Extreme mooring tensions due to snap loads on a floating offshore wind turbine system

We propose a composite Weibull probability distribution for the mooring line dynamic tension that incorporates the effects of snap events. The model is composed of two Weibull distributions with different characteristics on either side of a transition tension value, and whose parameters are estimated from test data. The transition tension is related to the maximum cyclic dynamic tension in an extreme storm event, as specified by recommended practices. The proposed distribution model provides a good fit to the measured tension data, particularly in the extreme range. A design extreme value is developed for systems where snap loads are generally non-existent or are associated with very low probabilities of occurrence. When the shock load incidence probability is higher, the developed composite Weibull distribution model could offer a good starting point for the prediction of extreme dynamic tensions of a FOWT mooring system.