Comparison of multi-sphere and superquadric particle representation for modelling shearing and flow characteristics of granular assemblies

Abstract

In the current study, complex-shaped particles are simulated with the Discrete Element Method (DEM) using two different approaches, namely Multi-spheres (MS) and Superquadrics (SQ). Both methods have been used by researchers to represent the shape of real particles. However, despite the growing popularity of utilizing MS and SQ particles in DEM simulations, few insights have been given on the comparison of the macro scale characteristics arising from the two methods. In this respect, initially the characteristics of the two shape representation methods are evaluated in a direct shear test simulation. The results suggest that controlling the sharpness of the edges for SQ particles can lead to a good agreement with the results of MS particles. This way, a set of SQ and MS particles, which are numerically calibrated in the shear tester, are obtained. Furthermore, the macro-scale responses of the numerically calibrated particles are assessed during a slow shearing scenario, which is achieved through simulating quasi-static flow of the particles from a flatbottom silo. The results for mass discharge, flow profile and wall pressure show a good quantitative agreement. These findings suggest that the numerically calibrated MS and SQ particles in the shear tester can provide similar bulk-scale flow properties. Moreover, the results highlight that surface bumpiness for MS particles and corner sharpness for SQ particles change the characteristics of particles and play a significant role in the shear strength of the material composed of these particles.

Influence of various DEM shape representation methods on packing and shearing of granular assemblies

“…In a previous study [28,29], we have compared the influence of multi-sphere bumpiness and superquadric blockiness on the response of assemblies of cubical particles in several micro-and macro-scale tests. We have observed that singleparticle behaviour is a direct function of both surface and edge properties, and that shape complexity only significantly affects the shear strength, porosity and mode of motion once the packing is dense.…”

DEM study of mechanical characteristics of multi-spherical and superquadric particles at micro and macro scales

“…In this description, spheres are allowed to overlap and be glued together to approximate an arbitrarily shaped particle. On the other hand, irregular particle shapes can alternatively be idealized to some regular shapes such as spheroids, cuboids or cylinders that can be approximated by superquadric (SQ) shapes [9,10,11]. It has been suggested that 80% of all shapes can be represented by superquadric functions or derived from superquadrics in higher-dimensional hyperquadrics [12,13].…”

Flow of anisometric particles in a quasi-two-dimensional hopper

“…On one hand, this might be counterintuitive, as elongated grains undergo shear induced orientational ordering with their average orientation pointing almost in the direction of the flow lines [7][8][9][10][11]. On the other hand, several authors have shown, that for other nonspherical grains increasing grain angularity (or in other words increasing effective friction of the material) reduces the mass flow rate [3,4,[12][13][14][15], and leads to larger stagnant zones and more residual mass after discharge [12,13,16,17]. Several authors detected and quantified fluctuations in the discharge rate or flow field [18][19][20][21].…”