Joint Probability of Extreme Waves and Currents on Norwegian Shelf

Simultaneous wave and current measurements on the Norwegian Shelf were used to estimate the appropriate current to associate with extreme waves in platform design. The primary data consisted of seven years of measurements at Tromsoflaket ($71°30\prime N\text{,}$ 19 °E, 230 m depth), including 38 storms with peak significant wave heights above 7 m. The maximum wave height and maximum current occurred simultaneously in only one of the 38 storms. The wave and current timeseries data were used to calculate the time series of drag load on a simple structure and statistics of wave height and drag load were developed. The data showed that the in‐line current that must be added to extreme waves in order to preserve the extreme loads approaches 25 cm/s asymptotically as storm severity increases. Sensitivity studies suggest that this limit is largely insensitive to reasonable variations in current profile, wave kinematics theory, structure geometry, tidal current removal, length of data base, or site location. These results show that the current specified by Norwegian regulatory authorities is conservative, and provide a basis for reducing the design hydrodynamic loads on drag‐dominated offshore structures on the Norwegian shelf.