Analyses |
 
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Analyses |
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The base of the riser is fixed in all translational degrees of freedom, while the upper end is attached in all DOFs to the vessel with a hangoff angle of 7°. The initial position of the vessel is specified with an undisplaced orientation of 0° to the global Y-axis in the YZ plane. The vessel RAOs are also input.
The only change here is that a vessel offset of 24.8 m is applied in the horizontal (DOF 2) direction. The offset is ramped on over ten increments. All of the BCs are unchanged and carry through automatically from the initial static analysis.
A piecewise-linear current is applied to the riser, varying from 1.2m/s at the MWL to 0m/s at the mudline. The current direction is from PLEM to vessel. The BCs remain unchanged and are carried through automatically from the offset analysis.
A regular wave of amplitude 5m and period 14s is specified. The analysis is run for 4 wave periods, with results from the last period used to generate response statistics. The BCs remain unchanged and are carried through automatically from the current analysis. Since vessel BCs and RAO data have previously been input, dynamic motions are automatically applied with the onset of wave loading.
As noted in the Model Summary Section earlier, a sensitivity study is performed on dynamic analysis time-step. The base case value used is 0.01s, and analyses are also performed with step values of 0.02s, 0.04s, and 0.005s. The sensitivity study is facilitated via the Keyword Based Variations feature, which allows several variations of the base case input file to be produced automatically.