Civil Engineering Reference
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wind speeds. The direction of the geostrophic wind is west and following the
Ekman spiral; wind direction in 10-m height is southwest.
The whole simulation time for METRAS runs was counted 4 h. After 4 h, the
simulated wind wake was defined as stable in METRAS. Thus, the last time step of
METRAS result was used as forcing for HAMSOM.
Within atmosphere box simulations, METRAS runs comprise ten specified
simulations. As mentioned, they differ in the amount of turbines and predetermined
geostrophic wind. The specification of METRAS simulations, which produce
forcing for HAMSOM, is listed and explained in Table 3.2 . Simulations were
done with operating wind turbines (OWFr) and without an OWF (REFr).
Additionally, a run including different durations of wind turbine operation was
simulated; it means turbines were switched off and on. Operating wind turbines
means the use of METRAS wind turbines parameterization. Details of the operation
time are given in Chap. 4 . That simulation is used to determine the evolution of the
wind wake. To analyze the alternating OWF effect on the ocean, HAMSOM was
forced with 10-min mean wind fields and not with a constant wind field over time,
like in all other ocean simulations under TOS-01.
HAMSOM (Ocean Box Simulations)
Like in METRAS, the horizontal resolution of the ocean box in HAMSOM is
approximately 3 km
1.5 0 . In the vertical, HAMSOM
was run with two different ocean depths of 60 and 30 m. Vertical resolution is
equally spaced from ocean surface to ocean bottom by 2 m. An ocean depth of 60 m
is the maximal depth of Germany
3 km, more precisely 2.5 0
s EEZ where OWFs can be built. Also, 60 m is
listed as a limit for OWF constructions [common statement of wind industry (Dena
2013 )]. A depth of 30 m was implemented because the offshore wind farm alpha
ventus was built in such a depth.
'
Time resolution counts 1 min. The simulation time comprises 5 days in sum,
with the exception of one run that lasted over 30 days. Three days of each
simulation are spent to spin-up the ocean and 2 days to establish the OWF
s effect
'
(Fig. 3.4 ).
The spin-up is requested to avoid wind-driven waves, Langmuir circulation,
strong disruption at borders, and other implications initiated by a sudden strong
wind forcing on a reposing ocean. During the 3 days, the wind speed increases from
0.0 to 6.0 m/s for the wind component u in x -direction and from 0.0 to 2.0 m/s for
the wind component v in y -direction following a tangens hyperbolicus function.
After 3 days, spin-up time for HAMSOM is forced by METRAS over 2 days every
10 min.
Boundaries of the ocean box are treated as open, which means that boundaries
are defined according to the dynamical boundary equation.
Hydrographic starting conditions, of the temperature and salinity fields, are
defined according to different possible conditions of the North Sea. Setup for
ocean simulations under ocean box simulations comprises three different stratifi-
cations of ocean, TS01, TS02, and TS03. All three start fields of temperature and
salinity are depicted in Fig. 3.5 .
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