Page 294 - Wind Energy Handbook
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268 DESIGN LOADS FOR HORIZONTAL-AXIS WIND TURBINES
7
6
Second out-of-plane mode
6P
5
5P
Natural frequency (Hz) 4 First in-plane mode 4P
3
3P
2
2P
First out-of-
plane mode
1
1P
0
0 30 60
Rotational speed (r.p.m.)
Figure 5.27 Campbell Diagram for Blade TR
5.8.6 Response to stochastic loads
The analysis of stochastic loads in the frequency domain has already been described
in Section 5.7.5 for a rigid blade, and this will now be extended to cover the
dynamic response of the different vibration modes of a flexible blade using the
governing equation, Equation (5.70). Note that the restriction to an unstalled blade
operating at a relatively high tip speed ratio still applies.
Power spectrum of generalized blade loading
Ð R
The generalized fluctuating load with respect to the ith mode is Q i ¼ ì i (r)q(r)dr,
0
where
q(r) ¼ rÙ dC l u(r, t)c(r)r (5:25)
1
2 dÆ
