Analyses |
 
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Analyses |
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The base of each riser and tether is fixed in all translational degrees of freedom. The upper ends of the risers are attached to the vessel. The initial position of the vessel and the RAOs are also specified. The mid-water arch is fixed in all translational degrees of freedom at four corners in the initial static analysis, to allow the risers to solve statically. The arch is then released in a subsequent restart static analysis to allow the entire system to attain static equilibrium.
In this dynamic stage, a regular wave is applied to the structure. The wave amplitude is 8 metres, the period is 10 seconds and the wave direction is 45° anti-clockwise from the global Y-axis. The boundary conditions remain unchanged and are carried through automatically from the previous analysis. A variable time step is used to allow the software to use an optimal time step – this will vary over the course of analysis as the risers interact with the arch structure under the influence of wave loading.