Abstract
Today, design of wind turbines is extensively done by the implementation of numerical models. These
models simulate the dynamic behaviour of full-scale wind turbines which helps to ensure the structural
integrity of prototypes. However, these numerical models need validation from experimental results,
and in turn, numerical and analytical modelling help improve and validate new experimental techniques.
Wind turbines are complex dynamic systems that consist of mutually moving substructures under high
dynamic loads. At a standstill, the system can be modelled as linear time-invariant (LTI), and modal
analysis requirements are thus fulfilled for the dynamic characterization. Under operation, the system
cannot be considered as LTI and must be modelled as a linear periodic time-variant (LPTV) system,
which allows for the application of the related theory for such systems. One of these methods is the
Coleman transformation, which transforms the vibrations expressed in the blade rotating coordinates to
the fixed-ground frame of reference. The application of this transformation, originally from helicopter
theory, allows for the conversion of a LPTV system to a LTI system under certain assumptions, among
which is the assumption of isotropic rotors. Since rotors are never completely isotropic in real life, this
paper presents the application of operational modal analysis together with the Coleman transformation on
both experimental data from a full-scale Vestas wind turbine with instrumented blades and nacelle, and
its representative numerical model with a fully isotropic rotor. The results show that the first tower and
rotor edgewise modes are well identified, and that the rotor edgewise modes can be identified from the
nacelle signals. The results also uncover the challenge the excitation forces imply for the identification
of flapwise modes.
Original language | English |
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Title of host publication | Proceedings of the 6th International Operational Modal Analysis Conference (IOMAC 2015) |
Number of pages | 10 |
Publication date | 2015 |
Publication status | Published - 2015 |
Event | 6th International Operational Modal Analysis Conference - Gijón, Spain Duration: 12 May 2015 → 14 May 2015 |
Conference
Conference | 6th International Operational Modal Analysis Conference |
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Country/Territory | Spain |
City | Gijón |
Period | 12/05/2015 → 14/05/2015 |
Keywords
- Wind turbines
- Structural dynamics
- Operational modal analysis
- Modal parameters
- System Identification
- Anisotropic rotors