Collaborative Research: ISS: Gravity-Dependence of Dense Granular Flows: Experiments and Digital Twins

Materials made of grains - like sand, agricultural products, and pharmaceutical powders - are not only some of the most common materials in our daily lives but also cover the surfaces of other planets. Predicting how they will flow on Earth has been a long-standing challenge for engineers. These difficulties will only grow as missions are planned at lower gravity to explore asteroids, the Moon, and Mars. In this project, the team will create powder-flow experiments small enough to fly on the International Space Station. These experiments, performed by astronauts at both high and low gravity, will be compared to results from experiments performed by students here on Earth. Using this data, reliable digital twins will be created and tested, which are computer models that mimic the observed flows. Through these efforts, cutting-edge training will also be provided to students. This project will explore granular flow behavior by conducting and modeling experiments under different gravity conditions, both on Earth and aboard the International Space Station (ISS) using the Multi-use Variable-gravity Platform (MVP). This specialized facility employs a centrifuge to simulate a wide spectrum of gravitational forces - from near-weightlessness to conditions exceeding Earth gravity - offering a rare opportunity to examine how granular systems respond outside typical terrestrial environments. This project will investigate two central hypotheses. The first posits that granular flows are strongly influenced by the magnitude of gravity. To test this, rotating drum flows composed of materials ranging from uniform beads to regolith simulants will be analyzed. By examining features like interface geometry and internal velocity fields, it will be determined whether observed behaviors follow theoretical predictions for gravity-dependent scaling laws, or deviate in measurable ways. The second hypothesis suggests that existing continuum modeling frameworks, grounded in fundamental mechanics, can be extended to accurately capture granular dynamics in low-gravity regimes. These conditions may amplify secondary effects such as cohesion or particle softness, which will be incorporated by the team into model refinements. Using data from both ground and ISS experiments, the team will iteratively calibrate and validate the models. Success will be defined by identifying dominant constitutive ingredients across different gravity levels. This will provide crucial evidence that well-constructed continuum models can serve as predictive digital twins for granular processes relevant to planetary exploration, where direct experimentation is limited or impossible. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.