MHI Vestas Offshore Wind has contracted the Hamburg-based design and engineering company HeavyLift@Sea GmbH to design grillages for the sea fastening of wind turbine blades built for DONG Energy’s 258 MW Burbo Bank Extension offshore wind farm.
The 80-metre-long blades are part of the 32 MHI Vestas V164-8.0 MW turbines, the first components of which have already reached the pre-assembly site at the Belfast Harbour.
The blades are manufactured at the MHI Vestas factories in Nakskov, Denmark, and Isle of Wight, UK, and shipped on board a multipurpose vessel to Belfast.
In general, wind turbine components are solely designed for in-situ handling and not for transportation. Ship motions cause stress fluctuations in the tension-compression range. This can make the sea fastening likely to suffer from fatigue.
The main design challenges result from the constrained space available onboard the nominated vessel, the utilization of the ship’s own lifting gears and a stress protected, safe loading and discharging of the blades.
The grillages were designed to be easily installed and dismounted in order to keep the vessel flexible for alternative project transportation, HeavyLift@Sea said. Technically, the design of the grillages had to meet the requirements of the existing stack frames. The forces resulting from the sea motion were distributed equally into the vessels structure.
This subject was a main issue due to the restricted deck strength of the nominated MPV. A detailed FE-analysis was performed to ensure the strength of the structure and the vessel itself. In total 2 frames and 2 grillages were designed with a total weight of about 12t.
The first shipment of stacked blades on the nominated vessel was done in July 2016.
The Burbo Bank Extension is being developed by Burbo Bank Extension Ltd which is owned by DONG Energy Wind Power (50%), PKA (25%) and Kirkbi A/S (25%).
The wind farm, located 8 kilometres off the coast in Liverpool Bay, is an addition to the operational 90MW Burbo Bank.