Environmental Engineering Reference
In-Depth Information
Fig. 2.11 Change in an extreme operating gust over time (N¼1, turbulence category A, D¼42m,
z
hub
¼30m, V
hub
¼25m/s)
8
<
for 0
t
T
3
p
t
T
2
p
t
T
V
ðÞ
0
:
37
V
gust
;
N
sin
1
cos
Vz
ðÞ¼
;
:
V
ðÞ
for t
<
0 and t
>
T
z
hu
ð Þ
a
(NWP, see above)
T period: T
¼
10.5 s for N
¼
1T
¼
14.0 s for N
¼
50
t
where V
ðÞ¼
V
hub
z
=
time
Figure 2.11 shows an example of how an extreme operating gust changes over time.
Extreme wind direction change (EDC)
The magnitude of the extreme wind direction change
u
eN
for a return period of N years
should be calculated as follows (see Figure 2.12):
s
L
180
u
e
;
N
¼b
arctan
V
hub
ð
1
þ
0
:
1
D
=L
L
Þ
where
s
L
m
=
s
½
¼
I
15
ð
15 m
=
s
þ
a
V
hub
Þ=
a
þ
1
Þ
ð
Þ
(as for the NTM)
Fig. 2.12 Example of the magnitude of the extreme wind direction change
