Discrete Element Method (DEM) is a numerical technique for predicting the behavior of bulk solids. A bulk solid is a large collection of solid particles; otherwise known as granular media. Some examples of granular media flows include grains being moved through processing equipment, ore being passed through mining machinery, and sand falling through an hourglass. Granular media flow can be quite complex as these flows are known to exhibit solid-like, fluid-like, or a combination of both behaviors. For example, sand in an hourglass behaves like a fluid while a stockpile of sand can have a solid-like stress-strain response.

DEM is a mesh-free method and does not solve the continuum equations of motion. Hence, no stress-strain constitutive law for the material is needed. Instead, a stress-strain relationship can be obtained as an output from the DEM model. A general DEM algorithm is shown below:

Figure 1.1: Schematics of a typical normal force–overlap response for the hysteretic linear spring model.

The equations of motion for every individual particle are numerically integrated with time. For this process, the total force on a particle needs to be known. The total force is the resultant of contact forces (between particles and with the boundary) and body forces. Typical body forces are gravity (weight), fluid and other forces, such as electrostatic, electromagnetic, and so on.