Civil Engineering Reference
In-Depth Information
vertical velocity component are in average independent of the OWF effect on
atmospheric temperature and humidity forcing fields in 10-m height. The horizontal
velocity varies only in order of
0.001 m/s due to gradients in density fields
triggered by determined temperature and salinity changes based on the forcing
but do not affect vertical motion.
Changes in the surface elevation
in the case of scenario
B1-2030much
are
illustrated in Fig.
6.8
for all eight wind direction cases. As the theoretical analysis
implies, a dipole of
ζ
is even formed in the more realistic simulation of the German
Bight. The magnitude of dipole
'
s extrema is similar for each wind direction case
within the range of
0.382-0.0308 m. Mostly, the minima results in a stronger
effect than the increase, with the exception of wind direction cases SE, S, and
SW. The positions of dipole
ζ
s extrema depend on wind direction. Downstream
behind and within the OWF (lee of OWF), often a minimal in
'
is identified and in
front of the OWF, that is, in windward of the OWF, the maximum is detected.
Changes in the surface elevation are connected with greatest wind stress and thus
the wake in velocity components. Having
u
-component as the strongest content of
wake, the wake areas lead to an increase of
ζ
; having
v
-component as the strongest
ζ
wake, then the
-maximum occurs in the area of the
v
-component wake. That
fits with the explanations of Ekman transport and divergence and convergence in
Sect.
5.2.3
.
Therefore, two positive extrema of the
ζ
-change exist in the case of wind
direction
S
because over the OWF district, the
v
-component shows two areas of
flow reduction; see Fig.
6.11
. In the case of wind direction
W
, the
u
-component
shows in Fig.
6.10
a wake over the OWF district with three local minima that end in
three local minima at surface elevation between latitude 54
and 55
. Although
changes in surface elevation are in maximum order of 0.04 m, such a small change
can have an economic relevance for the Elbe estuary concerning shipping and
harbor industries. Here, changes of the surface elevation due to the OWF expansion
should be considered besides tides in the case of bigger ships leaving and entering
Elbe and Hamburg harbor because for these, a water-level change of a few
centimeters plays an important role in order for them not to run aground. Such a
change can also play a role in the case of storm surges.
The theoretical analysis in Chap.
5
underlines the formation of up- and
downwelling cells due to the change in surface elevation. Such cells also occur in
the German Bight (Figs.
6.7
and
6.9
). Figure
6.9
illustrates the
change of the
vertical velocity component w
at 12.5-m depth. In contrast to the two main vertical
cells in theory, here, belts of up- and downwelling occur depending on the arrange-
ment of wind farms within the EEZ.
The belts of maximal changes depend on surface elevation. In the case of a
negative change in
ζ
, upwelling is simulated, and in the case of a positive change in
ζ
, downwelling is simulated, which agree with the theoretical results. The magni-
tude of vertical motion is independent of the wind direction due to a high agreement
of extrema between wind direction cases. Maximal upwelling is 7.0
ζ
10
5
m/s
10
4
m/s (8.64 m/d).
In waters with depths of 30 m, such motion means an overturning within 3.5-5
(6.05 m/d), and the maximal downwelling has speeds of
1.0
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