OrcaFlex Manual - Orcina

System Modelling: Data and Results, Lines
Section Turn
312
w
The amount by which the track azimuth increases over this section. A positive value denotes a turn to the left, when
viewed from above, and a negative value denotes a turn to the right. A value of zero can be entered to specify a
straight track section.
Section Radius
The radius of curvature of the circular arc. The radius equals (180L)/(πT), where L is the section length and T is the
absolute value of section turn, in degrees. For straight sections (i.e. if Section Turn = 0) the radius is reported as
Infinity.
Notes: This is a reported value, not an editable data item, and is hence always shown in grey.
Section X and Y
With a profiled or sloping seabed the actual track on the seabed will have a slightly different radius
of curvature – see Laying out the Line.
The global X and Y coordinates of the end of this track section. You can either edit these X and Y coordinates
explicitly, on the line data form, or else by dragging the end point on a 3D view. If you edit X or Y then OrcaFlex fits a
circular arc (starting at the previous section's end point) through the new end point and the Section Length and
Section Turn are automatically updated to match this new arc.
Section Z
The global Z coordinate of the section end point on the seabed. This is a reported value, not an editable data item,
and is hence always shown in grey.
Section Arc Length
The total arc length to the end of the section. This is a reported value, not an editable data item, and is hence always
shown in grey.
Section Azimuth
The azimuth direction at the end of the section. This is a reported value, not an editable data item, and is hence
always shown in grey.
Track Pen
This controls how the track is drawn. You can switch between the options of drawing the track in the chosen pen
and not drawing it at all.
Laying out the Line
The track data defines a sequence of straight lines and circular arcs in the horizontal plane, which are then projected
vertically onto the seabed to define the track itself. The program then lays the line out along the track, allowing for
any As Laid Tension specified by the user on the line data form.
Because the line is modelled as a series of straight segments, when the line is laid out along a curved track it will
repeatedly 'cut corners' and so the length of line laid along a given curved track section will be slightly shorter than
the length of that section. The size of this discrepancy reduces as more segments are used.
If End A is above the seabed then the height above the seabed varies linearly between End A and the first track
section point, reaching the seabed at the end of the first track section. If the end of the last track section is reached
before all the line has been laid out, then the rest of the line is laid out in a straight line in the direction of the end of
the track.
Sloping and profiled seabeds
The track on the seabed is obtained by projecting the specified circular arcs or straight sections vertically down onto
the seabed. With a horizontal seabed this vertical projection has no effect on the shape of the track. But with a
sloping seabed the vertical projection does not preserve distances and this causes some effects that users should
note:
� The section lengths and arc lengths that appear in the prescribed starting shape data table are lengths in the
horizontal plane, i.e. before projection down onto the seabed. With a sloping seabed the true section and arc
lengths on the seabed will differ, the difference depending on the slope of the seabed. The actual arc lengths can
be obtained by running the static analysis and looking at the Full Results table for the line.