  Granular dynamics driven by fluid flow is ubiquitous in many industrial and
natural processes, such as fluvial and coastal sediment transport. Yet, their
complex multiphysics nature challenges the accuracy and efficiency of numerical
models. Here, we study the dynamics of rapid fluid-driven granular erosion
through a mesh-free particle method based on the enhanced weakly-compressible
Moving Particle Semi-implicit (MPS) method. To that end, we develop and
validate a new multi-resolution multiphase MPS formulation for the consistent
and conservative form of the governing equations, including particle
stabilization techniques. First, we discuss the numerical accuracy and
convergence of the proposed approximation operators through two numerical
benchmark cases: the multi-viscosity Poiseuille flow and the multi-density
hydrostatic pressure. Then, coupling the developed model with a generalized
rheology equation, we investigate the water dam-break waves over movable beds.
The particle convergence study confirms that the proposed multi-resolution
formulation predicts the analytical solutions with acceptable accuracy and
order of convergence. Validating the multiphase granular flow reveals that the
mechanical behavior of this fluid-driven problem is highly sensitive to the
water-sediment density ratio; the bed with lighter grains experiences extreme
erosion and interface deformations. For the bed with a heavier material but
different geometrical setups, the surge speed and the transport layer thickness
remain almost identical (away from the gate). Furthermore, while the
multi-resolution model accurately estimates the global sediment dynamics, the
single-resolution model underestimates the flow evolution. Overall, the
qualitative and quantitative analysis of results emphasizes the importance of
multi-scale multi-density interactions in fluid-driven modeling.
