Abstract: A coupled computational fluid dynamics (CFD) and discrete element method (DEM) model is established to capture the fluid-particle interactions in submarine landslide. The model is validated with experimental data of granular collapse in the literatures. Underwater granular collapse, as a paradigm of submarine landslide, is simulated with various initial aspect ratios, in detailed comparison with aerial granular collapse. The results show that CFD-DEM can well capture the key processes of submarine landslide, including its collapse, propagation, and deposition. Complicated interactions between water and grains are observed, such as the formation of vortex in water when the granular flow transits from vertical falling to lateral spreading. When the initial aspect ratio is high, the vertex in water can significantly modify the surface morphology of the final deposit. Compared to dry granular collapse, the underwater landslide generally leads to a shorter runout distance and thicker deposit; the loose materials on the surface are easily affected by the water flow.

Key words: computational fluid dynamics (CFD), discrete element method (DEM), coupling, submarine landslide