Some results from the analysis of metocean data collected during storms in the northern North Sea

This paper presents the results from statistical analyses of wave and wind data collected over a period from August 1994 to June 1998 at the North Alwyn, fixed, oil and gas platform in the northern North Sea. Theoretical joint probability distributions of individual waveheight and periods are found to provide a poor fit to data sets obtained by aggregating the individual waves into bins defined by the significant waveheight, H_s, and average zero-crossing period, T_z, of the 20-minute interval in which the waves were observed. Better fits are obtained when empirical models are used for the joint probability of individual waveheight and steepness, and a general bivariate Weibull model is presented that is conditional upon significant waveheight and average zero crossing period. The JONSWAP spectrum peak enhancement parameter ? is found to vary significantly for the storm seastates examined.