A Coupled PFEM-DEM Model for Fluid-Granular Flows with Free-Surface Dynamics Applied to Landslides

TL;DR

This work addresses the challenging problem of simulating fluid-granular flows with strong free-surface dynamics and large domain deformations, such as landslides generating impulse waves. It introduces a fully coupled two-way PFEM-DEM framework in a fully Lagrangian setting, where the fluid is discretized by PFEM and the granular phase by DEM with NSCD contacts; grains are projected into the fluid domain to compute void fractions and fluid-grain forces, and exact overlap calculations ensure conservative coupling. The approach is validated against dam-break and granular column collapse benchmarks and applied to the 1958 Lituya Bay landslide and tsunami, demonstrating the model's ability to capture free-surface waves and complex grain–water interactions, including wave reflection phenomena. Limitations include two-dimensionality, non-conservation of fluid volume due to the advection scheme, and remeshing-induced diffusion; future work points to 3D extension, improved volume conservation, and scalable parallel implementations for real-scale applications.

Abstract

Free surface and granular fluid mechanics problems combine the challenges of fluid dynamics with aspects of granular behaviour. This type of problem is particularly relevant in contexts such as the flow of sediments in rivers, the movement of granular soils in reservoirs, or the interactions between a fluid and granular materials in industrial processes such as silos. The numerical simulation of these phenomena is challenging because the solution depends not only on the multiple phases that strongly interact with each other, but also on the need to describe the geometric evolution of the different interfaces. This paper presents an approach to the simulation of fluid-granular phenomena involving strongly deforming free surfaces. The Discrete Element Method (DEM) is combined with the Particle Finite Element Method (PFEM) and the fluid-grain interface is treated by a two-way coupling between the two phases. The fluid-air interface is solved by a free surface model. The geometric and topological variations are therefore naturally provided by the full Lagrangian description of all phases. The approach is validated on benchmark test cases such as two-phase dam failures and then applied to a real landslide problem.

Figures (18)

• Figure 1: In this study, two types of interfaces are a source of complexity: the free-surface between fluid and air, and the solid-fluid interface.
• Figure 2: We present a fully coupled PFEM-DEM formulation for the simulation of fluid-grain flows with strong domain deformations.
• Figure 3: Illustration of the fluid-grains coupling. Grains are represented as a continuous field using an $L_2$ projection. The integral over the disc is approximated by the sum of the integrals over the elements containing the grain. The red dot represents the centroid of each overlapped sub-element. The void fraction is indicated by the colour map.
• Figure 4: A schematic of the algorithm.
• Figure 5: Chaotic free surface flows require the method to be able to track complex topological changes and to detect boundaries.