 2:30PM - 3:06PM |
C29.00001: Rheology of active suspensions: from individual to collective effort Invited Speaker: Eric Clement Future developments in bio-technologies involving micro-organisms, demand a fundamental understanding of the emerging hydrodynamics properties of suspensions laden with swimming bacteria. We are currently interested in the fluid properties modified by the presence of active microscopic swimmers such as E.coli. In such a context, due to individual or collective organization, one may observe properties significantly at odd with their classical “passive” counterpart. One may quote for example activated Brownian motion [1], anomalous transport in confined flows [2] or non-standard rheological response [3]. In order to provide a consistent physical and mechanical picture from the microscopic swimming properties, up to the macroscopic level, we developed various experimental tools microfluidic channels or specific rheological devices) to monitor either the individual 3D Lagrangian trajectories or the outcome of collective effects. We will discuss in particular, recent results probing the role of the swimming organization on the effective suspension rheology. [1] Mino et al. Phys.Rev.Lett. 106, 048102 (2011). [2] Altshuler et al., Soft-Matter, 9 , 1864 (2013) ; Figueroa-Morales et al. Soft Matter 11, 6284 (2015). [3] Lopez et al.,Phys. Rev. Lett. 115, 028301 (2015). [Preview Abstract] |
Monday, March 13, 2017 3:06PM - 3:42PM |
C29.00002: Stress correlations in the transition region of discontinuously thickening suspension flows Invited Speaker: Jeffrey Morris In concentrated suspensions of particles in liquids, the apparent viscosity and the normal stresses are often found to undergo an abrupt transition from a low-viscosity to a high-viscosity state. This behavior happens in a range of materials, for example dispersions of sub-micron spheres in organic liquids to 20-micron diameter corn starch particles in water. While the mechanism may differ for different materials, one scenario which is able to explain this type of behavior is that as the shear stress increases, a stabilizing force which maintains liquid-filled gaps between the particles transitions to one in which contact occurs and frictional interactions between the particles plays a role. \par This lubricated-frictional transition is explored using an established simulation approach for spherical particles in viscous liquid [1,2]. The behavior will first be shown to exhibit a shear rate- or stress-induced transition which has features of a classical phase transition. The point equivalent to a critical point is thus the point at which the variation of the shear stress (and typically also the mean particle normal stress) with respect to the shear rate becomes infinite. This point is associated with a pairing of solid fraction and friction coefficient , $\phi$ and $\mu$ respectively. The temporal fluctuations and spatial correlations of the mixture stress are examined and shown to exhibit a striking change as this transition is crossed. \par 1. R. Mari, R. Seto, J. F. Morris & M. M. Denn 2014 “Shear thickening, frictionless and frictional rheologies in non-Brownian suspensions” {\emph J. Rheol.} {\bf 58}, 1693. \par 2. R. Mari, R. Seto, J. F. Morris & M. M. Denn 2015 Discontinuous shear thickening in Brownian suspensions by dynamic simulation. {\emph Proc. National Acad. Sci.} {\bf 112}, 15326. [Preview Abstract] |
Monday, March 13, 2017 3:42PM - 4:18PM |
C29.00003: Clogging arches in grains, colloids, and pedestrians flowing through constrictions Invited Speaker: Iker Zuriguel When a group of particles pass through a narrow orifice, the flow might become intermittent due to the development of clogs that obstruct the constriction. This effect has been observed in many different fields such as mining transport, microbial growing \cite{microbialclogging}, crowd dynamics, colloids, granular and active matter \cite{Zuriguel:2014}. In this work we introduce a general framework in which research in some of such scenarios can be encompassed. In particular, we analyze the statistical properties of the bottleneck flow in different experiments and simulations: granular media within vibrated silos, colloids, a flock of sheep and pedestrian evacuations. We reveal a common phenomenology that allows us to rigorously define a transition to a clogged state. Using this definition we explore the main variables involved, which are then grouped into three generic parameters. In addition, we will present results of the geometrical characteristics that the clogging arches have which are related with their stability against perturbations \cite{LozanoPRLarcos}. We experimentally analyse the temporal evolution of the arches evidencing important differences among the structures that are easily destroyed and those that seem to resist forever (longer than the temporal window employed in our measurements). \begin{thebibliography}{26} \bibitem{microbialclogging} M. Delarue et al., Nature Physics \textbf{12}, 762 (2016). \bibitem{Zuriguel:2014} I. Zuriguel et al., Scientific Reports \textbf{4}, 7324 (2014). \bibitem{LozanoPRLarcos} C. Lozano et al, Phys. Rev. Lett. \textbf{109}, 068001 (2012). \end{thebibliography} [Preview Abstract] |
Monday, March 13, 2017 4:18PM - 4:54PM |
C29.00004: Evolution of network architecture in a granular material under compression Invited Speaker: Danielle Bassett As a granular material is compressed, the particles and forces within the system arrange to form complex and heterogeneous collective structures. However, capturing and characterizing the dynamic nature of the intrinsic inhomogeneity and mesoscale architecture of granular systems can be challenging. Here, we utilize multilayer networks as a framework for directly quantifying the evolution of mesoscale architecture in a compressed granular system. We examine a quasi-two-dimensional aggregate of photoelastic disks, subject to biaxial compressions through a series of small, quasistatic steps. Treating particles as network nodes and inter-particle forces as network edges, we construct a multilayer network for the system by linking together the series of static force networks that exist at each strain step. We then extract the inherent mesoscale structure from the system by using a generalization of community detection methods to multilayer networks, and we define quantitative measures to characterize the reconfiguration and evolution of this structure throughout the compression process. To test the sensitivity of the network model to particle properties, we examine whether the method can distinguish a subsystem of low-friction particles within a bath of higher-friction particles. We find that this can be done by considering the network of tangential forces, and that the community structure is better able to separate the subsystem than consideration of the local inter-particle forces alone. The results discussed throughout this study suggest that these novel network science techniques may provide a direct way to compare and classify data from systems under different external conditions or with different physical makeup. [Preview Abstract] |
Monday, March 13, 2017 4:54PM - 5:30PM |
C29.00005: Characterizing Granular Networks Using Topological Metrics Invited Speaker: Joshua Dijksman We consider a granular system as it undergoes shear jamming. Using measures ranging from microscopic, through mesoscopic to system-wide characteristics, we observe that mesoscopic force networks properties provide a key link between micro and macro scales. To show the importance of mesoscopic length scales, we carry out both physical experiments and simulations that carefully reproduce the experimental conditions. The acquired data are directly compared across the different spatial scales. We find that the conventional measures, including stresses and contact numbers are similar between experiments and simulations. In particular, the various measures presented here depend in a universal manner on the fraction of non-rattler particles, $f_{NR}$. However, force networks exhibit high sensitivity to small differences between experiments and simulations. These differences are clearly captured by topological measures. We show that topological methods are needed for meaningful comparison between experiments and simulations. [Preview Abstract] |
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