  An adpative integration technique for time advancement of particle motion in
the context of coupled computational fluid dynamics (CFD) - discrete element
method (DEM) simulations is presented in this work. CFD-DEM models provide an
accurate description of multiphase physical systems where a granular phase
exists in an underlying continuous medium. The time integration of the granular
phase in these simulations present unique computational challenges due to large
variations in time scales associated with particle collisions. The algorithm
presented in this work uses a local time stepping approach to resolve
collisional time scales for only a subset of particles that are in close
proximity to potential collision partners, thereby resulting in substantial
reduction of computational cost. This approach is observed to be 2-3X faster
than traditional explicit methods for problems that involve both dense and
dilute regions, while maintaining the same level of accuracy.
