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Title:
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Ontwikkeling en validatie van een stochastisch windbelastingsmodel. Deel 1. Windmodellering
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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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1-12-1996
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ECN report number:
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Document type:
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ECN-C--96-096
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ECN publication
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Number of pages:
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Full text:
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66
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Download PDF
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Abstract:
The considerations that led to the choice of a stochastic turbulencemodel for normal wind conditions are described in terms of spectral density
functions and spatial coherence functions for the three components of the
wind speed vector. This turbulence model should be used in design load
calculations on horizontal axis wind turbines. The model should comply with
the IEC 1400-1 standard and should produce design life time fatigue load
spectra which are at least as severe as the corresponding load spectra based
on the Dutch 'Handbook for Wind Turbine Design Version 3'. For the
longitudinal component the IEC standard proposes three combinations of
spectral density function and coherency function, which are not
interchangeable. Based on a qualitative evaluation of the spectra of
rotationally sampled wind speed it is concluded that the Von Karman spectral
model is not adequate for fatigue life time calculations, leaving only the
exponential coherency function in combination with either the Kaimal spectrum
or the Von Karman spectrum as an acceptable choice. Based on validation
calculations, reported in part 3 of this report, it is finally concluded that
the Von Karman spectrum in conjunction with the exponential coherency
function should be used. The IEC standard only specifies spectral density
functions for the transverse and vertical component. The missing spatial
coherency functions for these in-plane components are taken from other
sources, most notably ESDU. In addition, the complete set of spectral
functions of the Von Karman isotropic turbulence model is derived. This
enabled the assessment of the importance of cross couplings between the three
components and showed how the direction of the separation influences the
coherency functions. It is concluded that only the cross coupling between the
u- and w-component is of importance. The direction of the separation does
have a significant influence on the coherence. Because a uniform coherence
facilitates efficient simulation some measures are taken to eliminate the
directional dependence of the coherence. To ensure good quality wind
simulation guidelines are given to determine values of important parameters,
e.g. the length of the wind field simulation, the time step in the wind speed
time series and the number of points in the rotor plane at which the wind
speed time series are generated. In the second volume the aeroelastic models
of three wind turbines are constructed and calibrated. In the third volume
these models are used to validate the stochastic turbulence model proposed in
this volume. 12 figs., 1 tab., 2 appendices, 24 refs.
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