Modeling of Tire and Regolith Interaction for Surface Mobility Applications

Exploration and eventual habitation of the surface of the Moon and Mars are highly dependent on our ability to safely and efficiently navigate the complex terrain and terramechanical response of the environment on vehicles and machinery. NASA has awarded contracts to develop new Lunar Terrain Vehicles (LTVs) to transport astronauts and essential equipment during future missions with required ranges of up to 5 km. Designing LTVs that sustain operation in this harsh environment is difficult, especially for LTV tires, which must be designed to operate in soil that behaves vastly different than terrestrial soils. Mimicking the Lunar/Martian environment and capturing the complex terramechanics of the soil and tire in experiments is limited, and designers must turn to computational approaches to study these interactions. Classical terramechanics models are useful to a degree but fail to properly capture behavior of compliant tires commonly used for LTVs. On the other hand, Lagrangian Discrete Element Methods (DEM) can capture per-particle regolith interaction with the tires with high accuracy but at significant computing cost thus limiting use for full-scale problems. CFD Research aims to address this modeling gap using a coupled DEM-informed Eulerian-Eulerian approach to simulate the regolith with DEM-based compliant tire models. Eulerian-Eulerian methods model a ‘granular’ volumetric fluid with constitutive models, thus significantly reducing the computational burden of having to track billions of particles required for DEM. DEM-tire models will use bond models to simulate compliant tires, which in turn is less expensive than traditional finite element approaches. The developed capability will be validated against experiments and verified against ‘Project Chrono ’ soil contact model and a DEM soil model. The resulting tools will facilitate performance analysis of a wheel-based (rigid and compliant) surface mobility system traversing a realistic compound slope condition.