Wind resources at Horns Rev

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energy. environment. knowledge. Page 60 of 69 Figure 6.15 Measured current magnitudes [m/s] and flow directions [°], July 1999 to December 2000 Current profiles are shown in Figure 6.16. The blue line (WL) is the mean water level for the sample period of 15 min. waves on the surface results in the variation of the profile above the read line (maxbin). The workhorse can only make valid measurements approximately 1.5 m above its position at the seabed. Valid measurements are shown in Figure 6.16 from the red line to level -5.5 m. 21.07.99 20:16 N E WL Maxbin 2 1 0 -1 -2 -3 -4 -5 -6 -7 -600 -300 0 300 600 21.07.99 17:16 N E WL Maxbin 2 1 0 -1 -2 -3 -4 -5 -6 -7 -600 -300 0 300 600 Figure 6.16 Plot of current profiles on July 21, 1999. X-axis Current [mm/s] Y-axis level [m] 0 0.2 0.4 0.6 0.8 1 Report no.: D-160949 Tech-wise A/S is an international consulting Tech-wise A/S engineering company specialised Kraftværksvej 53 in energy and environment DK-7000 Fredericia
energy. environment. knowledge. Page 61 of 69 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%. Report no.: D-160949 Tech-wise A/S is an international consulting Tech-wise A/S engineering company specialised Kraftværksvej 53 in energy and environment DK-7000 Fredericia
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