| New parameterizations of the near bed dynamics over a mobile rippled sediment bed subjected to free-surface gravity waves were computed from a comprehensive array of observations collected with Particle Image Velocimetry. Analysis techniques included a quasi-steady space-varying approach and space-averaging methods using the time-varying and time-invariant form of the Reynolds Averaged Navier Stokes equations. Fitting a logarithmic layer model to quasi-steady velocity profiles appropriately capture the intra-ripple flow characteristics at most locations along the rippled bed, but generalizing to a single position does not accurately represent the dynamics over the entire ripple. To this end, a space-averaging technique was implemented on the observations. The technique allows for a comprehensive stress partitioning scheme and direct estimates of the bedform-induced pressure. In both, its time-varying and time-invariant form, the space-averaging technique provides a description of the momentum transfer mechanisms responsible for ripple mobilization. This data reduction technique was also employed to obtain new estimates of friction factors, drag coefficients, and eddy viscosities, all of which are provided in terms of the ripple relative roughness. |
