﻿ Line data: Structure

Line data: Structure

Each line can be made up of up a number of sections with different properties, the sections being defined sequentially in the end A to end B direction.

Line type

The line type holds the data for the physical properties of the section.

Section weighting

Only available when the length and end orientations are calculated from end positions. In this case, the total length of the line is enforced to be equal to the distance between end A and end B, as defined by the line's end position data. If the line is composed of multiple sections, then this total length is split between the individual sections according to the defined section weightings. For example, a section with a weighting of 2 would be twice as long as a section with a weighting as 1, but the combined length of all the sections would always add up to the direct span between the two line ends.

Section length

The unstretched length of the section. This is the unstressed length (i.e. zero wall tension) at atmospheric pressure inside and out. Length changes due to external and internal pressure, and allowing for the Poisson ratio effect, are calculated and allowed for by OrcaFlex.

If the line type is profiled then the section length is determined by the profile data and so cannot be edited here.

Expansion factor

This factor is applied to the unstretched section length to represent, for example, thermal expansion or contraction. A constant value of ~ here has the same meaning as a value of 1: the unstretched length is unchanged.

As an alternative to a constant value, you can instead set up a variable data source, which defines a table of expansion factor against simulation time to represent time-varying changes in unstretched length. This varying multiplicative factor is applied to the unstretched length when calculating total mean axial strain, which in turn is used to calculate effective tension.

 Notes: Expansion factor is only used in the calculation of strain. It has no effect on mass, buoyancy, drag, added mass etc. The expansion factor mechanism is not intended to model line payout or haul in. This should instead be modelled using the line feeding feature. An expansion factor cannot be used in conjunction with an expansion table defined on the underlying line type. OrcaFlex only permits one or the other to be in use for a given line section.

Target segment length, number of segments

These determine the segmentation of the section.

If the target segment length is set to '~', then the number of segments in the section is set according to the number of segments.

Otherwise, the segmentation is based on the target segment length and the number of segments data item is not editable: it reports the actual number of segments used, which is calculated as (section length / target segment length) rounded to the nearest integer.

 Note: It is usually preferable to determine segmentation by defining the value of target segment length. This allows you to alter section lengths without altering their segment length.

Clash check

Clash modelling for this section is included when this data item checked. Otherwise the section will be ignored for clashing purposes.

 Notes: Line clashing is not modelled during statics. Clash checking is quite time consuming, so you should only include clash checking for those sections for which you need clashing to be enabled.

Cumulative length, cumulative segments

These columns report the cumulative length and cumulative number of segments, counting from the first section. The values are for reporting purposes only and cannot be edited.

Profile graph

The profile graph button shows a graph of the inner and outer radii of the line as they vary with arc length. This is especially useful to check that stress joint and bend stiffener data have been correctly entered.