Enhanced Mesh-Free Simulation of Regolith Flow

NASA needs simulation tools capable of predicting the behavior of regolith in proposed excavation, transport, and handling or sample acquisition systems. For engineering-scale problems FE analyses utilizing soil-mechanics-based constitutive models have long been utilized in civil engineering to evaluate stresses and deformations up to failure, even including some plastic flow. The extremely large strains, bulking and recompaction behavior in excavation, hopper flow and regolith processing, however, are generally beyond the capability of most FE codes. Mesh-free methods offer an attractive option especially when coupled with critical-state soil-mechanics based constitutive models allowing unlimited shear deformation and flow. This Phase-1 project will enhance a new mesh-free SPH-based simulation model, initiated as part of an earlier SBIR project, to demonstrate its potential to meet NASA's need for a robust simulation tool for regolith manipulation and flow. Enhancements include providing smooth transitions as new free surfaces are created, parallelized algorithms so that high resolution can be maintained as the physical scale of the problems is increased to realistic engineering sizes, and inclusion of realistic cohesion in the critical-state soil-mechanics constitutive model. The large fraction of very fine particulates in lunar and Martian regoliths (e.g., particles < 20-microns) precludes particle-scale DEM models from ever being able to both maintain particle-scale fidelity and simulate engineering-scale problems. Utilization of larger-than-nature 'calculational particles' in DEM code leads to new challenges calibration of those 'particles' so that the calculational material will reproduce the constitutive behavior of the original granular assembly. The mesh-free SPH model developed here has the potential to become a new robust simulation tool to address NASA's challenging regolith manipulation and flow problems.

The pharmaceutical industry has a large number of applications, which would benefit from significantly improved simulation capabilities for cohesive powders in a variety of pharmaceutical material manufacturing, transport and handling operations. The FDA's Process Analytical Technology (PAT) initiative emphasizes the need for pharmaceutical makers to understand the processes they use and to design the processes for quality, reliability, robustness and consistency. These goals overlap significantly with NASA's needs to better understand the processing of bulk cohesive granular material. Reliable tools to predict powder deformation and flow behavior would greatly facilitate the attainment of such goals.

New high-fidelity simulation tools for cohesive powders will be applicable to a wide range of ISRU situations including excavation, transport, handling, platform mobility, slope stability and wheeled vehicle traction analysis. New designs in all of these areas will benefit from improved robustness and fidelity of simulation models. The ability to test sensitivity of equipment designs to regolith model parameter values, can greatly assist in prioritizing regolith characterization measurements and subsequent optimization of equipment designs once the properties of the regolith have been more accurately characterized. Constitutive models specially designed for very low consolidation states of regolith (which can occur in reduced gravity environments such as on lunar or asteroid surfaces) will provide new capability for simulation and engineering analysis of tools and mission hardware including sample acquisition and handling.

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