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Title:
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Some ideas on the modelling of atmospheric turbulence [ECN-RX--94-122]
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Author(s):
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Published by:
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Publication date:
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ECN
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1995
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ECN report number:
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Document type:
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ECN-RX--94-122
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Other
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Number of pages:
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Full text:
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11
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Download PDF
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Abstract:
In the introductory note to the IEA Symposium on Wind Conditions for WindTurbine Design 1994, the question is raised whether the actually occurring
extreme wind conditions, which recently lead to severely damaged wind
turbines, make a reconsideration and evaluation of the commonly used design
basis necessary. In addition several related questions were formulated of
which one is addressed here: 'Is the format of currently used design
guidelines concerning wind, i.e. extreme conditions and turbulence,
sufficient, is it too simple, does it cover all the relevant situations?' The
main line of thought is that we should seek for characteristic features in
the wind that are important for the (extreme) response of the wind turbine
structure. In the first section it is shown that next to strong gusts the
spatial distribution of wind speed variations should be included as a
characteristic feature that is important to system response. Gust models
should be replaced by (extreme) wind models based on stochastic wind field
simulation. The great number of time scales is another characteristic feature
of atmospheric turbulence. Only the shortest time scales, with a maximum
period of 10 minutes are included in load calculations. In section 3 it is
argued that the variation of hourly averages should be included, because they
can lead to a significant number of large load ranges, which in turn can lead
to low cycle fatigue. The last characteristic feature that is dealt with is
the randomness of the wind. Different realizations of a stochastic wind
field, which have the same statistics will generally lead to different load
spectra. Several realizations are needed to get a reliable estimate of the
highest load ranges. A few examples are shown. 8 figs., 6 refs.
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