Simulations of debris flow impacting on bridge pier based on coupled CFD-DEM method

Abstract

In many recorded natural disasters, the floating debris was observed to contribute a lot to the destructive power of violent water against structures. To explore the impacting effects acting on the bridge pier from a debris flow in a tsunami disaster, a three-phase numerical model is used based on a Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) coupling method. The Navier-Stokes equations are adopted to describe the fluid behaviors with the Volume of Fluid (VOF) method to track the free surface, and a virtual dual grid porosity model is adopted to calculate the fluid porosity. The particles are computed by the Newton's laws and contact laws. The simulated results of single particle sedimentation, single particle floating in dam-break flow, and the settling of particles with different diameters agree well with the literature, which validate this model. The model was then employed to investigate the fluid flow with the floating particles colliding with the bridge pier using dam-break flow to simulate the tsunami bore. The results show the impacting load from the debris flow acting on the bridge pier is 295% larger than the impacting load from the flow without debris, and expose the impacting procedure.