|Wave-current interaction in the presence of a three-dimensional bathymetry: Deep water wave focusing in opposing current conditions |
(Article) Publié: Physics Of Fluids, vol. 26 p.096601 (2014)
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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-diffractionmodel assuming a depth-averaged current. If the model qualitatively predicts thewave amplification in the centerline of the basin, discrepancies are observed in thevicinity of the depth changes. The observed mean current vertical profile shape isthen supposed to play a significant role in the wave focusing, especially near thesteep slopes down-stream the mounds. In addition, the waves are found to modifysubstantially both horizontal and vertical current fields.