Discrete element modeling of particulate solids in silos

In this study, a series of discrete element simulations were performed to elucidate the mechanical behavior of particulate materials and their effect on silo wall loads during filling and discharge. The wall pressures were evaluated using a moving average method and the effect of the averaging length of 5 to 15 times the mean particle size was explored. The evaluated wall pressure distribution was quite well represented by a least squares fit to the Janssen theory, which also yielded interesting measures of macroscopic performance. Previous simulations have predicted that shear localization may occur during the discharging of a silo containing monosized particles. This phenomenon is strongly affected by three phenomena: heterogeneity, intensive rotation and dilatancy. The occurrence and evolution of shear ruptures are affected by the properties assumed for the individual particles. However, the orientation angles of the shear rupture planes have been found to be fairly constant within a narrow range. A simple analysis to estimate the dynamic over-pressure on silo walls arising from shear rupture planes is proposed. The pressures so derived are of the right order of magnitude to match experimental observations, and can explain non-symmetric features of wall pressures, together with spatial and temporal fluctuations.