Comment letters to the National Commission on Commission on Fraudulent Financial Reporting, 1987 (Treadway Commission) Vol. 2

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Effect of particle shape on domino wave propagation: a perspective from 3D, anisotropic discrete element simulations

A fundamental understanding of the underlying physics of granular systems is not only of academic interest, but is also relevant for industrial applications. One specific aspect that is currently only poorly understood is the effect of particle shape on the dynamics of such systems. In this work the effect of particle shape on domino wave propagation was studied using 3D, anisotropic discrete element simulations. The dominoes were modelled using the three-dimensional super-quadric equation and very good agreement between the intrinsic collision speeds predicted by the simulations and the corresponding experimental data was observed. Furthermore, the influence of particle blockiness on the collision dynamics of dominoes was investigated numerically using particle shapes ranging from ellipsoids to almost cuboid particles. It was found that the intrinsic collision speed increased with increasing particle blockiness. It was also shown that a higher initial contact point favours the transmission of kinetic energy in the direction of the wave propagation, leading to a higher intrinsic collision speed for dominoes of higher blockiness.ISSN:1434-5021ISSN:1434-763

The parameters governing the coefficient of dispersion of cubes in rotating cylinders

ISSN:1434-5021ISSN:1434-763

Comparison between finite volume and lattice-Boltzmann method simulations of gas-fluidised beds: bed expansion and particle-fluid interaction force

ISSN:2196-4378ISSN:2196-438

Experimental investigation of axial dispersion in a horizontal rotating cylinder

This work reports experimental measurements of the dispersion of particles during rotation in a horizontal cylinder. The axial dispersion of a pulse of approximately monodisperse black glass ballotini into a bed of clear glass ballotini of the same size is analysed. This is done using a sectioning technique, where the concentration is determined throughout the cylinder for a given rotation time and speed. The concentration profile is fitted to an appropriate solution of Fick’s second law to determine the dispersion coefficient. The dispersion coefficient is compared for various drum rotation rates and glass ballotini sizes. The cylinder was filled to 35 % by volume and rotated at a range of speeds between 5 and 20 rpm. The particle sizes vary from 1.14 to 3.15 mm. The dispersion coefficient was found to be dependent on both particle size and rotation speed. As the rotation speed,ISSN:1434-5021ISSN:1434-763

Modelling axial dispersion of granular material in inclined rotating cylinders with bulk flow

The axial dispersion of approximately monosized particles in rolling mode in rotating cylinders with bulk flow is examined using a Monte Carlo model and discrete element method (DEM) simulations. The Monte Carlo model predicts that the mean square displacement relative to the mean axial displacement of the bed undergoes oscillations in time. The nature of these oscillations depends on the fill level of the cylinder and the extent of particle mixing during avalanches. When the cylinder is half full the Monte Carlo model predicts undamped oscillations, whereas a filling fraction of 0.26 produces oscillations whose amplitude decreases with time. If mixing during avalanches is assumed to be perfect then the oscillations occur about a linear increase with time. In contrast, if it is assumed that the particles do not mix during avalanching, the oscillations occur about an increase with time which has a gradient which increases with time. There is good qualitative agreement between the Monte Carlo model with perfect mixing and the DEM when the filling fraction is 0.26. For a filling fraction of 0.5 the DEM data show oscillations about a faster than linear increase with time.ISSN:1434-5021ISSN:1434-763

Ordering and stress transmission in packings of straight and curved spherocylinders

In this work we apply the discrete element method (DEM) to model packings of spherocylinders. The so-called composite spheres method was used to construct particles of different aspect ratio, surface shape and curvature. Using the DEM we probe in detail the effect of particle curvature and surface shape on packing morphology and stress transmission. We find that particle shape has a remarkable influence on both the packing morphology (quantified via the solid fraction, particle orientation distribution and radial distribution function) and stress transmission. Specifically, elongated particles have a high preference for horizontal alignment, whereas an increasing particle curvature leads to a more continuous (i.e. less discrete) particle orientation distribution. Generally, we observe that rough and curved particles have a stronger tendency for interlocking (in particular for small particle aspect ratios, i.e. AR = 2 and 3) leading to the formation of dense packing structures. In addition packings of rough and curved particles of small aspect ratios favor stress transmission in the gravitational direction, thus, limiting stress saturation with depth.ISSN:1434-5021ISSN:1434-763