Simulation of debris-flow initiation and erosion process by a multi-phase accurate particle method.

Takaaki Abe, Takeshi Fujinami, Jungo Funaki

Wednesday 1 july 2015

11:45 - 12:00h at Oceania Foyer (level 0)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 9H. Water resources - Catchment

In this study, a modified particle method for modeling debris flows is proposed based on a constitutive equation considering granular inter-particle collisional stress. The calculation method we mainly use is based on the two-phase Moving Particle Semi-implicit (MPS) method. The MPS method is originally proposed by Koshizuka et al. (1996) for calculation of incompressible viscous fluid flows with free surfaces. There have been several attempts to develop two-phase flow schemes of the MPS method for simulating hydraulic problems such as entrapment of bubbles, diffusion process of fine sands in water, and river embankment erosion. In spite of being a flexible tool for numerically simulating these complex/abrupt behaviors of multiphase flows, the original two-phase MPS method is applicable only to Newtonian fluid flows. A modification is necessary in order to calculate highly concentrated granular flows like debris-flows which usually exhibit dilatant properties. In this study, the granular inter-particle stress term derived by Takahashi et al. (1997) is introduced to the momentum equations of the two-phase MPS method. The proposed method is applied to the simulation of flume experiments of debris-flows conducted by Hirano et al. (1992). The developed method succeeded in reproducing erosion and initiation process of the debris-flow. Then a quantitative comparison is made between the velocity distributions and the experimental results for granular flow on movable bed. Velocity profiles obtained by the proposed MPS scheme are similar to those measured by Hirano et al. (1992).