Improvements and enhancements of mps in free surface flow simulation.

Abstract

The grid-based Eulerian methods have dominated the CFD (Computational Fluid Dynamics) for decades due to its simplicity. The grids not only used for discretize the simulation domain but also used for the computation, however, due to the inherent disadvantages of the grid-based Eulerian method, the free surface flow cannot be simulated successfully without special numerical techniques. Recently, another numerical approach has been developed for hydraulic simulation, namely, the particlebased Lagrangian approach. In this approach, the domain discretization as well as the simulation procedure differs from traditional Eulerian approach. gridless methods are typical Lagrangian based method, the basic simulation elements used to discretize the simulation domain become particles rather than grids in gridless method, which leads the capability of the gridless method in simulating free surface flow. During recent decades, the gridless methods become a robust tool in simulating hydraulic engineering problems, however, since the gridless particle-based methods are young, improvements and enhancements on the particle-based methods are expected, which will extend and strengthen the particle-based Lagrangian method in hydraulic simulation. This study is mainly focused on one of the most famous gridless method, namely the MPS (Moving Particle Semi-implicit) method. This particle-based method is first developed by Koshizuka in 1995 and has been utilized in some of simple hydraulic problems previously. In this study, improvements and enhancements on MPS method are discussed and applied. The MPS method, with various numerical techniques, has been successfully used for open channel flow simulation, porous medium flow simulation and multiphase flow simulation in this study. The efficiency, accuracy and stability of MPS method has been greatly improved and the versatility of the MPS method is then proved and extended. Different kinds of fluid flows have been simulated and discussed in this study. The quantitative comparison for dam break flow has made in this study to show the accuracy of MPS method in solving hydraulic problems. While in open channel flow simulation, the roughness height has first been considered in MPS method and a corresponding parameter is defined in MPS method to represent the roughness effects. For porous medium flow simulation, additional porous flow terms are successfully applied in MPS method to show the behaviours of porous medium flow. Finally, for air-water multiphase flow simulation, the surface tension has been included in MPS method and the density differentials between air and water phase has been overcome in MPS simulation. For water-sediment multiphase flow simulation, a rheology model and a viscosity smoothening term are executed in MPS method. All the simulation cases in this study show promising simulation results and the capacity of MPS method in hydraulic simulation has been confirmed.