Abstract
A new three-dimensional nearshore hydrodynamic model system is developed based on the unstructured-grid version of the third generation spectral wave model SWAN (Un-SWAN) coupled with the three-dimensional ocean circulation model FVCOM to enable the full representation of the wave-current interaction in the nearshore region. A new wave–current coupling scheme is developed by adopting the vortex-force (VF) scheme to represent the wave–current interaction. The GLS turbulence model is also modified to better reproduce wave-breaking enhanced turbulence, together with a roller transport model to account for the effect of surface wave roller. This new model system is validated first against a theoretical case of obliquely incident waves on a planar beach, and then applied to three test cases: a laboratory scale experiment of normal waves on a beach with a fixed breaker bar, a field experiment of oblique incident waves on a natural, sandy barred beach (Duck’94 experiment), and a laboratory study of normal-incident waves propagating around a shore-parallel breakwater. Overall, the model predictions agree well with the available measurements in these tests, illustrating the robustness and efficiency of the present model for very different spatial scales and hydrodynamic conditions. Sensitivity tests indicate the importance of roller effects and wave energy dissipation on the mean flow (undertow) profile over the depth. These tests further suggest to adopt a spatially varying value for roller effects across the beach. In addition, the parameter values in the GLS turbulence model should be spatially inhomogeneous, which leads to better prediction of the turbulent kinetic energy and an improved prediction of the undertow velocity profile.
Highlights
The interaction of wind-generated surface gravity waves with slowly varying ocean currents in shallow coastal areas can create rents on the waves are the current-induced refraction and Doppler frequency shift (Kumar et al, 2012; hereafter K12)
A new three-dimensional hydrodynamic model has been developed in the present study by coupling the third generation spectral wave model SWAN with the oceanographic model FVCOM
A new wave-current coupling scheme is developed, including a Generic Length Scale (GLS) turbulence model to reproduce the wavebreaking enhanced turbulence, as well as a roller transport model to account for wave breaking under influence of the surface roller
Summary
The interaction of wind-generated surface gravity waves with slowly varying ocean currents in shallow coastal areas can create rents on the waves are the current-induced refraction and Doppler frequency shift (Kumar et al, 2012; hereafter K12). The VF formalism has been widely used to represent the additional terms corresponding to WEC in the momentum equations It splits the wave-averaged effects into gradients of Bernoulli head and a vortex force and has a primary advantage of explicitly including a type of wave–current interaction that few if any available wave models properly incorporate to allow its complete expression in the radiation stress (Uchiyama et al, 2010, hereinafter U10; Newberger and Allen 2007a, 2007b, hereafter NA07; McWilliams et al 2004, hereinafter MRL04). The K-profile parameterization (KPP) is found difficult to represent accurately the mixing in the bottom boundary layer and in nearshore regions (Durski et al, 2004) This is due to the fact that to develop and verify a turbulence scheme’s suitability in modeling wave breaking, much detailed measurements in laboratory controlled conditions in both flow hydrodynamics and turbulence characteristics, as well as free surface variations are required.
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