Parameters Tab Best Practice
a.Review line lengths and distances between start/end points of a line. Convergence issues are often caused by excessive deformation or global buckling behaviour in the static analysis. Therefore, ensure no stretching or excessive curvature in the model, particularly for the sag-bend. This can be done by checking that the departure angle of the line as it leaves the stinger is less than or equal to the stinger tip angle. Note that for shallow water models where the tip close to the seabed then you may have to look at reducing the departure angle further so as to ensure sufficient tip separation for the sag-bend. The following figures illustrate the previous points.
b.Calculated seabed connection points automatically try to achieve a suitable line profile taking into account the previous points with regards to pipeline stinger departure. Therefore, for efficiency it is best to use seabed connections as much as possible. However, the calculated points may not always be ideal so a review of the provided line profile is important. If you are not satisfied with the line profile, you can manually move the calculated point (generally any required movements are small). Shallow water models are particularly sensitive with fine margins between a stable model (leading to successful convergence) and a problematic model (leading to convergence errors).
2.Avoid having excessive lengths of line on the seabed (particularly if the seabed is flat) as this results in extra unneeded elements and longer run times. Refer to the previous Line Best Practice section for guidance on ideal line lengths.
3.For scenarios where there are natural hinge points along the pipeline, for example where cables meet heavy rigid bodies, and these points tend to move suddenly downwards during the initial static step leading to instability and convergence difficulties (e.g. shallow water start-up or laydown procedures), it is worth considering using the stabilisation parameters for some of the pipe sections or cables in the model. When stabilisation is switched on for a particular component its start and end points are pinned for the initial static analysis step and are then released during a subsequent quasi-static step, after which the normal static analysis procedure takes place. This two-step process is intended to allow models to reach a fully equilibrium state before trying to perform a full static analysis sequence on them.
4.Remember that parameter changes in a particular installation stage are carried over to subsequent stages, unless you select to reset a stage on the Installation Stages tab in which case all parameter changes are removed and the original model from the Model component is considered.
5.Try to use the Automate Stages function to replicate parameter changes across a number of stages. You can always adjust the automatic parameters manually afterwards. Refer to the Installation Stages Best Practice section for more details on the Automate Stages function.
6.Remember that the list/number of available parameter types is different/smaller for restart stages than for non-restart stages.