Abstract: This talk discusses developments in continuum modeling and hybridized discrete- continuum modeling for fluid-saturated and dry particle flows. First, we discuss a methodology for simulating "simple" continuum models for dry grains, focusing on a recent frictional plasticity model and a meshfree simulation approach using the Material Point Method (MPM). This approach on its own is shown sufficient to describe a number of granular intrusion problems.

However, due to its simplicity such a model cannot always be trusted to capture general flows accurately, and struggles to represent particle-scale phenomena such as clogging, shear-banding, ballistic motion, and particle-wall tribology. To address this we propose a discrete-continuum hybrid approach, where an "oracle" algorithm adaptively decides how to partition the domain into continuum regions and discrete element regions. The idea is to use continuum modeling (MPM simulation) in sub-regions where it can be trusted, and the discrete element method (DEM) in sub- regions where additional clarity is needed. The domains overlap along transition zones, where a Lagrangian dynamics mass-splitting coupling principle enforces agreement between the two simulation states. Enrichment and homogenization operations are developed that allow the partitions to evolve over time. This approach accurately and efficiently simulates complex scenarios that previously required an entirely discrete treatment.

Finally, we discuss a technique for submerged granular flow problems, which treats the granular phase and the fluid phase as two separate, yet coupled continuum models. Using mixture theory, the forces of bouyancy and drag couple the Navier-Stokes behavior of the fluid phase to a dilatant, rate-sensitive granular flow continuum model. The final mixture formulation is simulated using two coupled MPM simulations, one for the fluid phase and one for the granular phase, which solves for all continuum variables in all phases. This methodology is shown able to replicate experimental results for saturated granular flows over a range of conditions and dilutions, and can be extended to account for more obscure effects, including the dramatic shear-thickening seen in fine-particle suspensions such as cornstarch-and-water mixtures.