USING WIND, WAVE AND CURRENT TIME HISTORIES TO ESTIMATE REALISTIC EXTREME JOINT LOADING CONDITIONS

The paper describes an environmental monitoring program in place on the North Alwyn platform operated by Total Oil Marine in the northern North Sea. It uses an intelligent data-logging system to record the wave, wind and current conditions at a high sampling rate. For storm conditions the raw data is saved and under calmer conditions, all wave height/wave period pairs are stored along with summary wind and current conditions for use in fatigue studies and long term probability models. Analysis of the time histories is aimed at the time-domain correlation of the directional loading constituents to give a more realistic extreme loading envelope than is possible from gross summary statistics. A joint probability model is also being developed for wave, wind and current conditions. Illustrative examples of temporal and directional discrepancies between maxima of wind and wave traces are presented to provide a comparison with the more common assumption that the worst overall conditions is represented by the simultaneous occurrence of the worst case of each of the environmental loading factors.