Analysis 02: OWF Effect on the Ocean - On the Effect of Offshore Wind Farms on the Atmosphere and Ocean Dynamics - page 84

Fig. 5.22 Hovm¨ ller diagrams of OWF effect (OWFr-REFr) in 12-m depths of vertical velocity
component w (a1-c1) and temperature (a2-c2) along the S-N section for the three OWF operation
cases opc01 (a1-a2), opc02 (b1-b2), and opc03 (c1-c2). Inertial oscillation is obviously seen at
w -component

As mentioned, the strongest difference, compared to theoretical run, with con-
stant forcing over time is detected at vertical velocity component w (Fig. 5.20 ). One
can expect that turning on an off wind turbines will lead to variation in the
horizontal velocity field which affect surface elevation and the vertical motion.
But the dynamic is not only pulsing; related to OWF operation, an additional side
effect occurs.
Shifted by time, the velocity component relatively strongly increases by turning
off the OWF after 4.2 h in all three operation cases.
The diversity between increase and decrease of horizontal velocity components
due to the OWF operation ends in a pulsing of vertical cells, which rotates counter
clockwise around the OWF. With time, the core of upwelling/downwelling rotates
around the OWF, which leads to the alternating trend with time. The rotating effect
only strongly affects an area

30 km around the OWF center and affects all depths.
Such alternating of velocity triggers the increase and decrease of the surface
elevation. The rotation of the vertical cells occurs due to a provoked inertial
oscillation by turning on and off the wind turbines. The movement of vertical
cells is counterclockwise, with a period of 13-15 h, which agrees with a mean
inertial oscillation T around the 55.00 latitude of 14 h based on

2 ˀ

T ¼ ð 5 : 8 Þ

2 ʩ sin ˆ

Due to no coasts and no tides in the model ocean box, the inertial oscillation cannot
be suppressed like in nature.