Combined oceanographic criteria for deepwater structures in the Gulf of Mexico

Copyright 1991, Offshore Technology Conference. The strongest winds, waves, and currents do not necessarily occur at the same time in a storm, and it is unnecessarily conservative to set design criteria as if they did. We hindcast the most important hurricanes to affect the northern Gulf of Mexico in the twentieth century using the ODGP-2 model for winds and waves and the Mellor-Durbin turbulence closure model for currents. To account for the effect of the joint occurrence of wind, wave and current, we used generic structure models of a rigid platform, a compliant tower, and a tension leg platform to integrate forces. Response functions for the structures were developed through numerical simulations in random waves. Multivariate regression analysis then produced simple polynomial equations for the responses which could be applied to the entire database of oceanographic hindcasts. For the fixed platform, the 100 year base shear found from using this method was approximately 15% less than that which resulted from applying the 100 year oceanographic conditions for winds, waves and currents simultaneously. For a given force level, the hindcasts indicate that a larger proportion of the total force is due to the current than has been thought previously. For the TLP, combined oceanographic criteria which include directional effects were developed. The most likely sea state to cause the 100 year minimum tendon tension was found to occur near the eye of a hurricane.

Combined oceanographic criteria for deepwater structures in the Gulf of Mexico Conference Paper