New design concept to reduce the weight and cost of jacket foundations for offshore wind turbines

Jacket foundations for offshore wind turbines have yet to outperform monopiles for shallow waters and current generation turbines. However, a new concept for the design and fabrication of the jackets may change the balance in favour of jackets.

Jacket foundations are characterised by having tubular main legs and in between smaller cross stiffening tubulars welded in place between the main legs. The intersections between larger and smaller pipes - the tubular joints - are subjected to high loads and a high thickness is needed locally to achieve the required fatigue strength.

The EUDP project ‘A novel node design using HIgh strength steel for JACKet structure’ (Hi5Jack) will perform the necessary research and development enabling a reduction of the weight and cost of jacket foundations for offshore wind turbines. The means to reach this goal is to develop an innovative node design concept and to use high strength steel as an improvement of the traditional tubular joints.

The five partners behind Hi5Jack (Ramboll, SSAB, University of Southern Denmark, Bladt Industries and FORCE Technology) have estimated that the production cost of the jacket tubulars utilising the innovative joint concept can be reduced by up to 20%. Furthermore, the use of high strength steel will reduce the overall weight of the jacket, which is beneficial for both fabrication and installation.

The technology behind the novel node design is known from other areas; however, its application within offshore wind is new. The project will include design development of the most suitable configuration of the node concept and examination of the design’s impact on the global (frequency response) and local (fatigue and buckling) integrity of the foundations. Additionally, research will be conducted to further understand the fatigue performance of welded high strength steel and experimental industrial research activities will establish the fatigue design curves for the node.

“Ensuring a high durability of jackets is an essential part of sustaining the operation of wind turbines and reducing the costs of foundations will certainly support the further development of the offshore wind energy business. The project partners are very excited about taking part in this endeavour and we hope to reach solutions in support of the global objectives within energy and climate”, says Ronnie Refstrup Pedersen, Ramboll’s project manager in the EUDP project.

“In order to bring down the cost of energy it is essential to work together throughout the supply chain. We need to contribute with knowledge from each part of the supply chain to facilitate a more feasible fabrication of jacket foundations”, says Jacob Seier Nyvang, Design & Project Manager, Bladt Industries.

“Ground-breaking and innovative solutions are a continuing necessity to further bring down the cost of energy and ensure a transition to a sustainable future. We are excited to utilise our facilities and experience in validation to support the consortium in attaining what will surely be transformative solutions for offshore wind power”, says Eric Putnam, Head of Department, FORCE Technology.

“SSAB has a strong interest in enabling future growth with sustainability and if we in this case can support in taking out 20% of the steel in these huge constructions it is good use of our time and resources”, says Joakim Nyström, Global Sales Development Manager, Energy & Offshore.

Siemens Gamesa Renewable Energy and Vattenfall Offshore Wind support the Hi5Jack project as members of the Advisory Board.