Wind resources at Horns Rev

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6.3 Numerical simulations models
Prior to commencing the marine measurement programme, a numerical study was
performed. The aim of this study was primarily to establish estimates of the long-term
extremes of waves, currents, and water level. However, an important part of the study
was also to estimate the accessibility of the turbines for different limiting sea conditions
(values of Hs) and ”wave window lengths” [11].
The input for this study was a 15-year continuous meteorological data series covering
the North Sea. These meteorological data were used as input to the MIKE OSW model
(Danish Hydraulic Institute’s offshore wave model) to simulate a 15-year consecutive
wave train in the proximity of the wind farm. Since the water depth is rather limited in
and around the wind farm, the OSW waves were used as input to a shallow-water wave
model, which could then simulate the waves inside the wind farm site.
Table 6.3 lists the extreme value analysis results for 10-, 50- and 100-year return
periods.
Table 6.3 Extreme values from numerical study [11]
Parameter 10-year return period 50-year return period 100-year return period
Hs 5.0 m 5.3 m 5.4 m
Hmax 8.1 m 8.1 m 8.1 m
Currents 0.79 m/s 0.88 m/s 0.92 m/s
Water level -1.7 m / +3.0 m -2.4 m / +3.5 m -2.7 m / +3.7 m
Comparing Table 6.3 with the measured values (Table 6.2) over the 3-year measuring
period, the only divergence observed is that the measured currents exceed the long-term
predictions. However, this is fully expected as the current meter is located close to the
met mast on a water depth somewhat lower than the average water depth in the wind
farm site, which was used in the numerical simulations.
The analysis of ”wave windows” was made on a monthly basis. In Figure 6.17 the
accessibility, assuming that Hs permanently has to be below 1.3 m in time periods of 12,
24 and 72 hours, is plotted for each month. The accessibility in the winter season can be
as low as 20% whereas the summer offers an accessibility of 70–80%.
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