Environmental Engineering Reference
In-Depth Information
2.6
20
Bea
m
1+BE
M
l
i
n
Beam1+BEM nonlin (pitch ex.)
Bea
m
2+F
r
ee
W
ake
(
p
i
tch excit.)
measurements (OMA)
2.5
15
2.4
2.3
10
2.2
5
2.1
2
0
1.9
1.8
-5
6
8
10
12
14
16
18
20
6
8
10
12
14
16
18
20
wind speed (m/s)
wind speed (m/s)
20
2
Beam1+BEM lin
Bea
m
1+BE
M
non
l
in (pitch ex.)
Beam2+FreeWake (pitch excit.)
measurements (OMA)
1.9
15
1.8
10
1.7
5
1.6
0
1.5
1.4
-5
6
8
10
12
14
16
18
20
6
8
10
12
14
16
18
20
wind speed (m/s)
wind speed (m/s)
Figure 18: Frequency and damping variation of the regressive (upper line) and
progressive (lower line) blade bending lag mode.
damping, non-linear models predict maximum damping. Note that in the longitu-
dinal tower mode the non-linear results resemble to the trends of the test data. The
best correlation was found for the “Beam2 + FreeWake” prediction which indi-
cates that non-linear effects play an important role in terms of accuracy. This point
is further supported by the results for the regressive and progressive lag modes of
the blade shown in Fig. 18. Both non-linear models provide good damping predic-
tions. In particular the “Beam2 + FreeWake” follows better the trend in the high
wind speed range. So in conclusion the validation procedure indicates that stability
modelling can reproduce the stability characteristics of wind turbines and that
predictions are on the safe side which is very important in design.
References
[1]
Meirovitch, L.,
Methods of Analytical Dynamics
, McGraw Hill: New York,
1970.
Zienkiewicz, O.C. & Taylor, R.L.,
[2]
The Finite Element Method
, Elsevier
Butterworth Heinemann, 2005.
Goldstein, H.,
[3]
Classical Mechanics,
Addison Wesley, 1980.
Mathematica, http://wolfram.com.
[4]
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