APPROACH TO WIND WAVE CORRELATION IN COUPLED ANALYSIS OF OFFSHORE WTG SUBSTRUCTURES

摘要

Offshore wind turbines need to be designed to withstand the expected environmental conditions throughout their design life, typically 25 years. It is current practice to perform structural analysis considering both wind and wave effects using time domain procedures, which can be very lengthy. Simplification of complex wind/wave relationships (speed, height, period and directionality) therefore needs to be undertaken in a realistic manner. Normally, the wind conditions are analysed in detail by the turbine supplier, however, the wave model is simplified by definition of sea states as a function of wind speed. Directionality of the waves is typically represented by misalignment relative to the wind. From wave loads perspective this approach might not accurately reflect the real wave climate at the site and hence wave fatigue damage may be estimated inadequately. A technique has been developed for calibrating the above simplified sea state definition using spectral fatigue analysis methods. Typical results are presented showing calibrated wind-wave data relations. The resultant calibrated wave fatigue conditions are then suitable for combination with wind conditions and will yield more accurate combined fatigue lives. This will allow effective structural designs of the substructure for wind turbines under combined wind and wave loading effects.