On segregation in bidisperse granular flows

Abstract

Every year, thousands of people die due to landslides, avalanches and other natural disasters in which separate particles play an important role. For accurate zonation and risk assessment, efficient models are needed that not only take into account the basal topo-graphy, but also the properties of these particles (snow, rock, sand, etc.), such as size- and shape-distribution. The conglomoration of particles is called a granular material, and the flow of a granular material is a granular flow. When a granular material is composed of multiple components that differ in e.g. size, density or shape, the mixture usually segregates into separate phases when sheared or shaken. For example in a size-bidisperse flow over an inclined plane, which contains large and small particles, the larger particles tend to the free surface, while the small particles tend to the base. Both the cause of segregation and the phenomenological aspects are active areas of research. This thesis looks at the latter; it aims to develop efficient and accurate models of granular flows, in particular of bidisperse granular flows, which consist of two types of particles. This thesis starts with developing an efficient model monodisperse granular flows through a contraction, which is validated with a more complex model. This is followed by a model for size-bidisperse flows over an uniform channel, which shows the bulbous head as emergent segregation structure. Then a new technique for mapping discrete particle data to continuum fields is presented, and finally the segregation behaviour of shape-bidisperse particles with different elongations is studied.