Discrete-element method simulations:: from micro to macro scales

Many liquid systems encountered in environmental science are often complex mixtures of many components which place severe demands on traditional computational modelling techniques. A meso scale description is required to account adequately for their flow behaviour on the meso and macro scales. Traditional techniques of computational fluid dynamics and molecular simulation are not well suited to tackling these systems, and researchers are increasingly turning to a range of relatively new computational techniques that offer the prospect of addressing the factors relevant to multicomponent multiphase liquids on length- and time-scales between the molecular level and the macro scale. In this category, we discuss the off-lattice techniques of 'smooth particle hydrodynamics' (SPH) and 'dissipative particle dynamics' (DPD), and the grid-based techniques of 'lattice gas' and 'lattice Boltzmann' (LB). We highlight the main conceptual and technical features underpinning these methods, their strengths and weaknesses, and provide a few examples of the applications of these techniques that illustrate their utility.