Aspects of seabed shear stresses under long-crested and short-crested irregular waves

The wave boundary layer relates to many phenomena in coastal and offshore engineering as well as in oceanography, e.g. sediment transport, pipeline stability, etc. The wave boundary layer has been studied by itself and also in combination with the current boundary layer since the flow from waves interacting with currents represents the most common flow condition on the seabed for shallow and intermediate water depths, i.e., in coastal zones and on continental shelves. The paper will present some aspects of seabed shear stresses under long-crested and short-crested irregular waves. These aspects are studied analytically using the two-layer time-invariant eddy viscocity approach of Brevik (1981)to calculate the seabed shear stresses under sinusoidal waves. Comparisons are made with the Jonsson and Carlsen (1976)data as well as the Sumer et al. (1987) data for harmonic oscillations. The predicted to measured ratios of the wave friction coefficients for these data are in the range 0.78 to 0.96, showing that the Brevik (1981) approach is a reasonable compromise between simplicity and accuracy for harmonic oscillations. This formulation is then extended to study the seabed shear stresses under long-crested and short-crested irregular waves.