An experiment at sea on the reflection of the wind waves

In 1991, in the sea of Reggio Calabria to confirm the forecasts of the Boccotti's theory related to the waves subjected to reflection and diffraction, a small vertical breakwater was built (12 m long and 2.1 m high on a bottom depth of 1.5 m). In front of the wall, 30 gauges were located: 12 pressure transducers were fixed to the wall. Two beams, the one perpendicular and the other parallel to the wall supported 18 pressure transducers. The transducers were all placed at the same depth: 0.60 m under the M.W.L.. The beams, which carried out the transducers, were realized in a space frame structure to obtain maximum rigidity with the minimum section, and were sustained by the same telescopic piles used during the 1990 experiment. An ultrasonic probe was located in the progressive wave field and all the instruments were connected to the electronic station by submarine wires. The quasi-determinism theory foresees that an exceptionally high wave on the wall is formed because a well defined three-dimensional group hit the wall at the apex of its development stage. The exceptionally high wave is the one at the centre of the group, which doubles its height because of the reflection. Besides, the theory foresees that an exceptionally high wave, in the water sheet in front of the breakwater is formed as the result of a frontal collision of two groups: the one approaching the wall and the other leaving the wall, after the reflection. The experiment achieved the objective and produced a net confirmation of the two characteristics ways of formation of the high waves on the wall and in front it.Then, the experiment confirmed another prediction of the quasi-determinism theory: in the wind waves, at just some wavelength from the breakwater, nodes and antinodes disappear completely. Finally, the experiment revealed also a characteristic pressure-fall under the crests of the highest waves at the wall. The phenomenom was related to high water jets delected at the centers of the wave fronts.