Advanced Wind Turbine Program Next Generation Turbine ... - NREL

2.3.1.2 Machine Carrier Yaw and Nodding Compliance
GE commissioned two studies to investigate the impact on loads from introducing compliance
about the drive train tilt (or nodding) and yaw axes. Both studies were conducted using the baseline
750i turbine as the study control. The studies were conducted in slightly different ways.
Figure 8 illustrates the results of introducing yaw and nodding compliance as determined by the
first study for different values of natural frequency and damping for each degree of freedom.
Flap bending moment, tower top yawing moment, and hub (shaft) bending moment are all most
strongly affected by the addition of yaw compliance, with the nodding, fixed yaw cases providing
little or no load relief. Tower top yaw moments are further reduced by increased softening of
the yaw degree of freedom (i.e., reduced natural frequency), but blade flap bending moments and
hub bending moments are not otherwise appreciably affected by the magnitude of yaw compliance.
The magnitude of tilt compliance has little effect on these three components of fatigue.
The tower top tilt moment is obviously most strongly affected by the softness of the tilt degree of
freedom, with increased softening of the yaw degree of freedom actually offsetting some of the
loads improvement.
Configurations with yaw frequency of
at least 0.7P are able to keep the yaw
70%
angle range within 10°, which was a
60%
stated goal. The Configurations with 50%
tilt natural frequency of 1.3P were 40%
able to keep the tilt angle within the
desired range of ±2.5° and minimized
the increase in maximum tip deflec­
30%
tion. The stiffness is considerably
10%
higher than the value originally sought 0%
for the best load isolation. A larger
yaw damper also helps to limit tilt motion.
For a given tilt natural frequency,
the tilt motion increases as the
-10%
yaw natural frequency drops. The
simulations do show an interaction
25
20%
between tilt and yaw motion. After
examining all of these simulation re­
sults, it was concluded that the stiffest 15
case (i.e., ωtilt=1.3P,ωyaw=1.2P showed
the best combination of load reduction
with minimal yaw and tilt motion.
This case is seen as the yellow bars in
Figure 8. Fatigue is reduced by 34%
Tilt and Ya w Angle Ranges [°] Reduction of Fatigue
20
10
5
ωSeries1 tilt=1.3P, ζtilt=0.3,fixed
yaw
ωSeries2 tilt=0.7P, ζtilt=0.3,fixed
yaw
ωSeries3 tilt=1.3P, ζtilt=0.3, ωyaw=1.2P, ζyaw=0.3 ωSeries4 tilt=1.3P, ζtilt=0.3, ωyaw=0.7P, ζyaw=0.3 ωSeries5 tilt=1.3P, ζtilt=0.3, ωyaw=0.4P, ζyaw=0.3 ωSeries6 tilt=0.7P, ζtilt=0.5, ωyaw=0.7P, ζyaw=0.5 ω Series7 tilt=0.7P,ζ tilt=0.3 ,ωyaw =0.4P ,ζyaw=0.3 blade flap bending tower top yaw moment tower top tilt moment hub bending moment
moment
(a) Reduction of Fatigue
for yaw moment, 35% for tilt moment, 0
0.0
6% for blade flap moment, and 14%
Tilt Angle Range Yaw Angle Range Increase in Tip Deflection
for low-speed shaft bending. The
tower clearance is reduced by 0.54m.
(b) Tilt &Yaw Angles & Tip Deflection
Figure 8. Impact of Yaw and Nodding Compliance on
As a progression from this study, a
more detailed analysis of tower top
Fatigue & Motion
flexibility was completed. This study introduced a drive train nodding degree of freedom to the
flexible blade configurations studied above.
From Figure 9, it is evident that introducing nodding freedom into the tower top has only a small
and mixed effect on most of the components for fatigue on the baseline configuration as well as
25
2.5
2.0
1.5
1.0
0.5
Increase in Maximum Tip Deflection [m]