Environmental Engineering Reference
In-Depth Information
4.6.4.1 Commentary to Table 4.4
Power production (DLC 1.1 to 1.15)
In this design situation the offshore wind turbine is in operation and connected to the
electricity grid. A conservative combination of the deterministic wind and sea state
conditions is required, which means that the phase shifts between wave crest and peak
gust are arbitrary and therefore can occur in the most unfavourable combination.
Irregular sea state conditions should be assumed for DLC 1.1 and 1.2. The wind speed
intervals within the range to be investigated (V
in
V
¼
V
hub
V
out
) may not be
selected as greater than
V
¼
2m/s. The significant wave height (H
¼
H
s
(V)), the
peak frequency of the sea state spectrum (T
p
) and the direction of movement of every
normal sea state together with the associated average wind speed (V
hub
) should be
selected on the basis of the combined long-term distribution of the wind and sea
state parameters for the location. During the design work it should be ensured that the
fatigue damage to the structure is ascertained for the complete long-term distribution of
the wind and sea state parameters (see Section 4.9).
Average wind speeds (V
in
V
hub
V
out
) and the corresponding regular waves with
significant wave heights (H
¼
H
s
(V)) should be used for DLC 1.3 to 1.13, see [11]
4.3.3.2 (6) and (7).
If no data is available regarding the probabilities of the combined occurrence of
wind and sea state or if the wind turbine classes according to Table 2.8 are to be
used, then it is possible to use the relationships between the hourly average of the wind
speed (U
¼
U
10m,1h
) and the peak frequency of the JONSWAP spectrum as well as the
significant wave height (H
s
(U)) to [11] appendix 4.E (see Section 2.5.6 and Table 2.11).
Example (equations taken from Section 2.5.6, conversion factor from Table 2.9):
Wind speed at hub height
ð
z
hub
¼
100 m
Þ :
D
s
Corresponding wind speed at 10m height above sea level:
U
10 m
;
1 h
¼
0
V
hub
¼
25 m
=
0
:
14
0
:
14
:
91
V
hub
ð
10
=
z
hub
Þ
¼
0
:
91
25
ð
10
=
100
Þ
¼
16
:
48 m
=
s
Fetch
:
x
¼ 600 km
Time
:
t
¼ 12
h
U
2
48
2
j ¼
g
x
=
¼
9
:
81
600 000
=
16
:
¼
21 672
u ¼
g
time
=
U
¼ 9
:
81 ð12 60 60Þ=
16
:
48 ¼ 25 716
0:3
3=7
n ¼ Max
:ð0
:
16
;
2
:
84 j
;
16
:
8 u
Þ¼Max
:ð0
:
16
;
0
:
141
;
0
:
216Þ¼0
:
216
Peak frequency
:
T
p
¼
U
=ð
g
nÞ¼16
:
48
=ð9
:
81 0
:
216Þ¼7
:
78
s
Significant wave height:
H
s
;
JONSWAP
¼
0
5
=
3
U
2
216
5
=
3
48
2
35 m
The average wind speeds (V
hub
¼
(V
r
or V
out
)) and either the corresponding maximum
wave heights (H
max
(V
hub
)) or the maximum 1-year wave height (H
¼
H
max,1
) should be
used for DLC 1.15. The larger values govern in each case.
:
0094
n
=
g
¼
0
:
0094
0
:
16
:
=
9
:
81
¼
3
:
