GUST LOADING FACTORS FOR TENSION LEG PLATFORMS

Utilization of tension leg platforms for deep water oil recovery has increased the importance of accurately predicting the effects of wind on these structures. The gust loading factor approach incorporates the effect of deviations from mean wind speed, gustiness, on structures based on extreme value statistics. Single-point representation of the wind field may be employed for structures smaller than typical gust size, but partial wind velocity correlation over large structures necessitates the use of multi-point wind field statistics to determine dynamic load effects. The characteristics of the wind field over the ocean are reviewed, and a previously reported description of an ocean-based wind spectrum is further examined in the light of additional full-scale offshore measurements. A modified coherence function for offshore applications is presented based on theoretical considerations and experimental data. A random vibration-based formulation of gust loading factors is presented that accounts for the hydrodynamic damping imparted by the platform motions in waves and currents. The response statistics of an offshore platform are predicted in the light of parametric uncertainties by a Monte Carlo simulation using the gust loading factor approach. This is used as the basis for a reliability analysis of the platform.