Daniel KauferValidation and Applicability of an Integrated Load Simulation Method for Offshore Wind Turbines with Jacket Structures | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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ISBN: | 978-3-8440-6069-0 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Series: | Luft- und Raumfahrttechnik | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Keywords: | Offshore Wind; Support Structures; Simulation; Measurements | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Type of publication: | Thesis | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Language: | English | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Pages: | 212 pages | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Figures: | 115 figures | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Weight: | 315 g | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Format: | 21 x 14,8 cm | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Binding: | Paperback | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Price: | 49,80 € / 62,30 SFr | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Published: | July 2018 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Abstract: | Today the design of offshore wind turbines is an iterative process between different designers of special roles in order to ensure a cost-efficient solution. Responsibilities in offshore business are clearly split between the wind turbine designer and the support structure designer. A major collaborative task for both parties is the determination of the governing design loads due to the site-specific and stochastic met-ocean conditions over the lifetime including transport, installation, operation and decommissioning phases. The design calculations for the operation require an integrative model approach, which is able to consider all relevant subsystems and the governing loads. In general, these subsystems are the rotor, controller, nacelle, tower, substructure, foundation and soil. Common practise in industry application is that specialized structural models are applied for the wind turbine (i.e. rotor, tower, nacelle and controller) and the support structure (substructure, foundation and soil). Each of the specialized models considers an approximated and temporal constant model of the other subsystem during the design load iterations. For many applications this is a valid approach, but it can have disadvantages when dynamic interactions between the wind turbine and the support structure become excited or the natural frequency of the full system changes during subsystem optimization.
In this thesis an integrated model has been further developed and applied, which facilitates the combination of the wind turbine and the support structure in one direct solution by coupling the equations of motion during runtime. This ensures full dynamic interaction of the models without further simplification of the original models. Two applications have been realised: Flex5 coupled to Poseidon and Flex5 coupled to ANSYS. The coupled models are verified against other state-of-the art load simulation tools to proof the correct implementation. In a next step the simulation method is validated against measurements from a commercial offshore wind turbine. The measurement campaign is carried out in the wind farm Alpha Ventus, the first commercial wind farm in the German North Sea. The considered wind turbine is a Senvion 5M installed on a jacket in 28m water depth. The validation considers mainly the strain gauge measurements from the rotor blades, the tower and the jacket substructure at different operational states of the wind turbine. High resolution data and the derived statistical parameters are taken into account for the validation. The results consider natural frequencies, quasi-static loadings, time series, statistic parameters, damage equivalent loads and rainflow count distribution. Correlated wind and wave conditions from a nearby met-mast are used directly in the simulation model. In conclusion very good consistence between load measurements and the results from the integrated simulation approach is shown. Some differences remain because the turbulence of the wind field and the elevation of the random sea state do not correspond with the model in detail. The spatial and temporal resolution of the wind and wave data was not measured. This highlights the necessity of very accurate and correlated measurements of wind and waves for the design of offshore wind turbines and the relevance of models that can process more complex data. The final part of the thesis addresses the distinctions between different simulation approaches compared to the newly developed fully-integrated approach for offshore wind turbines with jackets. The three alternative models differ mainly in the accuracy of the jacket subsystem or the limited dynamic interaction between wind turbine and support structure. For most components like the blades, the tower or the jacket legs good correspondences between the simplified models and the fully-integrated model are achieved. Larger differences occur in the local stresses of the jacket brace elements. This has a significant impact on the hot-spot stresses of tubular joints, which can be decisive for the entire jacket design. It is therefore recommended to use a fully-integrated model that is able to capture the dynamic interaction between wind turbine and local support structure components. |