Parallel Force/Position Control of Motion Compensated Gangway in Offshore Operations

Ship-based motion compensated gangway systems are one of the most economical and effective access systems for the transportation of maintenance personnel, equipment, and spare parts to offshore wind turbines. During the transferring operation, the gangway passageway connecting the ship and the wind turbine is either landed on top of the wind turbine platform or pushed against to it via bumpers or similar clamping mechanisms. Considering the limited space and weight of wind turbine platforms, the latter is usually preferred. However, in either case, the contact force to the gangway is hard to control with pure active motion compensation. Consequently, it may damage the wind turbine and the gangway, and affect the dynamic positioning of small weight-class vessels. Current applications usually include passive systems to provide the flexibility to the gangway movement, or with a free end at the gangway tip. This study introduces a parallel force/position control algorithm for the control of the contact force between the gangway tip and the platform during motion compensated operations. Model development of the dynamic systems including the hydraulic power systems and the multi-body dynamics of gangway are described. The proposed parallel position/force control algorithm is verified through simulations.