Physical and numerical analysis of a concept offshore wind farm service vessel hull design

Wind turbine maintenance and access during high sea states is a key issue for the successful operation of an offshore wind farm. Currently there is a 1.5m significant wave height (Hs) limit for the standard 'step over' method of transferring personnel to an offshore wind turbine. Increasing the Hs that offshore wind turbines can be accessed at would reduce the lifetime, levelised cost of energy and address a health and safety issue. The paper addresses this issue by examining a concept hull design for an offshore wind farm service vessel. The proposed design reduces the vessel's heave and motion by dampening its response to the wave motion. The design underwent both numerical and physical methods of testing. The numerical modelling was carried out in a 3-D wave basin built in ANSYS CFX and is based on symmetry across the hull which allows for three degrees of freedom. Physical modelling at 1:25 scale took place in the wave basin at Beaufort Research in University College Cork. A number of variations of the concept were tested and the results showed the aspects of the concept that could be beneficial to personnel transfer, through reduced response amplitude operators at zero forward speed.