EarthFlow: Mixed (fluid+solid) flows
Talk in relation with the EarthFlow project, but addressed to a broad audience, by Marcin Dabrowski (PGP, UiO).
FEM simulation of rigid inclusions in a linear viscous matrix under shear. The stress trajectories are shown and the second invariant of stress tensor is color-coded.
Flows in the Earth's interior are often heterogeneous, with solid constituents surrounded by fluid. At low fractions, the solid phase can be fully immersed in the fluid forming a suspension. Although without developing direct contacts, the interactions among inclusions can be significant and lead to mixing phenomena such as shear-induced self-diffusion. The overall viscosity is, to a large degree, determined by the fluid properties. Increasing solid volume fractions towards the jamming threshold leads to the formation of an extensive network of contacting particles. Granular materials are an example such as the broken debris generated along earthquake faults or in rockslides. The effective mechanical behavior is dominated by fracturing of grains and frictional interactions at grain contacts leading to strongly non-linear rheological behavior, largely independent of the interstitial fluid. However, many natural systems have intermediate fraction values and exhibit a spectrum of rheological behavior, including concomitant ductile and brittle mechanisms. It is largely unknown how these mechanisms combine and whether shear localization, which is typical for granular materials, could occur in such transitional systems. Direct numerical simulations of such processes are quite challenging due to a large number of particles, direct contacts developing among them, and unprecedentedly long time series required for reliable statistical analysis of particle dynamics. In the Mixed (fluid+solid) flow theme of the EarthFlow project, we aim to study the transitional regime between suspension and granular flows.