Projet ANR-06-BLAN-0414 – PLANETEROS : Numerical modeling of the static/flowing transition in a mixture model: application to debris flows on Earth and on Mars
Programme : Programme blanc (BLANC) 2006
Année de financement : 2006
Coordinateur du projet : CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ILE-DE-FRANCE SECTEUR PARIS B (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ILE-DE-FRANCE SECTEUR PARIS B)
Partenaires : Centre national de la recherche scientifique; Centre national de la recherche scientifique; Centre national de la recherche scientifique; Institut de physique du globe
Montant : 250000.0 euros
Date de début : 2006
Durée : 36 mois
Résumé : 1. Scientific background and objectives  Numerical modeling of gravitational flows such as debris flows or landslides offers a powerful tool for investigating geomorphologic processes on Earth and other telluric planets and assessing risks related to such natural hazards. Numerical, mathematical, physical and geophysical studies have led to the development of depth-averaged continuum models based on the thin layer approximation. Their predictive power is however questionable. Indeed, these models generally do not take into account two major processes: the existence of flow and no flow zones within the granular mass (static/flowing transition) and the interaction between a solid (grains) and a fluid (water) phase. Major progress in the theoretical study of granular materials in terms of physics and mechanics has laid the groundwork for a new generation of models capable of taking into account these fundamental processes observed in the field. Two new approaches consist once in describing explicitly the static/flowing transition through an order parameter introduced in continuum models and second in deriving 3D numerical model based on consistent constitutive equations allowing to test and to constrain thin layer models. New two-fluid models have been recently developed, containing mass and momentum equations for both the fluid and solid phase, thus providing equations for the velocities of the two phases and for porosity. The extensive accurate dataset on deposit morphology obtained by modern satellite imagery systems on Earth and on Mars now makes it possible to validate such models.  The main objective of this project is to improve the understanding of avalanche flows and their modelling at the field scale by developing mathematical, mechanical, numerical and applied field approaches in a complementary manner. The aim is to provide new insight in the static/flowing transition and fluid/solid interactions in granular flows through comparison of the simulations with laboratory experiments and application to the study of granular flows on Earth and on Mars using field and satellite data.  2. Description of project, methodology  The methodology will consist in development and use of efficient numerical models appropriate to describe the static/flowing transition and the solid/fluid mixture of the flow over a complex topography. The static/flowing transition will be investigated using two complementary approaches. In the first approach, an equation for the evolution of the static/flowing interface will be derived from the order parameter theory, linked to the solid-like contacts. The originality of this new macroscopic formulation lies in its relation with the mesoscopic scale. The second approach makes use of consistent viscoplastic constitutive models to describe 3D behavior of granular flows. The numerical results obtained with the new thin layer model will be compared with simulations based on the 3D viscoplastic model and a discrete element model. We shall compare the thin layer and visco-plastic numerical models with four experimental systems: 3D surface flows leading to triangular tracks, the collapse of a granular mass on a horizontal plane, self-channelling flows with levee formation and erosion/deposition by successive avalanches. Numerical schemes for the solution of the model equations including mixture flow and static/flowing transition will be studied in the framework of finite volume well-balanced schemes for hyperbolic systems with sources suitable to solve highly non linear systems. Numerical results will be compared to experiments involving mixture flow to assess the model reliability and efficiency in describing solid and fluid phase interaction. Finally, the thin layer model will be applied to simulate avalanches observed on Earth and on Mars. Field studies in cold regions on Earth and satellite data acquisition on Mars from new imagery of the HiRise instrument onboard Mars Reconnaissance Orbiter will be perfor