Analysis 02: OWF Effect on the Ocean - On the Effect of Offshore Wind Farms on the Atmosphere and Ocean Dynamics - page 109

Portugal; the Windflow Project 2012/2013 in France; the SWAY concept of
Inocean, Shell, and Statkraft; and others will result in offshore wind farms being
independent of ocean depth in the future, but such constructions are still in the
testing phase. However, companies yet prefer nonswimming fundaments, and so
they are restricted to shallow waters (BWE 2013 ). Considering a possible construc-
tion in the German EEZ, a maximum depth of 60 m, which was used in previous
analysis, must be negotiated. Common depths of areas being selected for wind
farming count around 30 m, like the depth of the area of OWF alpha ventus .
Keeping in mind that in the case of 60-m ocean depth the OWF impacts the
whole ocean, this section will clarify whether a shallower water of 30-m depth will
strengthen the OWF effect on hydrographic conditions and vertical mixing or not.
The idea behind this analysis is that a smaller vertical extent supports a stronger
vertical temperature excursion.
Analysis covers the master simulation T012ug08 TS01HD60F01 , here denoted
as HD60, and the HAMSOM run T012ug08 TS01HD30F01 , denoted as HD30. To
compare simulations based on 60-m (HD60) and 30-m (HD30) depths, the start
field of temperature-salinity stratification in the case of HD30 is in accordance with
the upper layers of run with 60 m because the TS start field is just cut at 30 m. So
distribution from top to bottom till 30 m is the same in both cases.
A comparison of the OWF effect on surface elevation in dependence on HD60
and HD30 after 1 day of simulation is pictured in Fig. 5.38 . The simulation of HD30
results in a stronger growth of the dipole effect with a difference of +2.10 10 3

10 3 m. The stronger stamped dipole in HD30 is connected with the
shallower model box setup and a more intensified wake in the flow through all
ocean layers, displayed at the velocity component u in Fig. 5.39 a1-a3.
The reduced effect at u -component between 10 and 12 m is based on a weak
reverse flow in REFr, as well as in OWFr, due to exchange processes at the
thermocline. The whole ocean depth in HD30 undergoes an average of 16.14 %
stronger reduction of the flow than HD60, considering only the upper 30 m for
HD60. Thus, wake in the velocity component u is formed quicker, which supports
an accommodation of speed between top and bottom layers and so a reinforcement
of the wake.

and 3.94

a b c

Fig. 5.38 Effect of 12-turbine OWF on surface elevation of simulation with 60 m (a), 30 m (b),
and difference of 30-60 m (c). A stronger reaction of shallower waters is illustrated. Crosses mark
the position of extrema. Horizontal black lines encase OWF district