Characterising the shear rate in granular materials using advanced coarse-graining approaches

This study compares two coarse-graining approaches—Artoni and Richard (2015) and Rycroft et al. (2009) —using statistically validated DEM (Discrete Element Method) simulation data and experimental PEPT (Positron Emission Particle Tracking) measurements. DEM and PEPT are fundamentally different in the type of data they provide: DEM data is Eulerian, covering the entire flow field, while PEPT is Lagrangian, tracking the trajectory of individual particles. The coarse-graining methods used also differ in their approaches, with Artoni and Richard spreading each grain’s effect smoothly via a distance-weighted kernel, and the Rycroft method being devoid of any smoothing kernel, instead relying on a least-squares regression. The primary objective of this study is to determine the suitability of each coarse-graining scheme based on the data source—whether DEM or PEPT—and to statistically compare the resultant shear rate continuum fields. By using previously validated high resolution DEM and PEPT data (Moodley and Govender, 2022), we assess the impact of kernel-based and kernel-free coarse-graining methods on shear rate computation. This work contributes to refining continuum descriptions for practical applications by identifying optimal coarse-graining strategies depending on the nature of the underlying data. The shear rate tensor is evaluated in terms of axial and shear components, revealing how coarse-graining choices affect different components of flow behaviour. This research thus bridges the gap between Lagrangian and Eulerian data handling in granular flow studies, enabling accurate modelling of continuum fields in a variety of industrial processes. • Artoni and Richard (2015) and Rycroft et al. (2009) coarse-graining methods compared. • Rycroft et al., (2009) is tuning-free and effective for DEM data. • Artoni and Richard (2015) suits PEPT and DEM when smoothing radius is tuned. • Axial shear components more sensitive to smoothing radius than transverse ones.