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

UPWIND WP4: Offshore Support Structures and Foundations
unrestrained motion (roll) [deg]
unrestrained motion (surge) [m]
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
0 10 20 30 40 50
Time [s]
0.15
0.1
0.05
0
-0.05
-0.1
-0.15
-0.2
0 10 20 30 40 50
Time [s]
unrestrained motion (sway) [m]
unrestrained motion (pitch) [deg]
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]
0.2
0.15
0.1
0.05
0
-0.05
-0.1
-0.15
-0.2
0 10 20 30 40 50
Time [s]
116
unrestrained motion (heave) [m]
unrestrained motion (yaw) [deg]
0.06
0.04
0.02
0
-0.02
-0.04
-0.06
0 10 20 30 40 50
Time [s]
0.5
0
-0.5
0 10 20 30 40 50
Time [s]
Figure 8.32: Comparisons between first and second-order unrestrained motions for the semi-submersible platform for a
Pierson-Moskowitz spectrum with Hs=2.5 m (Tp=7.9 s).
Pierson-Moskowitz spectrum with Hs=5.0 m
The comparisons between first and second-order excitation forces in the six modes of motion (surge, sway,
heave, roll, pitch and yaw) for the semi-submersible platform associated with this spectrum are presented in
Figure 8.33. For surge, roll, pitch and yaw, the second-order effects are important when compared with firstorder.
In sway the second-order excitation force is dominant and in heave the contribution from the secondorder
excitation force is small.
The comparisons of first and second-order unrestrained motions in the six modes of motion for this spectrum
are shown in Figure 8.34. The unrestrained motions are small in all modes. Slow drift motions can be observed
in surge, sway and yaw. The second-order unrestrained motions are of the same importance as the first-order
for roll and pitch motions and are dominant in sway. In heave the effects of second-order motions are small
when compared to first-order.
Excitation Force (surge) [MN]
8
6
4
2
0
-2
-4
-6
-8
0 20 40 60
Time [s]
80 100 120
Excitation Force (sway) [MN]
3
2
1
0
-1
-2
-3
-4
0 20 40 60
Time [s]
80 100 120
Excitation Force (heave) [MN]
1.5
1
0.5
0
-0.5
-1
-1.5
0 20 40 60
Time [s]
80 100 120