DEM simulation of packing mono-sized pebbles into prismatic containers through different filling strategies

The packing structure of the pebbles influences the thermo-mechanical behavior of the pebble beds in fusion breeder blankets. The packing structures at the wall of the container plays an important role in the extraction of heat energy out of the pebble bed to the surroundings. The packing fraction varies from the wall to the bulk region (away from wall). Hence, it is essential to understand the variation of packing fraction across the pebble bed. Packing structures were previously studied through X-ray tomography experiments and computer simulations. Computer simulations of packing were done using random closed packing algorithm, but without considering the gravity effect. Such simulations were able to predict only the wall-effect. In this paper, the packing structures are generated using discrete element method (DEM) by pouring the pebbles into prismatic containers under gravity. DEM simulations reveal that the extent of wall effect on the packing structure is not the same in all the directions. Due to the presence of gravity, the bottom wall (i.e. in the direction of gravity) induces regular packing up to 6 layers while the lateral walls influence is seen only up to 4 layers. Further, it is shown that the packing structure is also influenced by various filling strategies. The present work studies the evolution of packing structure through various filling strategies with an emphasis on the extent of wall effect on the packing structure.