Persistence-based operability for time-constrained onsite installation of floating offshore wind turbines: Poisson interval framework

Onsite installation of floating offshore wind turbines requires crane-mating of a turbine assembly onto a floating spar within a short window of low relative motion. Operability is conventionally judged by a peak criterion, which checks whether the extreme response stays within an allowable limit but not whether a feasible window of sufficient duration occurs. A persistence-based framework is proposed in which operability is defined by the probability that the longest contiguous feasible interval within a sea-state block reaches the required execution time. A closed-form estimator is derived from time-domain simulation data. The framework recovers the conventional peak criterion as the limiting case. A maximum operable execution time is also introduced as a scalar margin metric across task durations. Applied to 72 installation conditions across three catamaran-based configurations, the framework identifies 22 of 72 conditions as operable against 8 under the peak criterion. In these additional cases, brief intermittent exceedances coexist with feasible windows that remain long enough for the operation, a structure the peak criterion cannot capture, making it over-conservative at this execution time. The direction of this conservatism reverses between 120 s and 300 s, placing the required execution time on equal footing with significant wave height and peak period as an operability parameter.