No abstract

We present a new methodology that is able to concurrently resolve free surface wavefield, bottom boundary layer, and sediment transport processes throughout the entire water column. The new model, called SedWaveFoam, is developed by integrating an Eulerian two-phase model for sediment transport, SedFoam, and a surface wave solver, InterFoam/waves2Foam, in the OpenFOAM framework. SedWaveFoam is validated with a large wave flume data for sheet flow driven by monochromatic nonbreaking waves. To isolate the effect of free surface, SedWaveFoam results are contrasted with one-dimensional-vertical SedFoam results, where the latter represents the oscillating water tunnel condition. Results demonstrate that wave-averaged total sediment fluxes in both models are onshore-directed; however, this onshore transport is significantly enhanced under surface waves. Onshore-directed near-bed sediment flux is driven by a small mean current mainly associated with velocity skewness. More importantly, progressive wave streaming drives onshore transport mostly in suspended load region due to an intrawave sediment flux. Further analysis suggests that the enhanced onshore transport in suspended load is due to a "wave-stirring" mechanism, which signifies a nonlinear interaction between waves, streaming currents, and sediment suspension. We present some preliminary efforts to parameterize the wave-stirring mechanism in intrawave sediment transport formulations.While a significant progress has been made in understanding wave-driven sediment transport based on OWT data and 1DV bottom boundary layer models, main differences exist between these idealized apparatus/domains and realistic WBBL under surface waves. The oscillatory bottom boundary layer generated in OWT is only approximately similar to the WBBL under surface waves mainly because of its homogeneous flow field in the direction of wave propagation. Considering a small amplitude (linear) progressive surface wave train, a slight inhomogeneity exists in the direction of wave propagation, which results in an onshore-directed streaming current in the wave-averaged formulation (Longuet-Higgins, 1953). In this KIM ET AL. 4693

No abstract

No abstract

Turbulence characteristics in the swash zone are investigated using a 3‐D large eddy simulation model. The numerical model is implemented based on OpenFOAM which solves the filtered Navier‐Stokes equations for two immiscible fluids with a standard Smagorinsky subgrid‐scale closure. The numerical model is validated with laboratory data for swash flow driven by a dam‐break apparatus. The model results demonstrate that the main characteristics of turbulence in the swash zone are different from those in the surf zone, which are mainly induced by surface wave breaking. During uprush phase, bore‐generated turbulence has 2‐D turbulence characteristics because of limited water depth. Near‐bed‐generated turbulence is mainly observed during backwash. Turbulence production and turbulent dissipation rate estimated from the model results indicate an imbalance, possibly due to advection at swash front and large roughness used. Touching down of turbulent coherent structure (TCS) is observed during uprush, which drives intense bed shear stress. During the backwash, interaction between TCS and bed is less clear. However, finger‐like patterns in the spatial extent of bed shear stress and vertical components of vorticity are predicted during the backwash. The location of the strongest finger patterns in the vertical direction is collocated with that of maximum turbulence production. These finger patterns are likely caused by boundary layer instabilities injected vertically from the bed.