> For the complete documentation index, see [llms.txt](https://2025.istvs.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://2025.istvs.org/submissions/papers/4122.md). # 4122 - DEM ANALYSIS OF EFFECT OF INTERPARTICLE FORCES ON SAND-OUTFLOW BEHAVIOR FROM HOPPER UNDER LOW-GRAVITY ENVIRONMENT {% hint style="info" %} Paper presented at ISTVS 2025 | 55th Conference of the International Society for Terrain-Vehicle Systems {% endhint %} **Authors:** *Shunsuke Muryokoji, Shingo Ozaki* **Keywords:** Microgravity; Discrete Element Method (DEM); Van der Waals Force; Electrostatic Force; Hourglass **Abstract:** Understanding the behavior of granular materials under various low-gravity conditions is essential for planetary exploration, as it impacts lander interactions, rover mobility, and in-situ resource utilization processes. However, ground-based experiments using parabolic flights and drop tower facilities are limited by short-duration microgravity conditions, making it challenging to fully capture behavior of granular materials. To address this, numerical simulations provide a powerful alternative. This study employs the discrete element method (DEM) to simulate sand-outflow behavior from hoppers under reduced gravity, based on the Hourglass experiment conducted aboard the International Space Station (ISS). The experiment utilized artificial gravity (0.06G–2G) to observe the deposition and flow characteristics of different granular materials. Using the DEM, we modeled silica sand samples (#5 and #8), incorporating contact forces, rolling resistance, and van der Waals forces/electrostatic forces to evaluate their impact on particle motion. The results show that silica sand #5 exhibited minimal adhesion effects, whereas silica sand #8 demonstrated significant accumulation of sand on walls, particularly under lower gravity conditions. Moreover, neither van der Waals nor electrostatic forces alone could fully replicate experimental results, indicating that both must be considered for accurate modeling. These findings emphasize the importance of interparticle forces in regolith behavior under low gravity and provide insights into granular material interactions in extraterrestrial environments. This study could contribute to the design and optimization of robotic systems for planetary exploration, particularly in excavation, mobility, and construction applications. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://2025.istvs.org/submissions/papers/4122.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.