HBM strain gauges and data acquisition equipment were used in a unique experiment performed in the Westermeerwind wind farm in the Netherlands to investigate the damping effect of the sea bed on the loads on wind turbines.In order to make wind energy more attractive than fossil power and also as a result of the effects of competition, providers are searching for new ways of supplying the required megawatts in as economical a way as possible when constructing offshore wind farms. Many technical innovations in the areas of masts, turbines, and rotors have therefore been introduced in recent years to achieve this. Siemens Windpower has started a project to gain more insight into the interaction between the sea bed and the wind turbine foundations. HBM strain gauges and data acquisition equipment were used in a unique experiment performed in the Westermeerwind wind farm in the Netherlands to investigate the damping effect of the sea bed on the loads on wind turbines. The goal was to obtain reliable input parameters for a standardized design process for wind turbine foundations. Siemens Windpower is a new company that has been an independent part of Siemens AG since 1 January, 2017, combining a number of existing Siemens divisions and acquisitions that deal with wind energy. Siemens Windpower B.V. in the Netherlands has grown, in the meantime, into an organization with around 120 staff. It maintains existing wind farms and also takes care of the engineering and project management for constructing new wind farms. Thanks to its collaboration with the TU Delft, Siemens Windpower in the Netherlands has gradually evolved into a Centre of Competence for the development and construction of wind turbines. The emphasis is on calculating loads and designing the masts and foundations. Research into developing and manufacturing the turbines is carried out mainly by the company’s Danish branches.
“The price tag for a wind farm with an output of 100 MW that consists of 13 wind turbines of 8 MW each is naturally much more attractive than one with 25 wind turbines that deliver 4 MW each.”
The correct prediction of this frequency is very important, but the major uncertainty factor is the interaction between the structure and the sea bed.The stiffness of the soil is generally underestimated in the case of current structures, with the result that structures are calculated conservatively, stronger foundations are designed and more steel is used. The logical consequence is that the price of the wind turbine increases, which is an undesirable occurrence in a highly-competitive market that is subject to high pressure on prices.”
The condition of the sub-sea soil is therefore an important starting point when designing wind turbines, and an extensive soil survey yields better input parameters for designing the foundations.We wanted to map out and validate this relationship in the Disstinct project, not just using computer models but also in practice, and that’s what we did when constructing the Westermeerwind wind farm.” This wind farm lies in the IJsselmeer, along the coast of the North-East Polder, just to the north of the town of Urk. It generates 144 MW, which is sufficient to provide power to 160,000 families. The 48 Siemens wind turbines are arranged in two rows and are spaced some 400 to 500 meters apart. They are 95 meters tall and the rotors are 108 meters in diameter. The water they stand in is 4 to 7 meters deep. Siemens was the turnkey contractor for the wind farm, which was constructed together with Van Oord, BM4Wind, and VMBS in a contract from Westermeer Wind B.V. The wind farm was officially commissioned by Minister Kamp of Economic Affairs on 21 June, 2016.
"There are two ways of attaching a strain gauge, gluing or spot welding; and gluing turned out to be the only option for this project because the monopile had already been certified.”
We want to use all these data to develop a design model that can be certified by DNV-GL and, thereby, become a sort of standard or reference for designing offshore wind turbines.The consequence will be that more extensive soil surveys will be carried out in the future at the wind turbine locations than is the case at the moment. That is only a small additional investment, but it can be recovered quickly because the foundations and the mast will be lighter, and therefore, cheaper.”