Investigation of debris flow-structure interaction using CFD, DEM and coupled method

Abstract

A debris flow is a rapid moving mass of fluid-sediments mixtures that travels down a slope under the influence of gravity. Both solid and fluid phases vitally influence the debris flow dynamics. Due to high sediment concentration and mobility characteristics, debris flow can be extremely destructive, which greatly threatens people’s life and property safety. In this study, the behavior of fluid phase is resolved by solving the Reynolds Averaged Navier-Stokes equation in CFD (Computational Fluid Dynamics), with the Volume of Fraction (VOF) method to solve the water part in fluid phase, while the DEM (Discrete Element Method) is used to simulate solid materials by particle contact model. The coupled CFD-DEM simulation accounts for various solid and fluid interaction forces in debris flow, which consist of the buoyancy force, drag force and virtual mass force and so on. Through some validations and simulations, it is demonstrated that the coupled CFD-DEM model using the VOF method is an efficient and reliable numerical tool to simulate the three-phase air-water-particle system and study the fluid-particle interaction of the debris flow. The Bonded Particle Model (BPM) in DEM is implemented to model the structure, so that the failure pattern and damage of structures from debris flow impact can be studied, which help to enhance our understanding on debris flow-structure interaction mechanism. A parallel bond is established between two particles to model the mechanical behaviour of the brittle cement. Validation case, including the bending of a cantilever beam, has been conducted to verify that the bonded particle model can be used to reproduce macroscopic characteristics of the cemented material. The comparison case of the bonded particles and unbonded particles settling from the air into water, has been conducted to study the influence of the flow field on different types of particles column with or without bonding, which also validates the feasibility of implementing Bonded Particle Model in the coupled CFD-DEM method. The rheological behaviour of a debris flow and the three-dimensional topography of its path greatly influence the debris flow mobility and impact force on structures. Incorporation of topography plays a crucial role in analysing the historical landslide events or predicting the scope of influence of the possible disaster.

Date of Award	2018
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology