Christos Varsakelis's PhD Thesis

Granular materials, defined as large conglomerates of discrete particles, are the second most employed material in industry and agriculture, the first one being water. These conglomerates are typically immersed in an interstitial fluid, thus forming a heterogeneous, two-phase mixture. Flows of such mixtures are different from flows of simple fluids in many important ways. For example, these mixtures support shear stresses at equilibrium, they compact, they tend to clog when driven through area constrictions, they can produce avalanches, etc.
In this dissertation, we are concerned with the theoretical and numerical analysis of hydrostatics and low-Mach number flows of two-phase granular mixtures. According to our approach, each phase is treated as an open thermodynamic system that interacts with the other one. First, we derive the low-Mach number equations for the mixtures of interest by generalizing the concept of low-Mach number asymptotics to multi-phase flows. Further, we develop an existence theory and a numerical method for hydrostatics of two-phase granular mixtures. Finally, we present an algorithm for the calculation of incompressible flows of granular mixtures and we employ it for the first ever numerical study of unsteady multi-dimensional shear flows for the mixtures of interest.

Jury :
Prof. Miltiadis PAPALEXANDRIS (UCL), Promoteur
Prof. Grégoire WINCKELMANS (UCL), Président
Prof. François DUPRET (UCL), Secrétaire
Prof. Jean VAN SCHAFTINGEN (UCL)
Dr Vincent DELEDICQUE (Bel V., Belgique)
Prof. Christian ROHDE (Université de Stuttgart, Allemagne)