Directional statistics of the wind and waves

Wind, wave and current each make a significant contribution to the mooring forces experienced by floating systems. Single point moored floating production systems have a particularly complex response; hypothetical studies suggest that the greatest forces occur when the wind and waves are non-collinear. In order to determine whether any significant non-collinearity is observed in practice, directional environmental data from three sites were analysed. Various circular statistics were determined and empirical probability density distributions constructed to provide an insight into the directional relationships of the offshore environment. These suggest that while the wind and waves are usually well aligned at the peak of the typical storm, this collinearity is not always observed. Before the storm is fully developed, but when the mean wind speed and significant wave height are already large, the wind and waves may be poorly aligned with a directional difference of up to 60 degrees. Such conditions may result in the greatest mooring forces on a single point moored system and should be considered when specifying the typical 50 year conditions for the design requirements of floating systems. (C) 2000 Elsevier Science Ltd. All rights reserved.