SIMULATION OF MAGNETIC GRANULAR MEDIA USING OPEN SOURCE SOFT SPHERE DISCRETE ELEMENT METHOD

Abstract

Magnetic granular media were investigated using a mutual dipole magnetic model integrated into the open source Soft Sphere Discrete Element Method (DEM) framework LAMMPS and LIGGGHTS. Using the magnetic model and the contact force models from LIGGGHTS, we simulated shear behavior of MagnetoRheological Fluids (MRF). We found that the size distribution of simulated particles significantly affects the qualitative and quantitative behavior of MRF in a simple shear cell. Additionally, including cohesion, rolling resistance, friction and other contact forces affect the simulated shear behavior. By using a high fidelity contact force model along with an accurate size distribution and the mutual dipole magnetic model we were able to accurately match experimental data for an example MRF.We used the DEM model to aid in the development of a novel MRF valve operating on an alternative MRF behavior. Our jamming, MRF valve holds pres- sure through stable, but reversible jamming in the flow path, and is actuated by electropermanent magnets, which require no quiescent current to maintain their magnetization states. These valves do not require the large power draw of con- ventional MRF valves to maintain their state. We were able to accurately predict the experimental jamming behavior of the MRF valve using Finite Element Analysis and LIGGGHTS with magnetization, further validating the model with a non-linear, non-continuum behavior. Our jamming MRF valve was demonstrated in a multi- segmented, elastomeric robot, actuated using MRF. Using the magnetic DEM model coupled with self-gravity, the effects of mag- netism on rubble pile magnetic asteroids were examined. We simulated formation, and disruption of metallic asteroids with remnant magnetizations using LAMMPS with permanent dipoles. We found that rubble pile asteroids, formed from clouds of magnetized grains, coalesce more quickly, and have higher porosities than aster- oids coalesced from unmagnetized grains. Distortion and disruption was affected by magnetization during simulated YORP spin-up. Large fragments with high aspect ratios and low densities were formed from highly magnetized asteroids after disrup- tion, matching the shapes of suspected metallic small bodies. Simulations of grain avalanching on the surface of magnetized asteroids found additional morphological differences from their unmagnetized counterparts, with reduced densities, increased angles of repose, and cornicing.