Deposition and shaking of dry granular piles

A friction force model describing reversible stick-slip transition during contact has been developed with the special purpose to simulate the deposition of granular material. A test with a mass on a conveyor belt kept in position by a spring shows that a numerical simulation of the dynamics of such a type of system produces the same behaviour as the analytical solution. Next by numerical simulation the deposition of granular material on a free horizontal surface or in a container is studied. At the end of this deposition process a stable pile is formed. In addition such a pile can be shaken in horizontal or vertical direction. Then the pile becomes unstable and depending on the type and the intensity of shaking a characteristic type of motion is observed.<o:p></o:p></span><p class=MsoNormal style='text-align:justify;line-height:130%'><span lang=EN-GB style='font-size:12.0pt;mso-bidi-font-size:10.0pt;line-height:130%'><o:p> </o:p></span><p class=MsoNormal style='text-align:justify;line-height:130%'><span lang=EN-GB style='font-size:12.0pt;mso-bidi-font-size:10.0pt;line-height:130%'>For two and three-dimensional structures of dropping granular material the dynamical mechanisms, and consequently, the shape and internal structure of the deposited piles are highly different. In 2D there is a large-scale internal motion, that can be characterised as landslides along fault lines in an almost regular triangular pile. In 3D there are no landslides, but small internal shifts in a loosely random stacked conical pile. In both 2D and 3D surface avalanches are observed. Also in both dimensions the slope of the pile increases with the number of granular particles. Moreover, the slope increases with the coefficient of dynamic friction, and decreases with the coefficient of restitution. In the literature the presence of a dip of the normal force at the bottom surface is reported. Such a dip being the result of an arc like structure of granular material in the interior of the pile near the centre at the bottom is not systematically found in our simulations