Multi-mode reliability analysis of mooring system of deep-water floating structures

摘要

This paper proposes a comprehensive method for reliability analysis of a deep-water mooring system. The novelty of the newly developed method is that it considers the failure modes of floater offset excess (the function of the intact mooring system), mooring line breakage (safety), and fatigue (persistence) as part of the mooring system's reliability assessment. In addition, the quantitative relation between mooring line breaking strength and cumulative fatigue damage is considered. In this research, the annual maximum floater offset and mooring line tension are calculated based on the wave condition with a 1-year return period. Long-term mooring line tension ranges are obtained from coupled analysis in the time domain for all the sea states in the wave scatter diagram and the fatigue damage is assessed using the Palmgren-Miner rule and T-N curve. Then, the mooring system's reliability is investigated by running Monte Carlo simulations. The results demonstrate that the failure probability considering the three failure modes is much greater than that of any single mode and neglecting the correlation between different failure modes leads to significant underestimation of the mooring system failure probability. Moreover, the sensitivity analysis indicates that the underestimation proportion is obviously affected by the fatigue exponent (m).