CFD–DEM simulation of collapse dynamic mechanisms of partially immersed granular columns

Partially immersed granular materials are widely present in both geophysical processes and industrial environments. Granular materials partially immersed in a fluid experience additional hydrodynamic resistance, which significantly alters their dynamics. Furthermore, the process of particles crossing the air–water interface involves complex fluid dynamic interactions. In this study, we conduct a numerical investigation of the collapse process of partially immersed granular columns using a coupled CFD–DEM model. The validity of the numerical model is confirmed by comparing the results with existing experimental data. The simulation results reveal that the collapse of partially immersed granular columns exhibits unique characteristics. Through an analysis of the collapse process, energy evolution, and fluid drag characteristics, we identified an additional fluid resistance mechanism near the interface. This mechanism inhibits the conversion of vertical kinetic energy into horizontal kinetic energy, thereby reducing the final run-out distance. Moreover, we have revised the scaling laws for the final run-out distance and final deposit height by incorporating the effects of water depth and density ratio.