Discrete particle simulation of a sand flow under artificial low-gravity conditions: Analysis of the competitive relationship between gravity and adhesion

The evaluation of the characteristics of a sand flow under low gravity has a considerable impact on operations on the surfaces of extraterrestrial bodies. In this study, simulations of the sand flow and sedimentary behavior of a hopper under low gravity were performed using the discrete element method, with reference to the results obtained during the Hourglass mission in the International Space Station. A combination of the van der Waals and contact models was used to successfully reproduce the competing relationship between gravity and adhesion observed in the low-gravity experiment. It was shown that the grain size distribution is a critical factor in sand flow behavior in a low-gravity regime, where the effect of adhesion becomes dominant. Furthermore, it was demonstrated that the floating of the agglomerating sand clumps exposed to a weightless environment observed in the experiment could be reproduced using the obtained parameter set. The obtained results can contribute to various operations in future space exploration, including in-situ resource utilization (ISRU).