# Line data

### Name

Used to refer to the line.

### Include torsion

Torsional effects can be included or ignored, for each line in the model. If torsion is included then the line type torsional properties must be specified.

To see the line orientation on the 3D view, you can tell OrcaFlex to draw the node axes at each node. These axes show you how the line is behaving torsionally.

 Notes: The node axes are drawn using the node pen, defined on the line data form. If torsion is included for a line, you must define the torsional orientation at each end of the line. This is done by setting the gamma angle of the end connections on the line data form. The gamma angle determines the torsional position of the line end. To check visually that you have the orientation you expect, you can draw the node axes. If torsion is included for a line, the static analysis should also include the effects of torsion – otherwise the simulation will start from a position that is not in torsional equilibrium and an unstable simulation may result. We recommend that the full statics option is selected, as this is the only line statics option in OrcaFlex that includes the effects of torsion.

### Top end

This is used to define the sense of the line. Some calculations performed by the OrcaFlex need to know which end of the line (end A or end B) is at the top, and which end is at the bottom. You specify which is at the top, and OrcaFlex assumes that the other end is at the bottom.

Suppose you have a line with the top end connected to a vessel, and the bottom end anchored to the seabed. If you wish to measure arc length from the vessel then you should connect end A to the vessel, make end B anchored and set the top end to end A. On the other hand, if you wish to measure arc length from the seabed then you should connect end B to the vessel, make end A anchored and set the top end to end B.

The top and bottom end settings are used by OrcaFlex as follows:

If the line is not in contact with the seabed then top and bottom end designations are somewhat arbitrary. You are free to make whatever choice suits your model, but remember that the contents pressure will be referenced from the top end. If the entire line is in contact with the seabed, then again you are free to make whatever choice of top and bottom ends suits your model.

### Representation

Specifies how the line should be modelled. You may choose between finite element and analytic catenary representations.

### Length and end orientations

There are two options:

• Explicit:section lengths and end orientations must be specified explicitly by the user.
• Calculated from end positions: OrcaFlex will set the section lengths and end orientations automatically from the end positions, such that the total unstretched length of the line is equal to the distance between end A and end B in reset state, and the $z$-axis of the local axes at each end will point along the straight line running from end A to end B (with the $y$-axis chosen to be horizontal). This option, together with the the section weighting and end offset data, can be used to simplify model building for truss structures.
 Note: Free constraints can be used in such truss structure models to embody the degrees of freedom at the points where several structural members meet. The calculated from end positions option cannot be used in conjunction with mid-line connections.

### P-y model

Defines (optionally – the default is none) the P-y model used to define horizontal soil loads for a vertical line that extends beneath the seabed.

### Wave calculation method

Specifies which wave calculation method will be used when computing the line's wave kinematics during the simulation. The default value is specified by environment, which means that the global method specified on the environment form will be used; this may be over-ridden for individual lines.

### Characteristic scales

For some models it may be desirable to explicitly set a characteristic length and characteristic force for the line. These characteristic scales directly affect the convergence criteria of the iterative solvers employed in the analysis. The data does not appear on the line data form but can be found on the all objects data form.