| Summary: | 碩士 === 國立交通大學 === 土木工程系所 === 101 === This study aims to investigate the behavior of migration and deposition for debris flow using two-phase flow analysis of fluid dynamics. This work made use of “COMSOL Multiphysics” (herein referred to as "COMSOL") as the numerical simulation tool to simulate fluid behavior of two-phase flow. The rheological models of debris flow are assumed to be Non-Newtonian fluid, including yield shear stress, viscous stress, dispersive shear stress from particles collision, and turbulent stress from bed roughness, and so on.
Reviewing rheological models and parameters for debris flows from previous studies, debris flow rheological properties vary with the particle size distribution, mineral properties, debris flow’s sediment concentration, and other physical quantities. It should be reasonable to consider the debris flow rheological model and its corresponding rheological properties together. This study deliberately validates the ranges of parameters which are collected in order, and view them as basis for simulation.
This study regards COMSOL as an analysis platform to build debris flow migration model and to design debris flow rheological model as well. With the rheological model for mudflow, this study uses effective viscosity from the effective Bingham rheological behavior so that the Navior-Stokes equation originally simulating Newtonian fluid is able to simulate rheological behavior of Bingham fluid. For rheological model of stony debris flow, considering that particles collision force and turbulent force are square proportional to shear rate, this study adds particles collision force and turbulent force as volume forces to the Navior-Stokes equation originally simulating Newtonian fluid. Assuming that the yield shear stress is constant, viscous flow is proportional to the velocity flow gradient; the shear stress due to particle collision is proportional to the square of flow rate of gradient. When the shear stress is neglected, this rheological model is reduced to the Bingham model.
This study evaluates whether the behavior of the migration and deposition of debris flow is reasonably simulated. The major role of the Level Set method is to distinguish the interface between debris flow and air. However, the problem of poor mass conservation for debris flow appears. It appears the mesh size and the interface thickness of two phase flow have an influence on the quantity of poor mass conservation.
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