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Indexed by:期刊论文

Date of Publication:2021-01-30

Journal:POWDER TECHNOLOGY

Volume:339

Page Number:534-549

ISSN No.:0032-5910

Key Words:Discrete element method (DEM); Super-quadric particle; Triangular element; Non-linear contact model; Hopper discharge

Abstract:Super-quadric elements based on continuous function representation can be used to construct the geometric shape of irregular particles accurately. Although the contact detection of these elements has been well established, in real industrial applications, the geometric boundaries are complex and cannot be described by a specific function. A common and popular approach is to use a standard triangular finite-element surface mesh. In this work, the interaction between super-quadric particles and triangular elements is discussed in detail. Because the shapes and surface curvatures differ under the various contact patterns between super- quadricparticles, the linear contact force model cannot be used to calculate the contact force accurately; therefore, a corresponding non-linear force model is extended to super-quadric particles. In this model, the equivalent radius of curvature at a local contact point is introduced to calculate the normal contact force, and the tangential contact force is simplified based on the contact model of the spherical elements. To examine the validity of the algorithms and this model, three tests are performed. The first consists of a comparison against theoretical results for a flat wall impacted by a single cylinder-like particle with different blockiness parameters. In the second, the continuity of the contact force when a particle slides from one triangular element through the shared edge or the shared vertex to the neighboring element is tested. In addition, the three contact modes are counted in a boundary model represented by several triangular elements, and compared with the previous numerical experiments. The last tests consist of comparisons against experimental results of the arch structure of cube-like particles and the dynamic hopper discharge of ellipsoids. These studies demonstrate that the proposed method and force model are reliable and applicable for the dynamic hopper discharge of non-spherical particles. Furthermore, the effects of particle shapes, base angles, and friction coefficients on the discharge rate are discussed. The results show that the discharge rate always decreases with decreasing base angle or increasing blockiness, particle friction, or aspect ratio (from 0.5 to 1.5). Moreover, the influences of the base angle, the friction coefficient, and the blockiness on the flow rate are the primary factors, whereas the aspect ratio has a secondary effect on the flow rate. Finally, the packing fraction and the probability density functions of the normal contact force at the initial moment are analyzed to demonstrate the effect of blockiness on the macroscopic discharge rate. (C) 2018 Elsevier B.V. All rights reserved.