Wave characterization for the diagnosis of semi-submerged structures

In order to assess the number of days per year an autonomous vehicle carrying a device to survey the envelope of the armour layer of rubble-mound breakwaters can sail close to the Sines' west breakwater, a general observed wave regime was established at a point in front of the breakwater, over depth contour -35.7m CD. For this, the relevant sea state parameters of 13463 wave records measured at the SINES 1D directional wave buoy were transferred to that point by linear interpolation of the results obtained in a transfer matrix between the measuring point and the point in front of the breakwater. This transfer matrix, specially created for this study, was defined by using the SWAN model for wave propagation assuming that the sea states could be characterized by a JONSWAP spectrum. The SWAN model and the nested grid scheme adopted proved adequate for this region. The results clearly show the influence of wave refraction on the sea states transferred to the point close to the breakwater. Assuming that the operational wave height limit of the autonomous vehicle is a significant wave height of 1.0 in, then from the general observed regime close to the break-water it may be concluded that the vehicle can operate in 27% of the time.