Environmental Engineering Reference
In-Depth Information
where
T
¼
10 s gust rise time (ECG, see above)
Extreme wind shear (EWS)
The extreme wind shears with a return period of 50 years are to be considered in the
following wind speed progressions:
- For a vertical wind shear varying over time:
8
<
!
a
1
=
4
z
z
hub
z
z
hub
D
D
L
L
2
p
t
T
V
hub
þ
2
:
5
þ
0
:
2
b s
L
1
cos
Vz
ðÞ¼
;
for 0
t
T
:
a
z
z
hub
V
hub
for
t
<
0 and t
>
T
- For a horizontal wind shear varying over time:
<
!
a
1
=
4
z
z
hub
y
D
D
L
L
2
p
t
T
V
hub
þ
2
:
5
þ
0
:
2
b s
L
1
cos
Vy
ð
;
z
;
t
Þ¼
for 0
t
T
:
a
z
z
hub
V
hub
for t
<
0 and t
>
T
where
s
L
m
½
=
s
¼
I
15
ð
15 m
=
s
þ
a
V
hub
Þ=
ð
a
þ
1
Þ
Þ
ð
as for the NTM
Þ
a ¼ 0
:
2
b ¼ 6
:
4T¼ 12 s D ¼ rotor diameter
(
0
:
7 z
hub
for
z
hub
<
30 m
L
L
¼
ðas for the EOGÞ
21 m
for
z
hub
30 m
The two extreme wind shears are to be considered independently of each other and
therefore are not applied simultaneously. As an example, Figure 2.17 compares the
maximum and minimum extreme vertical wind shears. Figure 2.18 is a diagram
showing how the wind speeds change over time.
2.3.2.5 Wind farm in
uence
Offshore wind parks usually comprise multiple wind turbines (up to 200). Wind field
perturbations in the wakes of rotors must be considered in the loading assumptions,
both with respect to shielding and the reciprocal influences and superpositions. For
more information please see [11] 4.2.2.5.
