A CFD-DEM-FEM framework for sediment-laden free-surface flow interacting with flexible structures

Coastal and offshore protective structures are often loaded by free-surface flows that carry sediment. This study develops a three-phase numerical framework that couples Computational Fluid Dynamics (CFD), the Discrete Element Method (DEM), and the Finite Element Method (FEM) for fluid-particle-structure interaction. The framework combines a semi-resolved CFD-DEM method that is independent of particle shape and mesh size, an Arbitrary Lagrangian-Eulerian (ALE) formulation with Interface Quasi-Newton with Inverse Least Squares (IQN-ILS) and Radial Basis Function (RBF) interpolation for fluid-structure coupling, and an adaptive wall-update algorithm that reduces non-physical force oscillations at the FEM-DEM interface. Non-spherical particle clusters are represented with a bonded multi-sphere model. After benchmark validation, the model is applied to seepage-induced erosion beneath a flexible barrier and sediment-laden dam-break impact on a flexible baffle. Cubic particles produce smoother and lower collision forces because of interlocking, whereas spherical particles generate high-frequency impacts. As structural stiffness increases, the dominant load changes from particle impact to hydrodynamic pressure. The results show that the CFD-DEM-FEM framework can capture particle-shape effects, sediment shielding, and stiffness-dependent loading transitions in sediment-laden free-surface flows.