Starting from 1990 Frederic V. Donze has developed SDEC, a code based on the Discrete Element Method. This code was based on a newtonian approach using rigid bodies. The elements are described in terms of their mass, volume and interactions. The code herein uses spherical elements. Two elements may be considered as interacting while not touching. Any element within an interaction range of another element defined as a radius around this element will be interacting with the latter. The interactions are known as "soft sphere" interactions because the interaction forces are linked to the displacements of the elements which implies that the elements may penetrate or overlap one another.
Newton's second law of motion describes the motion of each element as the sum of all forces applied on this element. The dynamic behavior of the system is solved numerically by a time algorithm in which the velocities and the accelerations are constant at each time step. The system evolves and an explicit finite difference algorithm is used to reproduce this evolution.
Until now, this code has been used to treat geomechanical problemes in both quasi-static and dynamical applications.
Then, in 2004 SDEC was rewritten from ground-up as a new project YADE which was started by a PhD student Olivier Galizzi. Soon after Olivier has retired, and Janek Kozicki, PhD took the lead of YADE development. It is a free software with a GPL open source licence. It includes the current version of SDEC. At the 3S Lab (University Joseph Fourier), Bruno Chareyre, Wenjie Shiu, Luc Sholtes are using it.