Spatial variability of the wave bottom boundary layer over movable rippled beds

摘要: Observations of the spatially dependent velocity field over movable bed forms subjected to slightly skewed and asymmetric regular wave forcing were collected. The dynamics between ripple elements is dominated by coherent vortices, characterized swirling strength, evidenced in temporal spectral characterization. Within boundary layer, energy second harmonic (3f0) amplified at slopes consistent with location expected strongest pressure gradients. First-moment second-moment statistics used address spatial variability intra-ripple hydrodynamics. Estimates displacement momentum thicknesses (?* ?mom) are smaller than suggested higher harmonics, but consistently highlight areas adverse favorable Shear stress roughness estimates inferred fitting a logarithmic model first-moment field. maximum Shields parameter was observed peak stoss slope ripples during shorter half-wave period (onshore). similar magnitude load parameterizations provided Li et al. (1997), about factor 3 larger estimates. Assessment vertical transfer horizontal derived using Reynolds decomposition suggests that stresses from law appropriately reproduce mean for longer weaker offshore period.