Prototype-scale simulation of key wave parameters and force induced by black tsunamis

Abstract

Black tsunamis, characterized by high concentrations of suspended fine sediments, pose serious threats to marine infrastructure, particularly in enclosed ports and bay areas. This study applies FS3M, a multiphase flow model that incorporates sediment-induced variations in density and viscosity, to numerically investigate black-tsunami impacts. The model is first validated against small-scale flume experiments with different sediment concentrations, showing good agreement in water level, wave pressure, and wave force. Prototype-scale 2D and 3D simulations are then conducted. In the 2D cases, suspended sediment enhances viscous damping under non-breaking conditions, reducing inundation depth and flow velocity. Under breaking conditions, added-mass effects near the quay wall dominate, intensifying the initial surge and inducing vertical stratification. Based on these findings, 3D simulations place structures at three apron positions to examine spatial variability. For non-breaking tsunamis (H = 6–8 m), sediment consistently attenuates horizontal wave forces, indicating that clear-water simulations provide conservative estimates. In contrast, some breaking-wave cases (H = 10 m) exhibit force amplification (ratios 1.02–1.06). These results demonstrate that relying solely on water level may underestimate forces under energetic, sediment-laden conditions, highlighting the need to consider dynamic indicators and emphasizing the importance of including sediment effects in tsunami impact assessments.