Geometric Origin of Macroscopic Alignment in Granular Flows
Abstract
Predicting the alignment of non-spherical particles in dense granular flows under shear remains a central challenge in soft matter physics. We demonstrate that the first-order behavior of granular fabric,the anisotropic distribution of contacts, is a direct consequence of particle boundary geometry. By assuming uniform contact probability along a particle's perimeter, we derive a mapping between local curvature and the macroscopic distribution of contact normals. This minimal geometric framework accurately predicts the uniaxial nematic order parameter S2 observed in both three-dimensional discrete element simulations and laboratory experiments using various particle geometries (e.g., rice, fibers, and disks) across a wide range of aspect ratios. Our results show that particle shape dictates the available orientation statistics, providing a purely geometric baseline for the emergence of fabric in dense granular systems.
Cite
@article{arxiv.2605.28633,
title = {Geometric Origin of Macroscopic Alignment in Granular Flows},
author = {Christopher Harper and Eric C. P. Breard and George W. Bergantz and PJ Zrelak},
journal= {arXiv preprint arXiv:2605.28633},
year = {2026}
}