Environmental Engineering Reference
In-Depth Information
where
V
e,N
(z)
expected extreme wind speed (N
¼
50 or N
¼
1), averaged over 3 s
V
red,N
(z)
reduced extreme wind speed (N
¼
50 or N
¼
1), averaged over 60 s
b) Turbulent extreme wind model:
0
:
14
V
50
ðÞ¼
V
ref
ð
z
=
z
hub
Þ
V
1
ðÞ¼0
:
8 V
50
ðÞ
s
L
¼ 0
:
12 V
hub
where
V
N
(z) expected extreme wind speed (N
¼
50 or N
¼
1), averaged over 10 min
s
L
standard deviation for taking into account turbulence intensity
The index N stands for the return period (N
¼
50 years or N
¼
1 year).
Various general requirements must be considered for load calculations, see [11] 4.2.2.4.1
(7).
Extreme wind speeds can be converted from the 10-min average to other averaging periods
using the values given in Table 2.9.
Extreme operating gust (EOG)
The gust speed V
gustN
at hub height, with a return period of N years, is calculated as
follows for standard wind turbine classes:
s
L
V
gust
;
N
¼ b
1
þ
0
:
1
D
=L
L
where
a
þ
1
ð Þ
(as for the NTM)
L
L
turbulence scale parameter, calculated as follows:
s
L
m
½
=
s
¼
I
15
ð
15 m
=
s
þ
a
V
hub
Þ=
0
:
7
z
hub
for z
hub
<
30 m
L
L
¼
21 m
for z
hub
30 m
D rotor diameter
b
coefficient:
b¼
4.8 for N
¼
1
b¼
6.4 for N
¼
50
The change in wind speed over time for a return period of N years is determined using
the following equation:
Table 2.9 Conversion factors for wind speeds based on the 10-min average
Averaging period
1 h
10 min
1min
5 s
3 s
Factor
0.91
1.00
1.10
1.21
1.25
