﻿ Line results: Positions

# Line results: Positions

### X, Y and Z

Available at nodes. The global coordinates of the selected node.

### Dynamic x, dynamic y and dynamic z

Available at nodes. The position of the node, relative to the static position of the node, and with respect to the static orientation of the node. By static position and static orientation we mean the position and orientation in the model's static state. So, if $\vec{p}_\textrm{inst}$ is the instantaneous position, and $\vec{p}_\textrm{static}$ is the static position, then these results report the components of $\vec{p}_\textrm{inst} - \vec{p}_\textrm{static}$ with respect to the node's static axis directions.

### Layback

Available at nodes. The horizontal component of distance between the selected node and the touchdown point.

Layback is not defined (N/A) if there is no touchdown point, that is if there are no nodes on the seabed. Likewise, if the selected node is beyond the touchdown point, then layback is not defined.

### Transverse VIV offset

Available only at nodes that use one of the time domain VIV models. This is the node's offset from the non-VIV node position, in the transverse VIV direction.

### Estimated transverse A/D

Available only at nodes that use one of the time domain VIV models. The amplitude of the oscillation in the transverse VIV direction divided by the node's VIV diameter.

### Arc length

Available at nodes. The arc length from end A to the selected point. This is generally only useful for the touchdown point, since for other points it is constant. For the touchdown point it gives the arc length from end A to the first node on the seabed, or N/A (not available) if there is no touchdown.

 Notes: This result is not available for lines that use line feeding or are partly inactive. For such lines, it is superseded by a set of more specific line feeding results.

### Expansion factor

Available at mid-segments. The expansion factor of the selected segment.

## Line feeding results

These result are only available for lines that use line feeding or are partly inactive.

### Segment unstretched length

The instantaneous length of the line segment. Most segments have an unstretched length that is equal to their reference unstretched length, but segments near a feeding line end may be smaller (or occasionally slightly larger) than their reference lengths as line is paid out or hauled in.

### Reference arc length

The reference arc length of the node as defined on the structure page of the line data form. This value remains constant for all nodes whilst they are active, and merely serves as a label for purposes of referencing points on a line in a discretisation-independent manner (e.g. when requesting results).

### Actual arc length

The instantaneous arc length of the node reported relative to end A of the full line defined on the structure page. This reflects how the line grows and shrinks as line is paid out or hauled in. For a node that is at end A or end B of the active line at the start of the simulation, this result will take a value equal to the corresponding user-specified initial arc length value defined on the feeding page of the line data form. The actual arc length is used to keep track of where the active line nodes sit relative to the full limiting line.

### Active arc length

The instantaneous arc length of the node relative to end A of the active line. This result only depends upon the portion of the line that is active – and therefore visible in the 3D view – at the given instant. It will always be equal to zero at end A of the active line.

 Notes: The reference arc length, actual arc length and active arc length are all equivalent to the standard concept of arc length for lines that do not use line feeding and are not partly or wholly inactive.