Analyses |
 
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Analyses |
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The bases of each of the mooring lines are fixed in all translational degrees of freedom. The steel transfer line included in the model has the remote end fixed in all translational degrees of freedom. The floating body CoG node is also fixed in all degrees of freedom. A displacement of 12m is applied in the vertical or floating body heave direction at the CoG; this serves to develop tension in the mooring lines making for greater solution robustness in the next analysis stage.
The only change here is that all the floating body degrees of freedom are now released. The system mean equilibrium position is obtained as the buoy settles under the influence of gravity, buoyancy and the static forces exerted by the mooring and offloading lines.
There are a total of 22 regular wave dynamic analyses for this model (11 each for the time and frequency domain). Periods range from 6s to 20s. In all cases, the boundary conditions remain unchanged and are carried through automatically from the release analysis. Each time domain dynamic simulation is run for 250s with a time step of 0.1s, and a ramp time of two wave periods. {For efficiency, only the 8s wave period input file is included, but you can easily recreate any of the others if you so wish}. The principal variables of interest are the floating body centre of gravity motions in heave, surge and pitch. In the time domain the RAO amplitude is based on the response over the last five wave periods.
Two random sea analyses are performed, one each in the time and frequency domain. A Pierson-Moskowitz spectrum is used, with a significant wave height of 1.5m and a mean zero up crossing period of 10s. Purely for efficiency reasons, the time domain simulation is analysed for ¼ hour only, whereas a 3 hour simulation would generally be considered recommended practice.