Flow characteristics of nonspherical granular materials simulated with multi-superquadric elements

Abstract The superquadric equation is typically used to mathematically describe nonspherical particles and construct particle shapes with different surface sharpness and aspect ratios. However, nonspherical elements constructed using the superquadric equation are strictly convex, limiting their engineering application. In this study, a multi-superquadric model based on a superquadric equation is developed. The model combines several superquadric elements that can be used to construct concave and convex particle shapes. Four tests are performed to examine the applicability of the multi-superquadric approach. The first involves a comparison of theoretical results for a single spherocylinder impacting a flat wall. The second involves the formation of a nonspherical granular bed. The third investigates the effects of the particle shape on the hopper discharge and angle of repose. The final test evaluates the mixing behaviors of granular materials within a horizontally rotating drum. These tests demonstrate the applicability of the multi-superquadric approach to nonspherical granular systems. Furthermore, the effects of particle shape on the packing density, discharge rate, angle of repose, and Lacey mixing index are discussed. Results indicate that concave particles have a lower packing density, flow rate, and mixing rate and higher angles of repose than convex particles. Interlocking of elements becomes more pronounced for concave particles and results in local cluster structures, thereby enhancing the stability of granular systems and limiting sliding or rotation between nonspherical particles.