Multiscale modelling of fluid-immersed granular media

In this thesis we present numerical simulation studies of fluid-immersed granular systems using models of varying scales and complexities. These techniques are used to examine the effects of an interstitial fluid on the dynamics of dense granular beds within a number of vibrated systems. After an introduction to the field of granular materials, we present the techniques used to model both the granular dynamics and the fluid flow. We introduce various multiscale techniques to couple the motion of the granular and fluid phases. An extensive comparison between these techniques is conducted for some well-known systems. The fluid-grain coupling techniques are applied to some larger systems in order to determine under what situations the approaches are most suitable. An investigation concerning three-dimensional fluid-driven convection within vertically vibrated fluid-immersed granular beds is then presented. Here we observe granular piling and determine that this is a result of fluid-driven convective cycles within the bed which may be strengthened through the presence of wall friction. Our simulations capture this convective behaviour and lead to a detailed understanding of the mechanisms behind the phenomenon. Under a wide range of conditions a system of fluid-immersed fine grains within a vibrated partitioned cell will transfer in their entirety into just one of the segments through a linking channel at the cell base. We perform an experimental and numerical study in order to understand the principle mechanisms behind the “partition instability”. We determine that the instability arises due to the fluid experiencing less resistance to its motion when flowing through the shallower granular column during vibration. A simple analytical model is developed which captures this behaviour. It is commonly known that large dense intruders may rise rapidly to the surface of a granular bed when subjected to a vertical vibrational force. We next present an experimental and numerical study to determine the principle mechanism associated when the granular bed is immersed in a fluid, the fluid-enhanced Brazil nut effect. Our key finding is that the behaviour of the intruder is sensitive to the detailed fluid and particle flow in its vicinity. An analytical approach is developed to model the rising of a dense intruder in a vibrating fluid-immersed porous bed. Finally a brief study is presented into the behaviour of a vibrated system of fluid-immersed particles held within a zero-gravity environment. We conduct simulations which are able to reproduce the behaviour of a collection of particles suspended magnetically in a vibrating fluid