Nested reliability analysis of mooring lines for floating systems

A formulation for the nested reliability analysis of mooring lines is presented, which handles the uncertainty in the maximum dynamic line tensions that is assessed conditional on the uncertain environmental variables describing extreme sea states. The formulation is applied to calibration of partial safety factors for the ultimate limit state. Response surfaces are used to describe the mean line tension and the probability distribution parameters of the maximum dynamic tension as functions of the environmental variables. The appropriateness of using simplified formulations of the maximum dynamic tension in the limit state function is examined, as well as the effect of reducing the number of environmental variables that are treated as uncertain. Numerical results are given for mooring lines designed for FPSO systems at 500m, 1000m, and 1500m water depths in the Bay of Campeche (Gulf of Mexico) using environmental models based on hurricane and storm hindcast data. (C) 2011 Elsevier Ltd. All rights reserved.