01361nas a2200157 4500008004100000245011500041210006900156260000800225300001100233490000700244520076300251100002201014700002101036700002201057856012401079 2006 eng d00aFriction of a slider on a granular layer: non-monotonic thickness dependence and effect of boundary conditions0 aFriction of a slider on a granular layer nonmonotonic thickness  cJAN a0103010 v733 a

We investigate the effective friction encountered by a mass sliding on a granular layer as a function of bed thickness and boundary roughness conditions. The observed friction has minima for a small number of layers before it increases and saturates to a value that depends on the roughness of the sliding surface. We use an index-matched interstitial liquid to probe the internal motion of the grains with fluorescence imaging in a regime where the liquid has no significant effect on the measured friction. The shear profiles obtained as a function of depth show a decrease in slip near the sliding surface as the layer thickness is increased. We propose that the friction depends on the degree of grain confinement relative to the sliding surfaces.

1 aSiavoshi, Saloome1 aOrpe, Ashish, V.1 aKudrollim, Arshad uhttp://library.ncl.res.in/content/friction-slider-granular-layer-non-monotonic-thickness-dependence-and-effect-boundary01861nas a2200181 4500008004100000022001400041245010200055210006900157260010300226300001000329490000700339520113400346100002101480700001601501700001601517700002101533856012501554 2008 eng d a0295-507500aFast decay of the velocity autocorrelation function in dense shear flow of inelastic hard spheres0 aFast decay of the velocity autocorrelation function in dense she a17, AVE DU HOGGAR, PA COURTABOEUF, BP 112, F-91944 LES ULIS CEDEX A, FRANCEbEDP SCIENCES S AcDEC a640030 v843 a

We find in complementary experiments and event-driven simulations of sheared inelastic hard spheres that the velocity autocorrelation function psi(t) decays much faster than t(-3/2) obtained for a fluid of elastic spheres at equilibrium. Particle displacements are measured in experiments inside a gravity-driven flow sheared by a rough wall. The average packing fraction obtained in the experiments is 0.59, and the packing fraction in the simulations is varied between 0.5 and 0.59. The motion is observed to be diffusive over long times except in experiments where there is layering of particles parallel to boundaries, and diffusion is inhibited between layers. Regardless, a rapid decay of psi(t) is observed, indicating that this is a feature of the sheared dissipative fluid, and is independent of the details of the relative particle arrangements. An important implication of our study is that the non-analytic contribution to the shear stress may not be present in a sheared inelastic fluid, leading to a wider range of applicability of kinetic theory approaches to dense granular matter. Copyright (C) EPLA, 2008

1 aOrpe, Ashish, V.1 aKumaran, V.1 aReddy, Anki1 aKudrolli, Arshad uhttp://library.ncl.res.in/content/fast-decay-velocity-autocorrelation-function-dense-shear-flow-inelastic-hard-spheres-001965nas a2200181 4500008004100000022001400041245005100055210005000106260010300156300001000259490000700269520135100276100001801627700002101645700001701666700001801683856008201701 2012 eng d a0295-507500aFlow-induced channelization in a porous medium0 aFlowinduced channelization in a porous medium a6 RUE DES FRERES LUMIERE, MULHOUSE, 68200, FRANCEbEPL ASSOCIATION, EUROPEAN PHYSICAL SOCIETYcJUN a580030 v983 a

Flow through a saturated, granular, porous medium can lead to internal erosion, preferential flow enhancement, and the formation of channels within the bulk of the medium. We examine this phenomenon using a combination of experimental observations, continuum theory and numerical simulations in a minimal setting. Our experiments are carried out by forcing water through a Hele-Shaw cell packed with bidisperse grains. When the local flow-induced stress exceeds a critical threshold, the smaller grains are dislodged and transported. This changes the porosity of the medium, thence, the local hydraulic conductivity, and leads to the development of erosional channels. Erosion is ultimately arrested due to the drop in the mean pressure gradient, while most of the flow occurs through the channels. We describe this using a minimal multiphase description of erosion where the volume fraction of the fluid, mobile, and immobile, grains change in space and time. Numerical solutions of the resulting initial boundary value problem yield results for the dynamics and morphology that are in qualitative agreement with our experiments. In addition to providing a basis for channelization in porous media, our study highlights how heterogeneity in porous media may arise from flow as a function of the erosion threshold. Copyright (C) EPLA, 2012

1 aMahadevan, A.1 aOrpe, Ashish, V.1 aKudrolli, A.1 aMahadevan, L. uhttp://library.ncl.res.in/content/flow-induced-channelization-porous-medium-001583nas a2200181 4500008004100000022001400041245008500055210006900140260007900209300001100288490000700299520091600306100002001222700001601242700001801258700002101276856010401297 2014 eng d a1539-375500aFlow of granular matter in a silo with multiple exit orifices: jamming to mixing0 aFlow of granular matter in a silo with multiple exit orifices ja aONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USAbAMER PHYSICAL SOCcDEC a0622060 v903 a

We investigate the mixing characteristics of dry granular material while draining down a silo with multiple exit orifices. The mixing in the silo, which otherwise consists of noninteracting stagnant and flowing regions, is observed to improve significantly when the flow through specific orifices is stopped intermittently. This momentary stoppage of flow through the orifice is either controlled manually or is chosen by the system itself when the orifice width is small enough to cause spontaneous jamming and unjamming. We observe that the overall mixing behavior shows a systematic dependence on the frequency of closing and opening of specific orifices. In particular, the silo configuration employing random jamming and unjamming of any of the orifices shows early evidence of chaotic mixing. When operated in a multipass mode, the system exhibits a practical and efficient way of mixing particles.

1 aKamath, Sandesh1 aKunte, Amit1 aDoshi, Pankaj1 aOrpe, Ashish, V. uhttp://library.ncl.res.in/content/flow-granular-matter-silo-multiple-exit-orifices-jamming-mixing-001699nas a2200181 4500008004100000022001400041245007600055210006900131260008700200300001100287490000700298520102400305100002301329700002601352700001801378700002101396856010001417 2016 eng d a1070-663100aFingering instability of a suspension film spreading on a spinning disk0 aFingering instability of a suspension film spreading on a spinni a1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USAbAMER INST PHYSICScJUN a0633030 v283 a

The spreading of a thin film of suspension on a spinning disk and the accompanying contact line instability is studied through flow visualization experiments. The critical radius for the onset of instability shows an increase with increase in the particle fraction (phi(p)) before decreasing slightly at the highest value of phi(p) studied, while the instability wavelength (lambda) exhibits a non-monotonic dependence. The value of lambda is close to that for a partially wetting liquid at lower phi(p), it decreases with increasing phi(p) to a minimum before increasing again at largest phi(p). The non-monotonic trends observed for lambda are discussed in light of the linear stability analysis of thin film equations derived for suspensions by Cook et al. [''Linear stability of particle-laden thin films,'' Eur. Phys. J.: Spec. Top. 166, 77 (2009)] and Balmforth et al. [''Surface tension driven fingering of a viscoplastic film,'' J. Non Newtonian Fluid Mech. 142, 143 (2007)]. Published by AIP Publishing.

1 aKulkarni, Mayuresh1 aSahoo, Subhadarshinee1 aDoshi, Pankaj1 aOrpe, Ashish, V. uhttp://library.ncl.res.in/content/fingering-instability-suspension-film-spreading-spinning-disk01882nas a2200157 4500008004100000022001400041245008800055210006900143260000900212300001100221490000800232520133300240100002101573700001801594856011201612 2019 eng d a2470-004500aFriction-mediated flow and jamming in a two-dimensional silo with two exit orifices0 aFrictionmediated flow and jamming in a twodimensional silo with  cJUL  a0129010 v1003 a

We show that the interparticle friction coefficient significantly influences the flow and jamming behavior of granular materials exiting through the orifice of a two-dimensional silo in the presence of another orifice located in its vicinity. The fluctuations emanating from a continuous flow through a larger orifice results in an intermittent flow through the smaller orifice consisting of sequential jamming and flowing events. The mean time duration of jammed and flow events, respectively, increase and decrease monotonically with increasing interparticle friction coefficient. The frequency of unjamming instances (n(u)), however, shows a nonmonotonic behavior comprising an increase followed by a decrease with increasing friction coefficient. The decrease on either side of the maximum, then, represents a system moving progressively towards a permanently jammed or a permanently flowing state. The overall behavior shows a systematic dependence on the interorifice distance, which determines the strength of the fluctuations reaching the smaller orifice leading to unjamming instances. The probability distributions of jamming and flowing times are nearly similar for different combinations of friction coefficients and interorifice distances studied and, respectively, exhibit exponential and power-law tails.

1 aOrpe, Ashish, V.1 aDoshi, Pankaj uhttp://library.ncl.res.in/content/friction-mediated-flow-and-jamming-two-dimensional-silo-two-exit-orifices01437nas a2200157 4500008004100000022001400041245006700055210006700122260000800189490000700197520092500204100002301129700001801152700002101170856008801191 2024 eng d a1070-663100aFlow and clogging behavior of a mixture of particles in a silo0 aFlow and clogging behavior of a mixture of particles in a silo cMAY0 v363 a

We investigated the clogging behavior observed during the flow of aspherical particles from a silo in the presence of spherical particles of different sizes and proportions using flow visualization experiments and discrete element method simulations. The size of the avalanche, essentially the tendency of clogging, exhibits non-monotonic dependence on the spherical particle volume fraction. For small enough content of spherical particles, the clogging tendency intensifies, whereas it reduces rapidly for high enough spherical particle fractions, with a minimum in between. The non-monotonic behavior is observed to persist over for different spherical particle sizes. The overall behavior is shown to arise due to competing effects between the localized total particle fraction influencing avalanche strength and mean size of the particles exiting the silo, influencing the probability of arch formation.

1 aBhure, Sukhada, C.1 aDoshi, Pankaj1 aOrpe, Ashish, V. uhttp://library.ncl.res.in/content/flow-and-clogging-behavior-mixture-particles-silo