A numerical hopper discharge study for convex and non-convex particle systems

Computing efficiently with non-spherical particles in discrete element simulations remains a challenging endeavour. To complicate matters further, it is often required to resolve particle angularity and non-convexity as has been demonstrated experimentally to be important for a number of applications. Angularity is achieved by modelling particles as polyhedra as opposed to the conventional multi-sphere particles or more recently superquadrics. The latter two approaches introduce rounded edges that may result in an insufficient description of angularity for some applications. Fortunately, the last decade has seen the computation of polyhedral convex particles in discrete element simulations, which of late are often being accelerated by computing on general purpose graphical processing units (GPGPUs). However, the computation of non-convex polyhedral particles has remained elusive with a limited number of studies that have been conducted towards this aim, albeit the importance of the mechanical interlocking that results from particle non-convexity has been well known for years. This study demonstrates the importance of modelling particle non-convexity for hopper discharge applications, in particular, we highlight the validation against a hopper flow experiment, using identical convex and identical non-convex 3D printed particles. Thereafter we conduct a numerical investigation into the discharge and force chain development for three discharge openings using convex and non-convex particle systems. Significant differences in discharge is evident for the smaller openings between convex and non-convex particle systems. In addition, differences in the development of inter-particle force chains is also evident between convex and non-convex particle systems.