Environmental Engineering Reference
In-Depth Information
Tidal current
A power law equation is used for the velocity depending on the depth:
1 = 7
d þ z
d
U c ; sub ðÞ¼ U c ; sub
where
U c,sub velocity of tidal current at still water level (z ¼ 0)
Essentially reliable measurements are available for the tidal currents of various sea
areas.
Wind-generated current
A linear function is used for the velocity depending on the depth:
for
8
<
:
d 0 þ z
d 0
U c ; wind
d 0 z 0
U c ; wind ðÞ¼
0
for
z
< d 0
d 0 ¼ 20 m
U c;wind ¼ 0
:
015 u 10 m;1h
where
U c,wind velocity of wind-generated current at still water level (z ¼ 0)
u 10 m,1 h wind speed at height of 10m above still water level, averaged over 1 h
Figure 2.19 shows an example of the superposition of a wind-generated current and a
tidal current.
Wave-generated current
Surf-generated currents must be considered when an offshore wind turbine is to be
erected in the vicinity of a surf zone. The surf-generated current can be estimated with
the help of numerical models, for example the Boussinesq model. A simplification for
Fig. 2.19 Velocity pro les for a sea current (wind-generated, tidal and total)
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