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 produc tion systems have a particularly complex response; hypothetical studies sug gest that the greatest forces occur when the wind and waves are non-colline ar. In order to determine whether any significant non-collinearity is obser ved in practice, directional environmental data from three sites were analy sed. Various circular statistics were determined and empirical probability density distributions constructed to provide an insight into the directiona l relationships of the offshore environment. These suggest that while the w ind and waves are usually well aligned at the peak of the typical storm, th is collinearity is not always observed. Before the storm is fully developed , but when the mean wind speed and significant wave height are already larg e, the wind and waves may be poorly aligned with a directional difference o f up to 60 degrees. Such conditions may result in the greatest mooring forc es on a single point moored system and should be considered when specifying the typical 50 year conditions for the design requirements of floating sys tems. (C) 2000 Elsevier Science Ltd. All rights reserved.