DEM analysis of friction of cylindrical pinewood pellets with corrugated steel silo walls

Steel silos with corrugated walls exhibit friction phenomena between the bulk material and the silo wall quite different from those produced in smooth walls. A silo model was designed, and discrete element method (DEM) simulations were performed to analyze an influence of the depth and wavelengths of corrugations on mass flow rate, wall pressures, location of the shear band and effective wall friction coefficient. The dimensions of the geometry adopted correspond to one of the vertical sections of the silo model with corrugated steel walls instrumented by the authors. This silo model consisted of a square cross section (0.45 x 0.45 \(m^2\)) and 0.75 m in height, a flat bottom with a centric, square outlet (0.06 x 0.06 \(m^2\)), corrugated lateral steel walls, and smooth, transparent methacrylate front and back walls. The bulk material was pinewood pellets, whose mechanical and numerical properties had been previously obtained by the authors. The numerical results show an influence of the depth of corrugation and the wavelength on the velocity of the granular particles and the friction forces against the wall. The initial position of the shear band was found to be placed between 1 and 3.5 times the average size of the particles from the vertical line connecting two consecutive corrugation peaks closest to the silo outlet. The effective wall friction coefficient for corrugated walls depends on the wavelength and the depth of the corrugations, varying in the range of 0.42 to 0.9, in opposition to the single theoretical value of 0.78 proposed by Eurocode EN 1991-4, for a sinusoidal profile, regardless of the geometrical parameters.