ECN publication
TURBU Offshore, Computer Program for Frequency Domain Analysis of Horizontal Axis Offshore Wind Turbines; Implementation
Published by: Publication date:
ECN Wind Energy 1-9-2004
ECN report number: Document type:
ECN-C--04-079 ECN publication
Number of pages: Full text:
309 Download PDF  


The design of offshore wind turbines requires to assess a huge amount of different seastates and wind conditions. Therefor the calculational efficiency of a combined time/frequency domain approach is attractive. This was the reason for the development of the frequency domain tool TURBU Offshore. In addition, such a tool is very feasible for parameter studies; the dynamics of large offshore wind turbines use to be highly sensitive to the natural frequency values. The implementation of TURBU Offshore is based on a modular linear model, with control loops included. The assumptions for structural and aerodynamic modelling are state of the art. A multiblade transformation for threebladed rotors eliminates the rotational coupling between the blades and the tower. Twobladed rotors require a general handling of this coupling, which is however enabled by the model setup.The program provides the mean loads, power spectra and periodic loads, which are merged to overall load histories for fatigue assessment. Besides, the power spectra make clear the relevance of poorly damped deformation modes.

Verification exercises point out that TURBU Offshore works well in stationary conditions and that it predicts damping rates and natural frequencies properly. It is expected that the use of TURBU Offshore in the design of wind turbines will yield substantial cost reduction for the nacelle, rotor and tower.

It is recommended to develop guidelines for the complementary use of TURBU Offshore with a time domain tool. The derivation of submodels for control design will be useful, just as the coupling of the linear structural dynamics model to an advanced aerodynamic code.

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