Experimental velocities and accelerations in very steep wave events in deep water

The entire experimental velocity and acceleration fields in the six steepest cases of a campaign of totally 122 large wave events in deep water are documented. From observations in these six waves, totally 36000 experimental velocity vectors are put on non-dimensional form using a suitable reference velocity defined by , where k and ϵ are obtained as follows: from the wave record at a fixed position the local trough-to-trough period, TTT and the maximal elevation of the event above mean sea level, ζm are defined. The local wavenumber, k and the wave slope, ϵ are evaluated from ω2/(gk)=1+ϵ2 and where ω=2π/TTT and . The wave slope for the large wave events in laboratory shown here is in the range 0.40–0.46 and is realized for focussing wave events. The procedure employed to measurements in the field estimates ϵ≃0.39 for the Draupner wave and ϵ≃0.38 for the Camille wave. The horizontal velocities obtained in the laboratory campaign are always less than the wave speed. The velocity vector has magnitude comparable to the wave speed in the strongest case and is manifested in the jet that develops at the front face of the breaking waves. The non-breaking waves exhibit a maximal horizontal acceleration up to about 0.7g in the front face of the wave at vertical level about half way to the crest. The overturning events exhibit horizontal accelerations up to 1.1g and vertical accelerations up to 1.5g in the front face of the wave, at the base below the overturning jet. The wave profile and the velocity and acceleration fields exhibit strong front/back asymmetry. The acceleration vectors extracted in close vicinity of the wave contour plus the acceleration of gravity along the (positive) vertical give vectors that are close to the normal of the surface contour.