3:45 PM - 4:00 PM
[PPS02-02] Laboratory and numerical study of the behavior of angular particles under vibration: Implications for the formation and evolution of small bodies
Keywords:Granular materials, convection, Particle shape, Angularity
Asteroids visited by spacecraft have been found to be covered with loose granular materials known as regolith. The properties of granular materials have been studied in a variety of fields, and many of these studies use spherical particles for simplicity, which is also the case when studying small bodies. However, recent work has suggested that the particle shape has a significant effect on the behavior of granular materials. Therefore, we need to investigate whether the effect of particle shape should be considered when studying the formation and evolutionary processes of small bodies.
In this study, we focus on the behavior of granular materials under vibration, since the seismic shaking is one of the most common phenomena occurring on the surface of small bodies. To study the effect of particle shape, we introduce the particle angularity, which is defined as the ratio of sphericity to the number of vertices of a polyhedron. We prepare spherical (i.e., low angularity) and polyhedral (i.e., high angularity) particles, and compare their behavior by performing both laboratory experiments and numerical simulations. In the experiments we fill a cylindrical container having a diameter of 140 mm with approximately 24,000 mono-sized particles. The container is vibrated at an amplitude of 0.5 mm and a frequency of 50 Hz. The numerical simulations are performed under the same conditions as the experiments.
The results from both experiments and numerical simulations show that the higher the angularity, the more likely convection is to continue. This may be because particles with lower angularity experience a reduction in interparticle voids due to vibration (i.e., compacted), exhibiting solid-like behavior. On the other hand, particles with higher angularity maintain a structure with larger interparticle voids, allowing particle convection to continue.
We also find that the effect of particle shape cannot be fully reproduced by the rolling resistance model, which is commonly used in the DEM simulations to account for the effects of non-spherical particles. This indicates that the effect of angularity is owing to the geometry of the particles rather than due to limitations in their mobility. These results suggest that fluidization may occur more easily in natural granular materials than predicted by numerical simulations using spherical particles.
In this study, we focus on the behavior of granular materials under vibration, since the seismic shaking is one of the most common phenomena occurring on the surface of small bodies. To study the effect of particle shape, we introduce the particle angularity, which is defined as the ratio of sphericity to the number of vertices of a polyhedron. We prepare spherical (i.e., low angularity) and polyhedral (i.e., high angularity) particles, and compare their behavior by performing both laboratory experiments and numerical simulations. In the experiments we fill a cylindrical container having a diameter of 140 mm with approximately 24,000 mono-sized particles. The container is vibrated at an amplitude of 0.5 mm and a frequency of 50 Hz. The numerical simulations are performed under the same conditions as the experiments.
The results from both experiments and numerical simulations show that the higher the angularity, the more likely convection is to continue. This may be because particles with lower angularity experience a reduction in interparticle voids due to vibration (i.e., compacted), exhibiting solid-like behavior. On the other hand, particles with higher angularity maintain a structure with larger interparticle voids, allowing particle convection to continue.
We also find that the effect of particle shape cannot be fully reproduced by the rolling resistance model, which is commonly used in the DEM simulations to account for the effects of non-spherical particles. This indicates that the effect of angularity is owing to the geometry of the particles rather than due to limitations in their mobility. These results suggest that fluidization may occur more easily in natural granular materials than predicted by numerical simulations using spherical particles.