Extension de la DEM aux granulaires immergés pour l’étude des suspensions denses
Membres du jury
Mr Frédéric DUFOUR: Professeur à 3SR INP Grenoble, Président
Mr Jean Noël ROUX Ingénieur des Ponts, chercheur (HDR) à Navier , Rapporteur
Mme Pascale AUSSILLOUS Maître de conférence (HDR) à Polytech Marseille , Rapporteur
Mme Élisabeth LEMAIRE Directeur de recherche, Examinateur
Mr Bruno CHAREYRE Maître de conférence (HDR) à 3SR INP Grenoble, Directeur de thèse
Mr Julien CHAUCHAT Maître de conférence au LEGI INP Grenoble, Co-Encadrant de thèse
Abstract
A numerical model is used to simulate rheometer experiments at constant normal stress on dense suspensions of spheres. The complete model includes sphere-sphere contacts using a soft contact approach, short range hydro-dynamic interactions defined by frame-invariant expressions of forces and torques in the lubrication approximation, and drag forces resulting from the poromechanical coupling computed with the DEM-PFV technique. Series of simulations in which some of the coupling terms are neglected, are also performed to evaluate the impact of some approximations which are classical in the literature. It is found that the shear component of short range interactions plays a significant role in the magnitude of the bulk stress and it has a critical effect on the evolution of solid fraction. The effect of the poromechanical coupling is visible in the transient regime. The bulk shear stress is decomposed into contact stress and hydrodynamic stress terms whose dependency on the dimensionless shear rate I v are examined. Both contributions are increasing functions of I v . Statistics of microstructural variables are computed and highlight a complex interplay between contacts and hydrodynamic interactions. Finally, the dependance of the behavior of submarine avalanches function of the fluid viscosity η and of the angle θ of the material relative to the horizontal is studied. Results are in a good agreement with the phenomenological laws found experimentally.
Keywords
discrete element method, finite volume, poromechanical coupling, lubrication, dense suspensions, rheology.