www.ecn.nl

COMPARISON OF EXTREME LOAD EXTRAPOLATIONS USING MEASURED AND CALCULATED LOADS

Johan Peeringa and Erik KorterinkEWEC 2009, 18 March 2009, Marseille

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

Project

• Aim is validation of extreme value models by comparing extreme loads based on measurements and calculations.

‑ 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

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.

Method and distributions

• L-moment http://www.research.ibm.com/people/h/hosking/lmoments.html

• Generalized Extreme Value (GEV)

• Gumbel

• Lognormal

• Weibull

Free stream measured loads u= 15.5 m/s & t =1.75 m/s

1n

i }ixPr{X)iF(x

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%

Calculation of wake conditions

1. ECNWakeFarm

2. SWIFTwake

3. PHATAS

Comparison of empirical load distributions

Free stream condition

GEV Gumbel lognormal Weibul weibull (mom)

measured 115% 159% 126% 120% 118%

calculated 109% 129% 117% 108% 110%

Partial wake condition

GEV Gumbel lognormal Weibul weibull (mom)

measured 110% 154% 117% 115% 114%

calculated 254% 151% 200% 147% 129%

Full stream condition

GEV Gumbel lognormal Weibul weibull (mom)

measured 128% 158% 139% 129% 128%

calculated 109% 130% 116% 111% 110%

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.