MiMESis-3D

Understanding and predicting snowpack evolution is very important for several applications ranging from climate modeling to avalanche risk forecasting, road viability, water resources availability and management. Snow on the ground is a complex porous material that constantly transforms over time. The evolutions incurred during its metamorphism strongly impact the physical and mechanical properties of the snowpack. Current macro-scale snow models take into account the layered and changing structure of snow, but rely on a very limited set of scalar and largely-empirical parameterizations to describe the full complexity of snow microstructure. Preliminary homogenization approaches to bridge micro and macro scales, relying on 3D snow images obtained by X-ray tomography, have recently made great progress at the international level. However, these approaches remain fundamentally “static” and only provide properties based on the actual observed microstructure. A new and great challenge is to add the dynamic component, i.e., to extend the techniques to the metamorphism effects occurring in the snowpack. The general objective of this project consists in improving the current knowledge and modeling of snow at micro-scale in order to guide the mid-term development of a new generation of snowpack models that better account for metamorphism-induced evolutions of snow microstructure. Through systematic comparisons between 3D numerical modeling and micro-scale experimentations, the project aims at investigating the microscale behavior of snow to better understand and describe the snow physical and mechanical properties at macro-scale. We propose to study the evolution of snow microstructure based on both (1) 3D metamorphism models and (2) images to be acquired by X-ray microtomography in experiments performed under experimentally controlled conditions. In detail, the main technical and scientific objectives are: -Couple purely thermodynamics and mechanical effects to model the morphological changes of the microstructure during equi-temperature metamorphism. Simulations based on the Discrete Element Method (DEM) will be coupled to existing thermodynamics models in order to properly account for densification effects. -Develop and evaluate models for temperature Gradient (TG) metamorphism, which is characterized by important faceting effects. The works will first consider simplified configurations of known crystalline orientations. Then, models will be applied to complete snow samples. - Monitor wet snow metamorphism under X-ray tomography, which is a more exploratory task. -Develop and apply up-to-date numerical homogenization models to compute snow transfer, mechanical and optical properties on the base of micro-tomography images and outputs of micro-scale metamorphism models. Systematic results obtained from series of microstructures will provide accurate data for the development of macroscopic snowpack models. After validation, the resulting models will provide simulating tools that are inaccessible today, and awaited by the various scientific communities working on snow from the micro to the macro scales. To tackle these multidisciplinary issues, the project team gathers scientists originating from diverse but connected scientific communities (applied mathematics, mechanics, material sciences, environmental engineering). Active collaboration between the partners will systematically be promoted, and additional external expertise will also be sought when required.