Analysis of silo asymmetry normal pressures due to eccentric discharge using DEM simulation

The eccentric discharge of bulk solids from a silo can lead to asymmetry in the normal pressure distribution around the silo walls. The non-uniformity and eccentricities of the wall loads, which would cause bending stresses in the circumferential direction at various levels, can have serious structural consequences. Understanding how the wall loads are affected by eccentric discharge is an aspect of silo design of major importance. In this study, the wall loads during the eccentric discharge was investigated by performing a range of DEM simulations for a coal silo with two outlets when only one outlet is in operation. Apart from the information regarding the flow patterns developed during discharge and the corresponding normal wall loads that are generated, the simulations enable an appreciation of the transient flow patterns that occur as the stress fields change from 'active' to 'passive' states when flow is initiated. Of particular interest are the distributions of the normal pressures around the periphery of the silo wall at a height defined as the 'critical transition' where the flow down the wall converges as a result of a "hopper type" flow channel forming above the cylinder/hopper transition. The wall loads distribution has been investigated under two situations, namely, with or without localized dead zones due to build-up of bulk solids within the silo. The DEM results indicate that the wall loads on the side furthest from the eccentric discharge location are larger than those on the side nearest the eccentric discharge location, the results being comparable to those derived from AS3774 (1996) and EN 1991-4 (2006). The DEM results also show the significant variation in the wall load distributions which could affect the structural integrity of the silo. The DEM simulations are also used to explore the effects of particle-wall frictional coefficient.