Reliability Assessment of a FPSO Hull Girder Subjected to Degradations of Corrosion and Fatigue

摘要

This paper presents a reliability assessment of a FPSO hull girder subjected to degradations due to corrosion and fatigue. The corrosion defect is considered a random process with a constnt corrosion-rate. The crack propagation is predicted based on a Paris-Erdogen equation. A simplified method is introduced to predict the ultimate strength of a hull girder using an effective width of plating and beam-column formula. 'Failure' occurs when the combined value of stillwater and wave-induced bending moments exceeds the ultimate strength of the hull girder. The Ferry-Borges method is applied to combine the stochastic processes of stillwater and waveinduced bending moments. an efficient response surface approach is used to evaluate the failure function at sampling points. A modified Monte Carlo simulation technique is applied to evaluate the failure probability. The time-variation reliability and the uncertainties in design variables, are quantified including stillwater & waved-induced bending moments, yielding strengths, elastic modulus, residual deflections, corrosion rate and crack size. The modeling errors, e.g. for loadign and strength, are also quantified.