Analysis 02: OWF Effect on the Ocean - On the Effect of Offshore Wind Farms on the Atmosphere and Ocean Dynamics - page 80

forcing with operating wind turbines. The theoretical analysis underlines that the
first vertical cells come up triggering changes of hydrographic parameters. There-
fore, what happens to the vertical velocity due to wind farm operation is analyzed.
Offshore wind farms need special services, which can be only done in case of
stagnancy of the rotor blades. Additionally, the wind turbines have an operating
limit based on wind speed. Depending on the machine, a normal operating turbine is
working between 5 m/s and up to 25 m/s (Vestas Wind Systems 2013 ), in the case of
METRAS simulation between 2.5 and 17 m/s. The limited operation is caused by
technical limitation. Therefore, we can assume that a wind farm or single wind
turbine is not always in operating state. What will happen if we switch off turbines
for a relatively short time duration, what happens in the case of weak or strong wind
speeds, and what differences can we estimate between different wind park sizes?
Corresponding simulation for result presentation is T012ug08 TS01HD60F03.
The aim of this section is it to make a statement on how we can trigger ocean
dynamics by switching on and off wind farms. Does the effect suddenly disappear,
or is it slowly disappearing over longer time? How long will it take to bring ocean
dynamics back to reference conditions?
Therefore, three OWF operation cases are used for this analysis. An overview of
cases is given in Fig. 5.19 , including different durations of turbine rotation.
Thereby, means

no use of the rotor disc approach, but as mentioned in Sect. 3.1.2, the wind field is
affected because the frictional resistance of rotor disc is considered. Additional
'

on means the usage of rotor disc approach in METRAS; off

' ' ' '

is implemented that fully ignores the OWF existence.
Forcing is based on M_T012ug08*onoff , whose results are introduced in Sect.
4.3. The importance of forcing includes these three:

off_ref

'

a b

Fig. 5.19 Illustration (a) shows operation cases opc01, opc02, opc03 and their operating time.
Blue is nonoperating wind turbines, red is operating wind turbines, and cornflower blue marks
simulation where OWF is ignored completely. Illustration (b) shows y -section (S-N cross section)
through the OWF for analysis ( red line )