scholarly journals Self-diffusion scalings in dense granular flows

Soft Matter ◽  
2021 ◽  
Author(s):  
Riccardo Artoni ◽  
Michele Larcher ◽  
James T. Jenkins ◽  
Patrick Richard
Keyword(s):  
Shear Rate ◽  
Solid Fraction ◽  
Granular Flows ◽  
The Self ◽  
Granular Temperature ◽  
Restitution Coefficient ◽  
Self Diffusion ◽  
Diffusivity Tensor ◽  
Dense Granular Flows

The self-diffusivity tensor in homogeneously sheared dense granular flows is anisotropic. We show how its components depend on solid fraction, restitution coefficient, shear rate, and granular temperature.

Long-range wall perturbations in dense granular flows

2014 ◽  
Vol 764 ◽  
pp. 171-192 ◽  
Author(s):  
Pierre G. Rognon ◽  
Thomas Miller ◽  
Bloen Metzger ◽  
Itai Einav
Keyword(s):  
Shear Rate ◽  
Power Law ◽  
Eddy Viscosity ◽  
Granular Flows ◽  
Length Scale ◽  
Local Models ◽  
Plane Shear ◽  
Eddy Viscosity Model ◽  
Non Local ◽  
Dense Granular Flows

AbstractWe explore how the rheology of dense granular flows is affected by the presence of sidewalls. The study is based on discrete element method simulations of plane-shear flows between two rough walls, prescribing both the normal stress and the shear rate. Results confirm previous observations for different systems: large layers near the walls develop where the local viscosity is not constant, but decreases when approaching the walls. The size of these layers can reach several dozen grain diameters, and is found to increase when the flow decelerates, as a power law of the inertial number. Two non-local models are found to adequately explain such features, namely the kinetic elasto-plastic fluidity (KEP) model and the eddy viscosity model (EV). The analysis of the internal kinematics further shows that the vorticity and its associated length scale may be a key component of these non-local behaviours.

scholarly journals Shear-induced diffusion: the role of granular clusters

2021 ◽  
Vol 249 ◽  
pp. 03035
Author(s):  
Matthew Macaulay ◽  
Pierre Rognon
Keyword(s):  
Granular Flows ◽  
Plane Shear ◽  
Self Diffusion ◽  
Physical Mechanisms ◽  
Dem Simulations ◽  
Starting Point ◽  
Correlated Motion ◽  
Contact Adhesion ◽  
Dense Granular Flows

This paper is concerned with the physical mechanisms controlling shear-induced diffusion in dense granular flows. The starting point is that of the granular random walk occurring in diluted granular flows, which underpins Bagnold’s scaling relating the coefficient of self-diffusion to the grain size and shear rate. By means of DEM simulations of plane shear flows, we measure some deviations from this scaling in dense granular flows with and without contact adhesion. We propose to relate these deviations to the development of correlated motion of grains in these flows, which impacts the magnitude of grain velocity fluctuations and their time persistence.

Shear-induced diffusion in cohesive granular flows: effect of enduring clusters

2018 ◽  
Vol 858 ◽  
Author(s):  
Matthew Macaulay ◽  
Pierre Rognon
Keyword(s):  
Shear Flows ◽  
Granular Flows ◽  
Time Correlation ◽  
Plane Shear ◽  
Velocity Fluctuations ◽  
Self Diffusion ◽  
Cohesive Forces ◽  
Dense Granular Flows

We investigate the effect of intergranular cohesive forces on the properties of self-diffusion in dense granular flows. The study is based on a series of simulated plane shear flows at different inertial and cohesion numbers, in which transverse diffusivities are measured. Results evidence an increase in diffusivity by up to two orders of magnitude when introducing cohesion. This strong effect is analysed using the Green–Kubo framework, expressing the diffusivity in terms of instantaneous grain velocity fluctuations and their time correlation. This analysis shows that cohesion, by forming enduring clusters in the flow, enhances the velocity fluctuations and their time persistence, which both contribute to enhancing grain mixing and self-diffusion.

scholarly journals Influence of granular temperature and grain rotation on the wall friction coefficient in confined shear granular flows

2021 ◽  
Vol 249 ◽  
pp. 03026
Author(s):  
Cheng-Chuan Lin ◽  
Riccardo Artoni ◽  
Fu-Ling Yang ◽  
Patrick Richard
Keyword(s):  
Friction Coefficient ◽  
Granular Matter ◽  
Scaling Law ◽  
Three Dimensional ◽  
Granular Flows ◽  
Force Sensor ◽  
Wall Friction ◽  
Granular Temperature ◽  
Research Perspective ◽  
Dense Granular Flows

A depth-weakening wall friction coefficient, µw, has been reported from three-dimensional numerical simulations of steady and transient dense granular flows. To understand the degradation mechanisms, a scaling law for µw/ f and χ has been proposed where f is the intrinsic particle-wall friction and χ is the ratio of slip velocity to square root of granular temperature (Artoni & Richard, Phys. Rev. Lett., vol. 115 (15), 2015, 158001). Independently, a friction degradation model has been derived which describes a monotonically diminishing friction depends on a ratio of grain angular and slip velocities, Ω (Yang & Huang, Granular Matter, vol. 18 (4), 2016, 77). In search of experimental evidence for how these two parameters degrade the µw, an annular shear cell experiment was performed to estimate the bulk granular temperature, angular and slip velocities at sidewall through image-processing. Meanwhile, µw was measured by a force sensor to confirm the weakening towards the creep zone. The measured µw/ f − χ and µw/ f − Ω were both well-fitted to the corresponding models showing that both granular temperature and angular velocity are significant mechanisms to degrade the µw which broadens the research perspective on modeling the boundary condition of dense granular flows.

scholarly journals Self-Diffusion Coefficients, Aggregation Numbers and the Range of Existence of Spherical Micelles of Oxyethylated Alkylphenols

2021 ◽  
Author(s):  
Victor P. Arkhipov ◽  
Natalia A. Kuzina ◽  
Andrei Filippov
Keyword(s):  
Aqueous Solutions ◽  
Diffusion Coefficients ◽  
The Self ◽  
Self Diffusion ◽  
Aggregation Numbers ◽  
Temperature Ranges ◽  
Spherical Micelles ◽  
Limiting Values

AbstractAggregation numbers were calculated based on measurements of the self-diffusion coefficients, the effective hydrodynamic radii of micelles and aggregates of oxyethylated alkylphenols in aqueous solutions. On the assumption that the radii of spherical micelles are equal to the lengths of fully extended neonol molecules, the limiting values of aggregation numbers corresponding to spherically shaped neonol micelles were calculated. The concentration and temperature ranges under which spherical micelles of neonols are formed were determined.

Direct determination of the self-diffusion mechanism in bccβ-titanium

1989 ◽  
Vol 39 (8) ◽  
pp. 5025-5034 ◽  
Author(s):  
G. Vogl ◽  
W. Petry ◽  
Th. Flottmann ◽  
A. Heiming
Keyword(s):  
Diffusion Mechanism ◽  
Direct Determination ◽  
The Self ◽  
Self Diffusion
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