OrcaFlex Manual - Orcina

w
Specifying the Position on the Line
347
System Modelling: Data and Results, Lines
For line results you need to specify the position on the line at which you want results. This is done by setting the
entries in a row in the Position table on the results form. You are then offered the Variables that are available for
the point specified by the currently-selected row.
Each row in the table specifies one point on the line. There are multiple rows in the table, so you can set up rows
specifying a number of different points of interest and then easily switch between them by choosing which row you
select. In a row that you don't want to use you can set the Node or Arc Length column to '~', meaning 'unspecified'.
Three rows in the table are dedicated to special arc lengths on the line:
� The first and last rows in the Position table are dedicated to the line's end points A and B.
� The next to last row in the table is dedicated to the Touchdown point. This is defined to be the first node on the
seabed (starting from the Top End). If the results variable selected is a segment variable (i.e. is only available at
mid-segment points) then the value reported for the touchdown point is the mid-segment valued in the segment
that precedes the Touchdown node. When there are no nodes on the seabed then the results variable is reported
as N/A (meaning 'not available') and the graph shows no value.
Arc Length and Node Columns
The Arc Length column specifies how far along the line the point is, measured from zero at End A. For information,
if you set the Arc Length column then the adjacent Node cell is set to the number of the nearest node to that arc
length.
The Node column can also be used as an alternative way of setting the arc length. You can set the Node column to
the number of a node on the line. The adjacent Arc Length cell will then be set to the arc length to that node. The
node number must be in the range 1 (the node at End A) to N+1 (the node at End B), where N is the total number of
segments in the line.
Note: The actual arc length for which line results are reported may not be exactly the specified arc
length. OrcaFlex reports results for the 'nearest appropriate' result point. See Result Points below.
R and Theta Columns
For some variables (e.g. stress components) you must also specify the position of the point within the cross section
through the specified arc length. Whenever one of these variables is selected in the Variables list, two extra
columns become visible in the Position table. These extra columns specify the polar coordinates (R,Theta) of the
point within the cross section; see the diagram in the Pipe Stress Calculation section. The R column can only be set
to either Inner or Outer, meaning the radii corresponding to the Stress ID or Stress OD respectively. Results are not
available for points between these two radii.
Clearance Results
Clearance results can be reported either as clearances from this line to all other lines or from this line to a specified
other line. You choose which of the options is used from the drop-down list labelled "Clearances are reported as
clearances from".
Result Points
OrcaFlex uses a discretised model and so results are only available at nodes, mid-segment points and line ends; we
call these points 'result points'. The available result points depend on which variable you request, they are
documented in the description of the variable.
When you ask for a variable at a specified arc length OrcaFlex gives the value for the 'nearest appropriate' result
point. The phrase 'nearest appropriate' here means that OrcaFlex considers the available result points that are in the
same section as the arc length you specified and then chooses the one that is nearest to the arc length you specified.
If you specify an arc length that is exactly at the boundary of two sections then OrcaFlex uses the section that starts
at that arc length.
OrcaFlex always labels results with the actual arc length to the result point to which they apply, so you can check to
ensure that you are getting results at the result point you want.