Wave Kinematics and Surface Parameters of Steep Waves Traveling on Sheared Currents

Abstract

Measurements have been made of the velocity field and wave parameters for large waves on a moderately sheared current in a wave flume. Comparisons are made between the velocity fields measured with particle image velocimetry (PIV), the predictions due to irrotational wave theory combined with current stretching, and a fully nonlinear constant vorticity model. The stretching theory is found to be in good agreement with the constant vorticity model. The experimentally measured velocity profiles are well predicted by the models, except in the steepest cases (above 60 steepness), where the crest velocities are overpredicted and the trough velocities are underpredicted. Values of the equivalent current derived for the surface parameters are compared with near surface current weighting methods. It is found that the surface current value is closer to the equivalent current than any of the weighting methods.