From particle simulations towards continuum theory and applications

The dynamic behavior of particulate and granular matter – like sand, powder, suspended particles or molecules, often with a wide distribution of particle sizes – is of considerable interest in a wide range of industries and research disciplines since they can behave both solid-like and fluid-like. The related mechanisms/processes in particle systems are active at multiple scales (from nano-meters to meters), and finding the reasons for, e.g., the reasons for natural disasters like avalanches or plant problems like silo-failure, is an essential challenge for both academia and industry.

            In order to understand the fundamental micro-mechanics one can use particle simulation methods, where often the fluid between the particles is important too. However, large-scale applications (due to their enormous particle numbers) have to be addressed by coarse-grained models or by continuum theory. In order to bridge the gap between the scales, so-called micro-macro transition methods are necessary, which translate particle positions, velocities and forces into density-, stress-, and strain-fields. These macroscopic quantities must be compatible with the conservation equations for mass and momentum of continuum theory. Furthermore, non-classical fields are needed to describe the micro-structure (fabric, force-chains) or the statistical fluctuations, e.g. of the kinetic energy, before one can reach the ultimate goal of solving application problems.

Examples of multi-scale simulations, involving particle- and continuum-methods, are flows of particles/fluids in narrow channels/pores, dosing of cohesive fine powders in vending machines, avalanche flows on inclined slopes, segregation, rheology testing in ring-shear cells, as well as the study of non-linear elasto-plastic material mechanics related to the failure of cohesive, frictional solids.

Prof. Stefan Luding studied physics at Bayreuth, Germany (reactions on complex and fractal geometries). He did his PhD on the simulations of dry granular materials in the group of Prof. A. Blumen in Freiburg, Germany and spent his post-doctorate time in Paris IV, Jussieu, with E. Clement and J. Duran, before he joined the Computational Physics group in Stuttgart, Germny, with Prof. Herrmann in 1995, where he achieved his habilitation in 1998.

In 2001, he moved to DelftChemTech at the TU Delft, Netherlands, as Assoc. Prof. Particle Technology. Since 2007 he chairs the group Multiscale Mechanics (MSM) at the Faculty of Engineering Technology and MESA+ at the University of Twente, Netherlands.

His major research expertise is on granular matter, non-Newtonian flow rheology, non-linear solids, particle interactions, cohesive powders, asphalt, composites, bio-/micro-fluid systems, self-healing materials and most of all on micro-macro transition methods.

Among many other tasks and services for the community, he is since 1998 Managing Editor in Chief of the journal Granular Matter as well as, since 2005, president of AEMMG organizing the Powders and Grains conference series with the next event taking place in Buenos Aires, Argentina, July, 2021.