An Analysis of Working Sea States and Operational Ranges for the Gangway Equipped Offshore Wind Turbine Maintenance Vessels
During offshore wind turbine maintenance operations, maintenance vessels typically rely on transfer gangways to achieve safe transfer of personnel from the vessel to the wind turbine. With the development of offshore wind farms toward far sea areas, working sea state conditions have become increasingly complex. In recent years, the application of large-scale active wave compensation (AWC) transfer gangways has mitigated the adverse effects of ship motions on transfer operations to a certain extent, but the problem of limited motion ranges of each gangway joint has also emerged as a prominent issue. Under complex sea state conditions, if the station-keeping position of the maintenance vessel is improperly selected, joint limit violations may occur during the gangway compensation process, thereby posing safety risks. To address the above problems, this paper develops a novel geometric-envelope-based analytical method for operational sea states and ranges that explicitly accounts for gangway joint constraints and wave-induced vessel motions to meet the safety requirements of large-scale gangways. Subject to the motion constraints of gangway joints, to ensure that the initially selected station-keeping position of the vessel satisfies the requirements for safe gangway transfer, the feasible domain and motion range of the gangway base point under different sea states are obtained. By solving for the solutions where the motion range of the base point lies entirely within the feasible domain, feasible schemes for vessel station-keeping operations under different sea states are derived. The results show that the gangway can operate safely under sea states 3 and 4 but fails under sea state 5. The allowable height difference between the transfer point and the gangway base is [−2.7 m, 8.7 m] for sea state 3 and [1.8 m, 3.5 m] for sea state 4. The operational area on the horizontal plane presents a partial ring shape, and the ring width first increases and then decreases with increasing height difference. Finally, random numerical examples are designed to demonstrate the applicability and internal consistency of the proposed analytical method.