OrcaFlex Manual - Orcina

w
357
System Modelling: Data and Results, Lines
� Standard results like Effective Tension, Bend Moment, etc. are available at line ends as well as at mid-segment
points. For example to obtain the end tension at End A you can ask for the Effective Tension (or Wall Tension) at
End A.
� Magnitude and other components of the end force and end moment vectors.
� Bend Restrictor Load, which is a special end load result useful for bend restrictor design.
Sign Convention
When considering the sign of end load components the question arises as to whether the load reported is that
applied by the line to its connection or vice versa. The OrcaFlex convention is that the load reported at any point is
that applied by the B side of that point to the A side. So at End A we report the end load applied by the line to its
connection (e.g. a vessel), but at End B we report the end load applied to the line by its connection. This is in keeping
with the OrcaFlex convention for specifying the no-moment direction.
Treatment of Links and Winches attached to the end node
Normally, the end force and end moment are the total load acting between the end node and the object to which it is
connected. This includes forces from any links or winches attached to the end node.
However if the line end is free, or has been released, then it is not connected to any object. In this case the end
moment is zero and the end force is taken to be the total force acting between the line end and any links or winches
attached to the end node. If there are no attached links or winches, or they have been released, then the end force is
zero.
Standard Results
Effective Tension, Wall Tension,
Shear Force, x-Shear Force, y-Shear Force,
Bend Moment, x-Bend Moment, y-Bend Moment,
Curvature, x-Curvature, y-Curvature
These results variables are available at the line end nodes, as well as at mid-segment points. Whether you are given
end values or mid-segment values depends on the point at which you ask for the results. If you ask for these results
at EndA or EndB, or at an arc length that is closer to a line end than to the nearest mid-segment arc length, then the
values at the line end will be given. Otherwise the values for the nearest mid-segment point will be given.
For mid-segment values see Line Results: Forces, Line Results: Moments and Line Results: Pipe Stresses.
At a line end they report the components of the end loads in the local node directions of the end node, as follows:
� Effective tension is the component of the end force vector in the end node axial direction (= Nz direction).
� Wall tension is derived from the effective tension at the line end, using the pressure effects formula.
� Shear is the component of the end force vector normal to the end node axial direction.
� x-Shear and y-Shear are the components of the end force vector in the end node Nx and Ny directions.
� Torque is the component of the end moment vector in the end node axial direction.
� Bend moment is the component of the end moment vector normal to the end node axial direction.
� x-Bend Moment and y-Bend Moment are the components in the end node Nx and Ny directions.
� Stress results are based on the end load components in the end node axes directions.
Differences between End Loads and End Segment Loads
The end values of these results differ from the corresponding values for the end segment for two reasons.
Firstly, they include the loads (weight, buoyancy, drag etc.) on the last half segment adjacent to the end.
Secondly, they are components in the local node directions (Nx,Ny,Nz) at the end node, whereas the end segment
values are components with respect to the segment directions (Sx,Sy,Sz). The end node is often not aligned with the
end segment because end connection stiffness turns it towards the end orientation direction. For example:
� If the end connection stiffness is zero, or if the line end is free or has been released, then the end node directions
are aligned with the end segment directions. The end node values then differ from the end segment values only
by the loads on the end half segment.