Analysis 02: OWF Effect on the Ocean - On the Effect of Offshore Wind Farms on the Atmosphere and Ocean Dynamics - page 87

elevation and vertical cells occur. In case of UG 5/8/16 m/s, vertical cells have a
dimension of 15/30/30-40 km width and clearly affect depths till 30/60/60 m.
Therefore, difference in simulations at investigation positions dominantly varies
between P

3 and P + 3 for all variables.
Correlation (COR) of results along the single points and the root mean square
difference (RMSD) are used as a statistical tool to analyze accuracy of simulation
results based on forcing of three different wind speeds. Here, RMSD is used as a
measure of the discrepancy among the three different model samples to compare
values due to different forcing cases. In the following, the effect on the ocean due to
the wind farm is examined.
All the analyses of the three sets of wind speed forcing in Sect. 5.2.2 show that a
relatively stronger wind field means already a more intense wind wake. Considering
METRAS wind turbine parameterization, the rotor thrust grows with the cube of

velocity, so in the case of higher wind speeds, turbines are able to detract more
energy out of the atmosphere and therefore wind reduction behind OWF is inten-
sified. An intense wind wake results in an intense velocity wake of the ocean
velocity u -component. Figure 5.23 documents that fact. The overall extrema of
variables mostly increase with increasing wind speeds. The strongest effect is
identified at the thermocline at 12-m depth, while at the surface, 30 m, or at the
bottom, effects are consequently smaller.
The effect of velocity component u along investigation points P

'

5to P + 5 over
the area, based on different UG speeds, has its wake at position P 0 within the OWF
and is highly correlated by 1.00 between forcing UG5 and UG8 and 0.97 between
UG5, respectively UG8, and UG16. By means of the correlation of the three
different horizontal velocity fields , it becomes clear that velocity component
v exerts a diverse impact on the velocity field. The stronger is the wind forcing,
the higher are the discrepancies. Correlations along investigation points with UG16
are only of 0.84 at the surface. Between UG5 and UG8 forcing exist little fewer
differences; 0.87 correlates them. Wake magnitudes at the surface have a linear
character, and RMSD increases with wind speed difference.
The effect of surface elevation

ζ shows a similar distribution, having a maxi-

mum at P + 1 and a minimum at P 1, with a high correlation between UG5, UG8,

and UG16; see Fig. 5.23 . Results for at investigation points have a weak root

mean square difference between the runs of different wind speeds. The stronger is
the wind forcing, the more distinctive is the extreme of

ζ

dipole structure. The
growth of extrema leads to an exponential character but cannot be specified due to
only three wind cases.
The fact that a stronger wind results in a stronger effect on the ocean surface, the
effects on vertical velocity and temperature must be consequently intensified. The
effects on vertical velocity component and hydrographic parameter , compared by
different forced wind speeds, are pictured in Fig. 5.24 . The maximal upwelling
along investigation points occurs at point P

ζ

1 for all three wind cases through all
layers. The strongest downwelling is placed at P + 1 for wind case UG5 and UG8,
while for UG16, the maximal downwelling can be found at P 0.