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

UPWIND WP4: Offshore Support Structures and Foundations
unrestrained motion (surge) [m]
0.05
0
-0.05
0 10 20 30 40 50
Time [s]
unrestrained motion (heave) [m]
0.08
0.06
0.04
0.02
0
-0.02
-0.04
-0.06
-0.08
0 10 20 30 40 50
Time [s]
108
unrestrained motion (pitch) [deg]
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
0 10 20 30 40 50
Time [s]
Figure 8.18: First and second-order unrestrained motions in surge, heave and pitch modes for the OC3-Hywind for a Pierson-Moskowitz
spectrum with Hs=2.5 m (Tp=7.9 s).
Pierson-Moskowitz spectrum with Hs=5.0 m.
The comparisons of first and second-order excitation forces in surge, heave and pitch mode for the OC3-
Hywind associated with this Pierson Moskowitz spectrum (Hs=5.0 m) are shown in Figure 8.19. For this spectrum
the influence of the second-order components is of the same order of magnitude as the first-order for the
three modes and due to the higher frequency components the second-order excitation force, the total force
shows shaper peaks when compared to the first-order excitation force.
Excitation Force (heave) [MN]
1
0.5
0
-0.5
-1
0 20 40 60
Time [s]
80 100 120
Excitation Force (surge) [MN]
4
3
2
1
0
-1
-2
-3
-4
0 20 40 60
Time [s]
80 100 120
Excitation Force (pitch) [MN.m]
300
200
100
0
-100
-200
-300
0 20 40 60
Time [s]
80 100 120
Figure 8.19: First and second-order excitation forces in surge, heave and pitch modes of the OC3-Hywind for a Pierson-
Moskowitz spectrum with Hs=5.0 m (Tp = 11.18 s).
The comparisons of the first and second-order unrestrained motions of the OC3-Hywind in surge, heave and
pitch associated with this spectrum are shown in Figure 8.20. The plots show a maximum amplitude value of
about 3m in surge, 1m in heave and 13deg in pitch. The influence of second-order unrestrained motions in
surge and pitch are small, but dominant in heave when compared to the first-order motions.