Line data: Feeding

Line feeding allows line to be dynamically introduced into or removed from the model. See the modelling line feeding topic for more details and an explanation of the terminology. The feeding data are defined independently for end A and end B on the feeding page of the line data form.

Initial arc length

The arc length of the line end in reset state, relative to end A of the full line (i.e. of the line as defined on the structure page of the line data form). The initial arc lengths of end A and end B defined here together determine the length of active line in reset state. The default value is '~', which means that the active line end and the full line end are initially coincident. If the initial arc length data are not valid, a message will be displayed at the bottom of the page giving more information.

Payout rate

The rate at which line is fed into, or out of, the active line at this end. A positive value means that line is being paid out at this line end; a negative value means that line is being hauled in. You can also define variable data to represent a time-varying feeding rate.

Apply ramp

Determines whether the defined payout rate should be ramped during the build-up period. We recommend ramping the payout rate, to avoid introducing discontinuities between statics and dynamics. It may, however, be desirable to disable the ramp in some cases, such as variable payout rate data which already account for build-up.

Control parameters

Shortest viable segment factor

The length, as a fraction of the reference unstretched length, of a new segment as it is introduced into the active line. Ideally, this should be as small as possible, in order to minimise discontinuous behaviour resulting from changing the segmentation of the line. In practice, however, very short segments can cause convergence problems, so there is a balance to be struck here. When hauling in, this value determines when segments are removed from the active line.

Use smooth growth

Determines which growth model is used to pay out or haul in. If smooth growth is enabled, then nodes are introduced and removed slowly, relative to the line end, in order to minimise any noise that may arise from adding or removing degrees of freedom. We recommend that smooth growth is enabled whenever possible. In some circumstances, however, the smooth growth model can lead to poor convergence; in such cases, you may need to disable it.