Wave-current interaction in the presence of a three-dimensional bathymetry: Deep water wave focusing in opposing current conditions
Résumé
Large scale experiments were carried out in the Ocean Engineering Basin FIRST, France. A tri-dimensional bathymetry consisting of two symmetrical submerged mounds was displayed on the flat bed on both sides of the basin. Regular waves of frequency corresponding to deep water conditions above the bathymetry were generated in opposing current conditions. A strong tri-dimensional behaviour is observed for thewave amplitude, leading to a strong focusing (up to twice the incident amplitude) of the wave energy towards the central deeper zone. This amplification cannot be ascribed to the increase of the current intensity in the main wave direction, nor to a current gradient normally to the wave direction. A wave phase gradient, normal to its main direction, is observed up-wave (or downstream) the mounds. This phase lag depends on the wave amplitude, it is the higher for the moderate amplitude case. The experimental data are compared with calculations of a refraction-diffraction
model assuming a depth-averaged current. If the model qualitatively predicts the
wave amplification in the centerline of the basin, discrepancies are observed in the
vicinity of the depth changes. The observed mean current vertical profile shape is
then supposed to play a significant role in the wave focusing, especially near the
steep slopes down-stream the mounds. In addition, the waves are found to modify
substantially both horizontal and vertical current fields.