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)