(189q) Force Model Concerns for Glued Sphere Dem Simulations

Kodam, M., Purdue University
Bharadwaj, R., Pfizer Inc.

Despite knowing that particle shape plays a significant role in the dynamics of powder flow, most discrete element method (DEM) simulations utilize spherical particles. The reasons for using spherical particles are that (a) the contact detection scheme for spherical particles is simple, and (b) the contact force models for contacting spheres are well known (e.g. a Hertzian contact).

Several schemes for modeling non-spherical particles have been proposed including those that concern polyhedra, ellipsoids, sphero-cylinders, and superquadrics. Perhaps the most common approach for modeling non-spherical particles, however, is using ?glued spheres,? in which irregular particle shapes are produced by rigidly connecting individual, and possibly overlapping, spheres. The advantage of the glued spheres approach is that even for complex particle shapes the simple spherical contact detection algorithm may be retained.

Recent publications have focused on how approximating a given particle shape using a glued sphere geometry affects the rebound of colliding particles (e.g. Price et al., 2007 and Kruggel-Emden et al., 2008). These investigations have focused on the errors introduced by approximating the geometry of the true particle shape. What has not been investigated, however, is how the spherical particle derived force models used in glued sphere particle geometries influence the response of particle collisions. This paper demonstrates that in instances where more than a single component sphere in a glued sphere model is involved in a contact, a modified force model must be used to produce an accurate force-deflection response.