Probabilistic multilevel robustness assessment framework for a TLP under mooring failure considering uncertainties

In recent years, mooring failure is one of the prone accidents of floating production system (FPS). And it may lead to catastrophic consequences, due to lack of structural robustness, the ability to withstand progressive failure. During their operational life, Tension leg platforms (TLPs), as a kind of FPS, are exposed to stochastic loading (e.g., wind, wave and current) and perform stochastic dynamic response; on the resistance side, moorings also behave in a stochastic way. In this piece of research, a probabilistic multilevel robustness assessment framework is proposed to effectively evaluate robustness of TLP under mooring failure. For comprehensive assessment, the final robustness curve is obtained by weighting three kinds of major progressive failure modes, that is, progressive tendons failure, excessive offset and capsize. To fully consider uncertain factors, the proposed method includes probabilistic model of response based on hydrodynamic analysis, probabilistic model of ocean environment and probabilistic model of resistance. An illustrative example is developed as a walk-through of proposed methodology, discussing possible outcomes. The results indicate that combinations of failure tendons, classified by tendons’ relative position and their relationships with loading direction, would greatly influence structural robustness; besides, upgrade of tendons couldn't comprehensively improve robustness.