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This paper investigates the explosively driven dynamics of dry and wet sand. Contrary to popular belief, wet sand under high strain rate loadings (10~4s~(-1)) is observed to have reduced resistance against flow compared to the dry...
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This paper investigates the explosively driven dynamics of dry and wet sand. Contrary to popular belief, wet sand under high strain rate loadings (10~4s~(-1)) is observed to have reduced resistance against flow compared to the dry sand, which is supported by a noticeably enhanced expansion before the breakup followed by an increased number of fragments. Even a small amount of interstitial oil (3.2wt.%) suffices to substantially reduce the size of fragments whose average mass only amounts to 60% of the mass of the dry sand fragments. To predict the instability onset of the expanding sand shell, a kinetic instability model is proposed based on an instability criterion involving the opposing forces of stabilizing inertial pressures and destabilizing viscous resistance. The interstitial oil leads to a smaller viscous resistance of wet sand by the lubrication effect as well as lessening the degree of shock compaction. The dominance of viscous resistance thus commences later for the wet sand shell until a smaller thickness allows the inertial forces to be overtaken. Moreover, multi-shear localizations rather than interface instability are identified as the dominant mechanism for the instability onset of the expanding sand shells. Graphical abstract: [Figure not available: see fulltext.]
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Abstract. States of self stress (SSS) are assignments of forces on the edges of a network that satisfy mechanical equilibrium in the absence of external forces. In this work we show that a particular class of quasilocalized SSS in...
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Abstract. States of self stress (SSS) are assignments of forces on the edges of a network that satisfy mechanical equilibrium in the absence of external forces. In this work we show that a particular class of quasilocalized SSS in packing-derived networks, first introduced by D.M. Sussman, C.P. Goodrich, A.J. Liu (Soft Matter 12 , 3982 (2016)), are characterized by a decay length that diverges as $ 1/\sqrt{z_c-z}$ 1 / z c - z , where $ z$ z is the mean connectivity of the network, and $ z_c \equiv 4$ z c ≡ 4 is the Maxwell threshold in two dimensions, at odds with previous claims. Our results verify the previously proposed analogy between quasilocalized SSS and the mechanical response to a local dipolar force in random networks of relaxed Hookean springs. We show that the normalization factor that distinguishes between quasilocalized SSS and the response to a local dipole constitutes a measure of the mechanical coupling of the forced spring to the elastic network in which it is embedded. We further demonstrate that the lengthscale that characterizes quasilocalized SSS does not depend on its associated degree of mechanical coupling, but instead only on the network connectivity. Graphical abstract.
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We investigate experimentally the runout resulting from the collapse of a granular column containing two particle species that differ in size only. The experimental configuration is strictly two-dimensional (only one particle per ...
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We investigate experimentally the runout resulting from the collapse of a granular column containing two particle species that differ in size only. The experimental configuration is strictly two-dimensional (only one particle per width of the experimental tank) and we explore both the role of the initial arrangement and proportion of the two particle sizes in the column, using high-speed videography, and by determining the centres of mass of the big and small particles in the initial column and the final deposit. The duration of the experiment is sufficiently short that large-scale segregation does not occur, however, we find a clear dependence of runout on both initial mixture arrangement and proportion for all conditions. We investigated this observation through detailed analysis of the flow front motion, and identify a characteristic "stopping" phase when dissipation dominates, and we apply a shallow layer model at the flow front to show how the initial mixture arrangement and proportion influence the effective coefficient of friction during emplacement. We find that a bidispersed mixture can induce a larger friction on emplacement than a monodispersed mixture, and the highest coefficient of friction was found for a well-mixed initial arrangement of particles at the proportion that shows maximum horizontal spreading of the flow. These observations suggest that downwards percolation of fine particles takes place at the front of the collapsing column, and so localised size segregation processes at the flow front can control flow mobility. This effect is likely to be important in controlling the mobility of large geophysical flows that occur on finite time scales, and whose deposits typically show granular segregation at the front and edges but not throughout the entire deposit.
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Abstract. The waves in a one-dimensional (1-D) bead chain produced by a constant velocity impact in a short period are studied numerically in the present paper. It seems that in some cases, the waves look like a shock wave, while ...
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Abstract. The waves in a one-dimensional (1-D) bead chain produced by a constant velocity impact in a short period are studied numerically in the present paper. It seems that in some cases, the waves look like a shock wave, while in other cases they may be composed of several solitary waves or some oscillations. These characteristics depend on both the bead parameters and the impact parameters, such as the plasticity of the bead material, the piston velocity and the impact duration. It is found that the shock structure appears if the duration of the impact is longer, while it will evolve into several solitary waves if the duration of the impact is small enough. This indicates that the bead velocity attenuates with power function. The strength of the attenuation depends on the plasticity, the piston velocity and the bead radius. Graphical abstract.
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The segregation of binary mixtures in a filled rotating double-walled drum is explored by simulations. Based on the characteristics of self-gravity and the centrifugal force, we argue that both percolation and buoyancy effects dom...
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The segregation of binary mixtures in a filled rotating double-walled drum is explored by simulations. Based on the characteristics of self-gravity and the centrifugal force, we argue that both percolation and buoyancy effects dominate the segregation process. The simulational results show that up to long enough times the segregation state is controlled by the rotational speed, the particle radius and density. At low rotational speeds, the smaller and heavier particles tend to accumulate towards the inner drum wall and the bigger and lighter ones towards the outer drum wall, while the segregation pattern reverses completely at higher rotational speeds. Two typical phase diagrams in the space of the density and radius ratio of bigger particles to smaller particles further confirm the predictions.
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Gravitational billiards composed of a viscoelastic frictional disk bouncing on a vibrating wedge have been studied previously, but only from the point of view of their translational behavior. In this work, the average rotational v...
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Gravitational billiards composed of a viscoelastic frictional disk bouncing on a vibrating wedge have been studied previously, but only from the point of view of their translational behavior. In this work, the average rotational velocity of the disk is studied under various circumstances. First, an experimental realization is briefly presented, which shows sustained rotation when the wedge is tilted. Next, this phenomenon is scrutinized in close detail using a precise numerical implementation of frictional forces. We show that the bouncing disk acquires a spontaneous rotational velocity whenever the wedge angle is not bisected by the direction of gravity. Our molecular dynamics ( MD) results are well reproduced by event-driven ( ED) simulations. When the wedge aperture angle theta(W) > pi/2, the average tangential velocity R (omega) over bar of the disk scales with the typical wedge vibration velocity v(b), and is in general a nonmonotonic function of the overall tilt angle theta(T) of the wedge. The present work focuses on wedges with theta(W) = 2 pi/3, which are relevant for the problem of spontaneous rotation in vibrated disk packings. This study makes part of the PhD Thesis of G. G. Peraza-Mues.
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We study the front shape of avalanches produced in a rotating two-dimensional drum partially filled with small glass beads. We focus our work on the study of the length and shape of granular fronts, in particular how they do scale...
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We study the front shape of avalanches produced in a rotating two-dimensional drum partially filled with small glass beads. We focus our work on the study of the length and shape of granular fronts, in particular how they do scale in terms of the physical parameters involved. A single scaling law for the length is found. This scaling law is also relevant for the behavior of the full shape of the fronts. More than 300 different fronts shape, for different values of the parameters collapse into an universal curve. (c) 2005 Elsevier B.V. All rights reserved.
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Diffusional mixing of a granular system differs from that of fluid systems in many respects, being the most important, the lack of particulate motion equivalent to molecular diffusion; i.e., there is no relative movement of partic...
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Diffusional mixing of a granular system differs from that of fluid systems in many respects, being the most important, the lack of particulate motion equivalent to molecular diffusion; i.e., there is no relative movement of particles without an energy input. If we can design a mixer that gives the grains the nec- Essary energy to flow and, at he same time, changes ran- Domly their velocities, we will, in principle, simulate the diffusive movements of molecules in a liquid or gas.
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Active fluids exhibit properties reminiscent of equilibrium systems when their degrees of freedom are statistically decoupled. A theory for the fluctuating hydrodynamics of these fluids offers a probe of their anomalous transport ...
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Active fluids exhibit properties reminiscent of equilibrium systems when their degrees of freedom are statistically decoupled. A theory for the fluctuating hydrodynamics of these fluids offers a probe of their anomalous transport coefficients. Active materials are characterized by continuous injection of energy at the microscopic level and typically cannot be adequately described by equilibrium thermodynamics. Here we study a class of active fluids in which equilibrium-like properties emerge when fluctuating and activated degrees of freedom are statistically decoupled, such that their mutual information is negligible. We analyse three paradigmatic systems: chiral active fluids composed of spinning frictional particles that are free to translate, oscillating granular gases and active Brownian rollers. In all of these systems, a single effective temperature generated by activity parameterizes both the equation of state and the emergent Boltzmann statistics. The same effective temperature, renormalized by velocity correlations, relates viscosities to steady-state stress fluctuations via a Green-Kubo relation. To rationalize these observations, we develop a theory for the fluctuating hydrodynamics of these non-equilibrium fluids and validate it through large-scale molecular dynamics simulations. Our work sheds light on the microscopic origin of odd viscosities and stress fluctuations characteristic of parity-violating fluids, in which mirror symmetry and detailed balance are broken.
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The science of granular matter has expanded from an activity for specialised engineering applications to a fundamental field in its own right. This has been accompanied by an explosion of research and literature, which cannot be r...
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The science of granular matter has expanded from an activity for specialised engineering applications to a fundamental field in its own right. This has been accompanied by an explosion of research and literature, which cannot be reviewed in one paper. A key to progress in this field is the formulation of a statistical mechanical formalism that could help develop equations of state and constitutive relations. This paper aims at reviewing some milestones in this direction. An essential basic step toward the development of any static and quasi-static theory of granular matter is a systematic and useful method to quantify the grain-scale structure and we start with a review of such a method. We then review and discuss the ongoing attempt to construct a statistical mechanical theory of granular systems. Along the way, we will clarify a number of misconceptions in the field, as well as highlight several outstanding problems.
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