Wave field behind a double-submerged breakwater

To find more desirable wave field behind a submerged breakwater in terms of wave interception, mean water level change, wave profile, and so on, and to cope with the construction cost of the submerged breakwater which increases quadratically as the water depth increases, we considered that a double-submerged breakwater, which is a pair of two small submerged breakwaters located some distance apart, might be one solution. In order to study the wave field behind the double submerged breakwaters, we conducted wave tank experiments using random waves of several significant waves. Water surface oscillation and fluid velocity at the bottom were :measured. Spatial changes of wave amplitude spectra, flow velocity spectra, mean water level change, skewness and atiltness of the wave profile of the water surface and the bottom velocity oscillations were calculated. Single-submerged breakwaters were also used in the experiment for comparison. It is found that the single submerged breakwater has better wave interception, while the double-submerged breakwater has less mean water level change, less steady flow velocity, and less asymmetry wave profile of flow velocity at the bottom. It is also found that very low frequency oscillation arises in surface waves and flow velocity at the bottom, only for the single-submerged breakwaters.