A novel particle tracking method for granular sands based on spherical harmonic rotational invariants

Abstract

Particle tracking is an important technique used to gain insights regarding the particle kinematics of deformed sand specimens subjected to in situ X-ray micro-computed tomography (μCT). The present study proposes a novel particle tracking method based on the multiscale matching of the morphological features of sand particles. First, a set of spherical harmonic (SH) invariants was introduced to describe the multiscale morphological features of sand particles. Next, a particle matching algorithm was proposed to evaluate the morphological similarities between the particles at different states by examining the second-order norm differences in the SH invariants. Finally, the particles at different states could be tracked once a minimum difference in the SH invariants was identified. The efficiency of this tracking method was validated in a case study, wherein a sand specimen was subjected to high-resolution μCT scanning at an initial state and again at a state of large deformation. The particle tracking results obtained from the SH-based and volume-based methods confirmed the efficiency and robustness of the proposed particle tracking method for tracking the particle kinematics within a sand specimen subjected to large deformation.