Abstract
Arching in dry granular material is a long established concept, however it remains still an open question how three-dimensional orifices clog. We investigate by means of numerical simulations and experimental data how the outflow creates a blocked configuration of particles. We define the concave surface of the clogged dome by two independent methods (geometric and density based). The average shape of the cupola for spheres is almost a hemisphere but individual samples have large holes in the structure indicating a blocked state composed of two-dimensional force chains rather than three-dimensional objects. The force chain structure justifies this assumption. For long particles the clogged configurations display large variations, and in certain cases the empty region reaches a height of 5 hole diameters. These structures involve vertical walls consisting of horizontally placed stable stacking of particles.
Highlights
With the help of discrete element (DEM) simulations one can quantitatively compare the morphology of clogging arches with experimental data, and accurately map the force distribution inside the silo [1, 2]
In the present work we identify the blocking structure in three-dimensional hoppers with DEM simulations focusing on particle configurations and forces and compare our finding to our measurements using X-ray computed tomography
The number of spheres required to build up a long particle was varied to prevent linear gear effect
Summary
Discharge of silos and the flow of granular material through orifices are important questions of everyday life and technological processes. In 2D it is straightforward to define the blocking arch by finding a continuous chain of particles from one side of the orifice to the other. One can visualize the force network and the structure of the arch experimentally by using photoelastic particles [3, 4]. With the help of discrete element (DEM) simulations one can quantitatively compare the morphology of clogging arches with experimental data, and accurately map the force distribution inside the silo [1, 2]. In the present work we identify the blocking structure in three-dimensional hoppers with DEM simulations focusing on particle configurations and forces and compare our finding to our measurements using X-ray computed tomography. We compare the case of spherical particles with elongated grains
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