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Developments in Discrete Element Methods for Rail Ballast Modeling

In this work new developments for the advancement of Discrete Element Methods (DEM) are formulated and verified. Discrete Element Methods (DEM) are most suitable for modeling and dynamic simulations of granular material. By nature this family of methods, tends to become computationally expensive for large problems and their efficiency depends primarily on the efficiency of associated time integration schemes, and the efficiency of contact detection and particle interaction force algorithms. This work presents two techniques for improving the efficiency of the DEM methods.  The first technique adapts a semi-implicit time integration scheme that has been reported in the literature for structural dynamics applications and implements it within the DEM framework. The proposed method is shown to be unconditionally stable and to reduce execution times for the same level of accuracy as conventional techniques currently used in the DEM. The method is verified with existing techniques and assessment studies on accuracy, stability, and computational efficiency have been conducted. The implementation of the proposed method is discussed and demonstrated through showcase problems.  The second technique implements the Boundary Element Method (BEM) for elastostatic problems within the context of computing contact forces between particles in the DEM. The proposed technique has the capability to model arbitrarily shaped particles, where, analytic solutions do not exist for the purpose of computing contact forces. In addition this method can easily be implemented with any time marching scheme used to solve the equations of motion. An innovation of the proposed method is the development of the Interior Constraint BEM (ICBEM) formulation that computes elastostatic solutions of particles without proper boundary constraints which, in general, exhibit rigid body motion. The proposed techniques are verified through Finite Element Solutions and with the classical Johnson contact theory.

Funding agency: 
ART Group; CEE Department