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Operational Modal Analysis for Assessing the Dynamic Behaviour of Wind Turbines
Figure 5: Two of the Experimentally Identified Mode Shapes of the Carrier Structure
Figure 6: Calculated Mode Shapes Based on the Comprehensive Wind Turbine Finite Element Model
(Experimental Counterparts Are Shown in Figure 5)
measured and calculated modes. We identified deviations in the In summary, we have proved that OMA is a highly practical
resonant frequencies of up to 25%. Deviations of this size can become experimental tool for precise modal parameter assessment of wind
serious if a critical excitation exists. Hence, we applied a computational turbines. The advantage of utilising the stochastic structure excitation
model updating (CMU) procedure to minimise the deviations of the FE induced by wind and the easy-to-handle parameter estimations make
model compared with the real structural behaviour. In particular, we OMA useful not only for scientific institutions but also for practical
had to improve the modelled distribution of equipment masses applications in industry.
(converter, transformer, generator, cabin, etc.). We plotted two of the
calculated mode shapes of the updated carrier structure extracted Let us close with a quote found in a ship-building journal from the
from the comprehensive wind turbine FE model (see Figure 6). These 1970s: “No-one believes experimental data except the man who takes
two shapes correspond to the two measured mode shapes in Figure 5. it, but everyone believes the results of a theoretical analysis except the
The very good agreement is visually evident. We also achieved very man who makes it”. More than 30 years later, and regardless of the
good agreement for other, more complex and less visually technical developments in the meantime, this thinking is still popular.
comprehensible mode shapes. More measurements in combination with the validation of simulation
models may close the gap between the experimental and the simulated
Another useful result of this low-cost measurement is that we are now world. We believe we have advanced this cause. n
able to provide accurate excitation data to component suppliers, such
as transformer suppliers. Moreover, an exciting prospect for the future Acknowledgements
is expansion of the technique described here to the main drive train in The authors wish to thank René Steputat for his accurate work on the
order to obtain more insight into this complex component assembly FE modelling and analysis and Dr Jennifer Seachrist for her valuable
and to verify our simulation models. contribution in editing this article.
MODERN ENERGY REVIEW VOLUME 2 ISSUE 1
62
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