AbstractsPhysics

Today’s increasing attention to offshore wind turbines as a renewable source of energy leads to new problems from the logistics point of view. As a consequence of new generation wind farms being built and planned to be built further offshore, as far as 150-200km from the shore, current transportation concepts that are used for wind turbine maintenance are considered to be less efficient. Among others, KNUD E. HANSEN A/S has developed a new transportation concept as a solution to this problem. This concept makes use of several vessels of which only one of them, namely the crew transfer vessel (CTV) with a length overall of 30 m is handled in this report. The CTV is to be docked onboard of a larger service operation vessel (SOV) with a length over 100m. The concept all together is expected to reduce the operational costs and increase the accessibility of wind farms for maintenance operations. As a part of the concept, design requirements are set for 3 operational conditions, where the first is calm water operations, prioritizing maximum design speed; the second is poor weather conditions up to 2 meter significant wave height prioritizing low level vertical motions, where the vessel is still operable for crew transferring; and bad weather conditions with sea states higher than 2 meter significant wave height, where the requirement for high range and reserve provisions for 1-2 days sailing is of high importance. Hull form, general arrangement, propulsion system and onboard equipment are examined closely to provide a design that fulfills the requirements. Especially large waterplane area is found to be crucial to minimise the vertical motions. Furthermore a docking arrangement and crew transferring equipment are designed. Aside the shorter wave periods in the region of 3-4s, the vessel fulfills all the operability requirements in transit stages, which is set at 2 meter significant wave height, as demonstrated by the seakeeping analysis. As suggested in the report, the performance can be improved by following the recommendations of this report. Furthermore, proposed novel designs for launching and retrieving mechanism in the dock of the bigger vessel has been demonstrated to be operable up to sea conditions with significant wave heights of 2.5 m, as desired. The proposed wind turbine access system is expected to be operable up to sea conditions with significant wave heights of 2 m by further improving the design according to the design suggestions, which are made as a result of the time domain analysis. The concept design study demonstrates that it is feasible to improve the current design by following the work, results and recommendations that are described in this report, in the following design stages into a final product. This can be used successfully as a part of the transportation concept in order to improve the overall efficiency of the offshore wind farms, increasing the interest for energy companies.