Environmental Engineering Reference
In-Depth Information
Table 11-4.
Comparison of Two Modes from a Parked AOC 15/50 HAWT
Using NExT and Impact Excitation
[Rumsey
et al
. 1997]
Mode
Frequency (Hz)
Damping (%)
Impact
NExT
Impact
NExT
Teeter
3.19
3.18
1.18
1.58
Umbrella
3.72
3.73
1.11
1.27
Figure 11-12. Damping versus wind speed for the 5.34 Hz edgewise mode of the North-
ern Power Systems 100-kW HAWT.
[James 1994]
A more challenging dynamical system is a free-yaw HAWT with its rotor mounted down-
wind of the tower. This turbine configuration can be simpler to build, but the uncontrolled
yaw degree-of-freedom couples to the other in-plane dynamic modes and creates entire fami-
lies of frequency-dependent phenomena. Figure 11-13 shows an example from the free-yaw
26-m diameter
Advanced Wind Turbines
AWT-26, which is a downwind teetering-rotor ma-
chine [Malcolm and James 1995]. The expected per-rev harmonic forcing function frequen-
cies are plotted as the dotted lines. The solid lines denote the analytically-predicted natural
frequency families. These frequencies are only distinct in the non-rotating condition.
As the machine rotates, natural frequencies split into multiple rotation-rate dependent
frequencies. NExT was used to process field data from this HAWT as it was rotating at 58
rpm. There is a slight mismatch between the analysis and the field test data. This mismatch
illustrates the utility of extracting structural dynamics data from an operating machine for
comparisons to analytical data.
Search WWH ::
Custom Search