26/04/2018 - Yeulwoo Kim
Wave-driven sediment transport is one of the key drivers of beach morphodyanmics. However, a comprehensive understanding of that has not been achieved due to many inter-conneted complex mechanisms such as free surface effect, boundary layer process, and wave breaking induced turbulence. Thus, a new methodology that is able to concurrently resolve free surface wave field, bottom boundary layer and sediment transport processes throughout the entire water column is essential. Recently, SedWaveFoam was developed for this purpose by merging capabilities from an Eulerian two-phase flow model, SedFoam (Cheng et al., 2017, Coast. Eng.) and a volume-of-fluid solver, interFoam/waves2Foam (Jacobsen et al., 2011, Coast. Eng.) in the OpenFOAM framework. SedWaveFoam treats the air and water phases as two immiscible fluids and tracks the evolution of the air-water interface, while dealing with the dispersed sediment particles as a third continuum. The full profiles of flow fields and sediment transport are computed using Reynolds-averaged Eulerian two-phase flow equations with closures of inter-granular stresses and a k-ε turbulence model. SedWaveFoam was recently validated with the large wave flume experiment data of Dohmen-Janssen and Hanes (2002, JGR) for sheet flow under non-breaking monochromic waves and revealed the effects of progressive wave streaming and wave-stirring mechanisms (Kim et al., 2018, JGR, submitted). SedWaveFoam is further applied to investigate the sediment transport over complex bathymetry under more extreme wave condition such as breaking waves and compared with the measured data from the sandBAR SEDiment transport experiment (BARSED ; Mieras et al., 2017, JGR). A 2-dimensional numerical flume is contructed that has exactly the same length and depth as in the physical experiment, discretized using an unstructured mesh with O(1 mm) near the sandbar bed and O(10 mm) around the free-surface. Overall, the modeled hydrodynamics (e.g., free-surface elevation and velocity) agree well with the measured data with Normalized Root Mean Square Error (NRMSE) less than 2%. The model is also able to predict sediment concentration profiles at the sandbar crest with NRMSE < 1.2% through the wave cycle. This new modeling approach allows the inclusion of physical processes like wave breaking induced turbulence and boundary layer streaming in sediment transport and it will likely improve sediment transport predictions under highly non-linear and skewed-aymmetric breaking waves.