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Line data: Results |
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Line data: Results |
Logging of results is enabled by default, meaning that all simulation results are available for this line. If log results is disabled, simulation results will not be available for the line.
OrcaFlex stores simulation results in an efficient way, logging only a minimal set of results to the simulation file. Other results which have not been logged are then derived from the logged ones when the results are requested. This usually means that simulation files are kept to a reasonable size; we recommend that, in general, you do log results.
Should you need to reduce the size of your simulation files, then you can choose to turn off results logging for any lines for which you do not need results.
If checked, node velocities are logged directly, and velocity results are obtained from these logged values.
Otherwise, node velocities are not logged and velocity results are derived by numerically differentiating the logged position of the node with respect to time, using the central finite difference scheme.
| Note: | Directly logging velocity leads to more accurate velocity results than are obtained by numerical differentiation of position. However, logging velocity also leads to larger simulation files. If you do not need velocity results then it may be advantageous to suppress logging of velocity. Similarly, if numerical differentiation of position gives velocity to an accuracy sufficient to meet your requirements, then it may also be advantageous to suppress logging of velocity. |
If checked, node accelerations are logged directly, and acceleration results are obtained from these logged values.
Otherwise, node accelerations are not logged and acceleration results are derived by numerical differentiation. If velocity is logged, accelerations results are derived by numerically differentiating the logged velocity of the node with respect to time, using the central finite difference scheme. If neither velocity nor acceleration are logged, acceleration results are derived by numerically differentiating the logged position twice.
| Notes: | The trade off between accuracy of results and simulation file size, as discussed above for logging of velocity, applies equally to logging of acceleration. |
| Computation of velocity and acceleration results via numerical differentiation can be problematic when a node is paid out or hauled in during line feeding. This is because a node can change from an end node to a mid node (or vice versa) between time steps, which induces a sudden change in velocity. OrcaFlex mitigates this by instead using a one-sided finite difference scheme for such occurrences. This is an improvement in the case of a single numerical differentiation, but leads to repeated values in the acceleration time-history if it is computed by numerically differentiating the logged position twice. It is therefore recommended that you log at least the velocity if line feeding is in use and you require node velocity and acceleration results. |
These allow you customise the way range graphs are displayed. The arc length axis may be horizontal or vertical. The latter option would typically be used for vertical risers, for example.
Normally the axes on an OrcaFlex graph display increasing values to the right (on a horizontal axis) or upwards (vertical axis). The axis inverted options allow you to reverse these directions. Again, this is typically used for vertical risers to arrange that up and down on the riser arc length axis of the graph matches up and down in the physical environment.
Since changes to these settings are usually motivated by the physical layout of the line in question, each line in an OrcaFlex model has its own individual settings for these data. They can also be set on the results form when the range graph result type is selected.