Analyses |
 
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Analyses |
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The base of each of the mooring line is fixed in all translational degrees of freedom. The CALM buoy CoG is also fixed in all degrees of freedom. A displacement of 10m is applied in the vertical or buoy heave direction at the CoG; this serves to develop tension in the mooring lines making for greater solution robustness in the next analysis stage. If the steel transfer line is included in the model, the remote end of the line is fixed in all translational degrees of freedom.
The only change here is that the heave, surge and pitch constraints are removed from the CALM buoy CoG. The system mean equilibrium position is obtained as the buoy settles under the influence of gravity and buoyancy.
There is a total of 14 dynamic analyses of each model (with and without offloading line), making 28 analyses in total. Periods range from 4s to 20s (the values in the range omitted to keep the number of total runs down are 15s, 17s and 19s). In all cases, the BCs remain unchanged and are carried through automatically from the release analysis. Each dynamic simulation is run for 10 wave periods, using a variable time-step, and a ramp time of one wave period.
As noted previously, the main variables of interest are the buoy CoG motions in heave, surge and pitch, to define buoy motion RAOs. For this reason, the Summary Postprocessing facility is invoked, to generate a summary output file containing just the required variables of interest. The CALM buoy motions in heave, surge and pitch correspond to the motions of Node 8004 in DOFs 1, 2 and 6.
Each dynamic analysis runs 10 wave periods, but in generating the summary output only the results over the last 2 wave periods are considered. Note also that the Delete Database option is invoked. The 28 dynamic analyses generate considerable database output. The Delete Database option allows you to delete the database files for each run immediately the required results are extracted by the Summary Postprocessing facility, so minimising disk usage.
The summary outputs of the dynamic analyses are collated so that the results can be viewed all at once as follows: the results where the offloading lines are present are collated separately from the results where the offloading lines are missing. This is achieved using Flexcom's Summary Collation capability. The collated results are presented in a collation spreadsheet and a 3D collation plot.