Final report for WP4.3: Enhancement of design methods ... - Upwind

UPWIND WP4: Offshore Support Structures and Foundations
4 198.8 -154.6 1628.6 -169.3 901.0 -178.2
5 824.4 -101.9 1459.6 97.8 1650.5 90.8
6 4978.5 74.3 9370.9 81.4 3483.6 89.3
The plots in Figure 8.25 and Figure 8.26 show the comparisons between first and second-order excitation
forces for surge and pitch modes respectively for three monochromatic waves considered in this study. For the
shorter waves with period equal to 5s, the second-order component is dominant relative to the first-order. For
the longer waves with periods equal to 7s and 9s, the second-order component is gradually smaller and less
dominant. For the heave mode, results for which are not shown, the first-order component is dominant relative
to the second-order for all three waves as for the OC3-Hywind platform.
Excitation Force (surge) [MN]
1.5
1
0.5
0
-0.5
-1
-1.5
Monochromatic wave (T=5 s; H=1 m)
-2
0 5 10 15
Time [s]
Excitation Force (surge) [MN]
1.5
1
0.5
0
-0.5
Monochromatic wave (T=7 s; H=2 m)
-1
0 5 10 15 20 25
Time [s]
112
Excitation Force (surge) [MN]
4
3
2
1
0
-1
-2
-3
Monochromatic wave (T=9 s; H=4 m)
-4
0 5 10 15
Time [s]
20 25 30
Figure 8.25: Comparison of first and second-order excitation forces in surge mode for three monochromatic waves for the
semi-submersible platform.
Excitation Force (pitch) [MN.m]
15
10
5
0
-5
-10
-15
Monochromatic wave (T=5 s; H=1 m)
-20
0 5 10 15
Time [s]
Excitation Force (pitch) [MN.m]
20
15
10
5
0
-5
-10
Monochromatic wave (T=7 s; H=2 m)
-15
0 5 10 15 20 25
Time [s]
Excitation Force (pitch) [MN.m]
40
30
20
10
0
-10
-20
-30
Monochromatic wave (T=9 s; H=4 m)
-40
0 5 10 15
Time [s]
20 25 30
Figure 8.26: Comparison of first and second-order excitation forces in pitch mode for three monochromatic waves for the
semi-submersible platform.
The plots in Figure 8.27 and Figure 8.28 show the comparisons between first and second-order unrestrained
motions for surge and pitch modes respectively for the three monochromatic waves considered in this study. All
motions are small, and as for the excitation forces the influence of the second-order unrestrained motions is
more important for the shorter wave with period equal to 5s in surge and pitch modes. The first-order component
is dominant for the longer waves with period equal to 7s and 9s. For the heave results, which are not
shown, the first-order motions are dominant relative to the second-order for all three waves.