DEM Simulations of the Effects of Particle Shape, Interparticle Cohesion, and Gravity on Rotating Drum Flows of Lunar Regolith

Abstract

Discrete Element Method (DEM) simulations of rotating drum flows, aimed at developing simulation models for the deformation and flow of lunar regolith, tested the effects of particle shapes (spheres, particles comprised of 8-spheres in a cubical arrangement, and clusters of 4-spheres in a tetrahedral arrangement) and a variety of cohesive pull-off force values. In these simulations the calculational-material comprised of purely spherical particles flowed much more readily than did the regolith simulants being used as guides for this study. The simulated samples comprised entirely of cubical-cluster particles appeared to have higher shear resistance than observed in physical tests of JSC-1A simulant. The samples comprised of tetrahedral cluster particles responded in a manner that most closely resembled the observed behavior of the simulant powder. Linear, quadratic and cubic scaling of the model cohesive pull-off force parameter with particle size was examined to see which scaling with particle size would come closest to preserving the overall mode of the bulk powder flow if larger-than-nature calculational particles were used in the simulations. Theoretical cohesive force models, such as JKR or DMT, predict that actual pull-off forces due to van der Waals interactions acting between particles will scale linearly with particle size. The aim of this study was to see what scaling of the cohesive force with particle size would allow larger calculational particles to exhibit bulk deformation similar to a material comprised of much smaller physical particles. Not unexpectedly it was found that scaling the pull-off force parameter with the square of the particle-size produced flows that remained the most similar, as the size of the calculational particles was increased. This scaling keeps the bulk tensile strength per unit area of the bulk powder approximately constant as the calculational particles vary in size. BACKGROUND