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Line results: Contact |
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Line results: Contact |
The results selection form lets you choose how to report clearances:
In the text below we refer to the other lines used in the clearance calculations as the clearance lines, be they all other lines or a single specified other line.
Some lines are not available for clearance results, and some pairs of lines are not considered when calculating clearance:
In all of these cases, clearance results may still be reported, but the lines and pairs of lines listed above will not be considered when calculating these clearance results. For instance, consider a model with both analytic catenary representation and finite element representation lines. Clearance results from the finite element representation lines to all other lines will be reported, but will not account for the analytic catenary representation lines. Similarly, consider a model with some, but not all, lines included in statics. Static state clearance results are available for the lines which are included in statics, but will not account for the lines which are not included in statics.
Available at mid-segment points and line ends. These line clearance results report shortest distances between the segment or line end and the segments of other lines in the model. These distances are the shortest distance between centrelines (line centreline clearance) and the shortest distance between outer edges (line clearance).
Line centreline clearance reports the centreline clearance from the selected line to the clearance lines. More precisely, the clearance reported for a segment is the shortest distance from the centreline of the segment to the centreline of any segment on the clearance lines. Note that the clearance reported therefore does not allow for the radii of the lines involved. When clearance is reported for a line end it reports the shortest distance from the centreline of the point at the end node to the centreline of any segment on the clearance lines.
Line clearance is similar but it reports the clearance between line outer edges, allowing for their outer contact diameters.
| Note: | Line clearance can report negative values. This means that the segments in question are penetrating each other. If clashing is being modelled for both segments then a clash force will result from this penetration. |
The line clearance results are useful for checking for clashing between lines. They are available in both range graph and time history form. The range graph, for a given period of the simulation, enables you to see where on the line clashing may be a problem. You can then examine the time history of line clearance for that point on the line, to see when closest approach occurs. You can then use the replay to determine which other line is coming closest.
It is sometimes worth choosing carefully which line to check for clearance. An example is checking for clashing between a single mooring line and one or more of a number of closely spaced flowlines. Let us assume that you are reporting clearances from all other lines. The clearance graphs for the flowlines will include clearance to the other flowlines, between which clashing may not be a concern. The mooring line clearance is probably more useful, since it only includes clearance to the flowlines.
Line clearance only checks against other lines, not against edges of vessels, buoys, etc. However you can check clearance against part of a vessel (for example) by connecting a dummy single-segment line to the vessel, spanning across the area of interest. The line clearance graphs for that dummy line will then show how close other lines come to that area of the vessel.
Available at mid-segment points and line ends. As above, the results selection form lets you choose to report clearances to all other lines or to a specified other line; again, we refer to the other lines used in the clearance calculations as the clearance lines, be they all other lines or a single specified other line.
Line horizontal centreline clearance is essentially the same as centreline clearance, except that all coordinates are projected onto a horizontal plane before the calculation is performed.
Line vertical centreline clearance is the vertical distance between the two points that determine the horizontal clearance. Positive values mean that this line is above the other lines. Negative values mean that this line is below the other lines.
| Notes: | For mid-segment result points the segment used is the one containing the selected arc length. |
| Line clearance results are only available if there are at least 2 lines in the model. |
| Warning: | For complex models, building and updating clearance graphs can be slow. Having "live" clearance graphs open while a simulation is running can significantly slow down the calculation. |
The above clearance results can also be reported for the whole line as opposed to at a specific point on the line. Consequently the selected position on the line is ignored for whole line clearance results. Because whole line clearance results consider the entire line, they are not available as range graphs.
Whole line centreline clearance reports the minimum, taken over all points on the line, of line centreline clearance. Whole line clearance and whole line horizontal centreline clearance are defined analogously.
The vertical distance between the two points that determine the whole line horizontal centreline clearance. Positive values mean that this line is above the other lines. Negative values mean that this line is below the other lines.
| Note: | In addition to the results documented here, OrcaFlex also provides a line clashing report. |
Clashing results are only available if clash checking has been included for the lines concerned.
Available at mid-segment points. The magnitude of the clash force between this segment and other lines.
Line clash force is reported for the segment containing the selected arc length. Results are available in the form of time histories and range graphs. If multiple clashes occur simultaneously on the same segment then the value reported is the magnitude of the vector sum of the clash forces involved.
Available at mid-segment points. The integral of line clash force with respect to time.
Available at mid-segment points. Clash energy is calculated by integrating the magnitude of clash force with respect to depth of penetration. The contact between two segments is represented by a notional spring-damper; the clash energy then is the potential energy stored in the spring-damper.
If multiple clashes occur simultaneously on the same segment then the value reported is the sum of all individual clash energies between this segment and other segments.
Available at nodes. Line contact force is the magnitude of the total force per unit length, due to line contact with any of the lines in the model with which the selected line has a line contact relationship. Line contact x force, line contact y force and line contact z force are the components of that line contact force in the axes directions of the node at the result point.
Available at nodes. The magnitude of the total force per unit length, due to contact with any of the elastic solids in the model.
Available at nodes. The clearance is the shortest distance between the node at the result point and any point on the seabed, allowing for the outer contact diameter. A negative value indicates that the node is in contact with the seabed.
This result is not available for 3D seabeds because, for that case, it is difficult to calculate. Instead you should use the vertical seabed clearance result.
Available at nodes. The clearance is the vertical distance between the node at the result point and the seabed, allowing for the outer contact diameter. A negative value indicates that the node is in contact with the seabed.
Available at nodes. The component of seabed penetration normal to the seabed, divided by the outer contact diameter.
Available at nodes. Seabed normal resistance is the component of seabed resistance normal to the seabed, where seabed resistance means the seabed reaction force per unit length of line. Seabed normal resistance/D is the seabed normal resistance divided by the outer contact diameter.
The forces due to both seabed stiffness and seabed damping are included.
| Warnings: | The reported damping force depends upon node velocity. If this is derived by numerically differentiating the logged positions of the node with respect to time, the accuracy of the results will depend on the log sample interval. |
| Seabed resistance results from interaction with a linear seabed are reported without taking into account possible containment arising from participation in line contact. For more details, see the containment scaling section of the line contact documentation. |
Available at nodes. The magnitude of deflection and resistance of the P-y model at the node.