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Aero-elastic simulation of offshore wind turbines in the frequency domain
Gepubliceerd door: Publicatie datum:
ECN Windenergie 23-11-2009
ECN publicatienummer: Publicatie type:
ECN-E--09-060 ECN rapport
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The design and analysis of offshore wind turbines is a difficult task compared to onshore, due to the numerous load cases that have to be considered and the calculation work involved. Not only the amount of sea states to deal with at a specific site, but also the differences between sites and even between locations within a wind park should be taken into account for offshore wind energy. To ease this process, the use of the linearized frequency domain tool ECN TURBU, which is very fast compared to the commonly used nonlinear time domain tools, is investigated. TURBU is a fast fully integrated wind turbine design and analysis tool, which deals with aerodynamics, hydrodynamics, structural dynamics and control of modern three bladed wind turbines. The linearized wind turbine model is derived from geometric and material properties and site conditions. The system is then transformed to the frequency domain, useful for load calculation, stability analysis and control design. The wind, gravity, wave and water current loading are applied as input spectra to the wind turbine model. The results from load calculations can be analyzed both in the frequency domain (output spectra) and the time domain (simulations). Although frequency domain methods are common practice in offshore industry, the use of a fully integrated wind turbine design and analysis tool in the frequency domain is new to the wind energy sector. It requires a different design approach than conventional time domain tools, but creates opportunities as well due to quick feedback on the results during the design process. In this report it is shown how TURBU can aid the design of (offshore) wind turbines. A footprint of the wind turbine visualizing the effect of important design choices is constructed from output load spectra obtained with TURBU. Optimization using parameter variation can assist the designer in finding optimal settings for critical design parameters. Also the analysis of an offshore wind turbine with TURBU is addressed. It is used to identify the sea states contributing to fatigue, which reduces the number of sea states to analyse with nonlinear time domain tools. The results are compared to those obtained with a nonlinear time domain analysis tool (ECN PHATAS). Special attention is paid to the influence of the (linearized) hydrodynamics and the calculation method on the results.

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