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www.ecn.nl
COMPARISON OF EXTREME LOAD EXTRAPOLATIONS USING MEASURED AND CALCULATED LOADS
Johan Peeringa and Erik KorterinkEWEC 2009, 18 March 2009, Marseille
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Content
1. We@Sea project on extreme load extrapolation
2. ECN Wind turbine Test site Wieringermeer (EWTW)
3. Extreme load statistics
4. Results of measured free stream extreme loads
5. Calculation of loads in wake conditions
6. Comparison of measured and calculated extreme loads
7. Conclusions
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Project
• Aim is validation of extreme value models by comparing extreme loads based on measurements and calculations.
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‑ Research turbines numbered from 5 (most Westerly) to 9 (most Easterly)
‑ Wind farm line: 95-275 degrees
‑ MM3 at 3.5 D and 315 degrees from turbine 5
‑ MM3 at 2.5D and 31 degrees from turbine 6
-2000
-1000
0
1000
2000
-2000 -1000 0 1000 2000
Research turb
NM52
Meteo mast
Proto types
Single WEC
Meteo mast 3
Meteo mast 2 Meteo mast 1
1 km
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Statistical model
TVTVfTVLFLFTV
termshorttermlong dd),(),|(1,
turbwindenv v)tvtv |f(*)f(),f(
The long-term response distribution is the integration of the short-term response distribution, conditional on the wind speed (and turbulence), over all wind speeds.
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Method and distributions
• L-moment http://www.research.ibm.com/people/h/hosking/lmoments.html
• Generalized Extreme Value (GEV)
• Gumbel
• Lognormal
• Weibull
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Free stream measured loads u= 15.5 m/s & t =1.75 m/s
1n
i }ixPr{X)iF(x
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Free stream loads for different number of measurements used
60.1F(x(i))1)ixPr(X e
n GEV Gumbel lognormal Weibull Weibull (mom)
150 117% 158% 128% 123% 120%
100 115% 159% 125% 121% 119%
75 113% 160% 123% 120% 118%
50 113% 159% 122% 119% 117%
35 115% 159% 126% 120% 118%
20 112% 162% 122% 118% 118%
10 114% 176% 125% 124% 120%
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Calculation of wake conditions
1. ECNWakeFarm
2. SWIFTwake
3. PHATAS
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Comparison of empirical load distributions
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Free stream condition
GEV Gumbel lognormal Weibul weibull (mom)
measured 115% 159% 126% 120% 118%
calculated 109% 129% 117% 108% 110%
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Partial wake condition
GEV Gumbel lognormal Weibul weibull (mom)
measured 110% 154% 117% 115% 114%
calculated 254% 151% 200% 147% 129%
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Full stream condition
GEV Gumbel lognormal Weibul weibull (mom)
measured 128% 158% 139% 129% 128%
calculated 109% 130% 116% 111% 110%
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Conclusions
• For free stream measured loads the GEV, lognormal and Weibull distribution show good agreement with the empirical distribution.
• For the free stream measured loads 50 measurements are sufficient for the estimation of the distribution parameters.
• Calculated extreme flat blade root bending moments are smaller than the measured ones for all conditions at 15.5 m/s.
• Calculation methods for wake conditions should be improved.