Confined binary particle mixing with a modified discrete element method

A modified version of a nonlinear viscoelastic damping model is presented to better represent overall spherical particle response using the discrete element method (DEM) to simulate gravity-driven mixing of binary particles into a confined box. Nonlinear springs are used in the normal and tangential directions to simulate the contact forces, and an additional nonlinear annular spring is employed at the contact points to account for rolling friction. A viscous damping term related to the relative motion between contacting particles is applied to represent energy dissipation, and an alternative condition for checking the end of a collision is applied. The new model is shown to successfully recover the tangential force behavior in stick and sliding regions without having to introduce more complicated behavior. Results are in excellent agreement with existing benchmark tests, and the model is applied to evaluating several different mixing schemes using fixed geometric particle flow disruptors with sometimes surprising results.