Line setup wizard

The line setup wizard is intended principally for mooring analyses. It adjusts the configuration of multiple lines to achieve a given tension, declination or layback, specified individually for each line included. The wizard is available when the current simulation is in reset state and may be opened from the Calculation | Line setup wizard menu item.

Calculation mode

The wizard has two modes of operation: Calculate line lengths or calculate anchor positions.

The calculate line lengths mode operates by adjusting the length of the specified section of each included line until the target value is achieved. As this mode changes the section length, we recommend that you specify the segmentation by target segment length rather than number of segments. In this way, if the wizard lengthens the line, then more segments are added automatically to maintain the target segment length.

The calculate anchor positions mode adjusts the bottom end position of each included line until the target value is achieved. The bottom end position is constrained to be along a line in the lay azimuth direction, so you must set this value for each included line before using the wizard.

To use the wizard you must tell it which lines to configure, and define a target variable and value for each.

Include this line determines which lines are included in the calculation. The wizard presents a list of all lines in the model, allowing you to exclude certain of them. For example, you may be modelling both moorings and flow lines and wish to include only the moorings.

The target variable may, separately for each line, be one of the following:

• Tension.
• Horizontal end force.
• Declination.
• Layback, defined to be the horizontal component of distance between the top end of the line and the touchdown point.
• No target, which means that the line will be included in the statics calculation but that its data are not to be modified. This is particularly useful if you are analysing buoyed systems where the upper and lower catenaries are modelled with different lines.

Having chosen a target variable (other than no target), you define a corresponding target value.

For the tension and declination targets, you must also define where on the line the target variable is calculated, using the line end and arc length fields. The arc length is measured from the given line end. For the horizontal end force target, you need specify only the line end, either end A or end B.

Line section to be modified

Specifies which section of the line is to have its length adjusted in the calculate line lengths mode.

Convergence parameters

The wizard performs an iterative calculation, and these parameters can be useful to help convergence in difficult cases.

The calculation is abandoned if convergence has not been achieved after the number of steps specified by max iterations. Sometimes, simply increasing this limit may be enough.

The non-dimensional tolerance parameter determines when the calculation is deemed to have converged. Convergence is achieved when the appropriate conditions among the following are satisfied:

• $|\text{calculated value} - \text{target value}| \lt \text{tolerance}\times F_\textrm{char}$, for tension and end force targets, where $F_\textrm{char}$ for each line is the total dry weight of the line
• $|\text{calculated value} - \text{target value}| \lt \text{tolerance}$, for declination targets
• $|\text{calculated value} - \text{target value}| \lt \text{tolerance}\times \text{target value}$, for a layback target

Changing the min damping and max damping parameters may sometimes help to help difficult problems converge. If necessary, try increasing the min damping factor to a value in the range 1.5 to 10, and/or increase the max damping factor to something in the range 10 to 100, say.

Automation

The line setup wizard can be executed in automated fashion either through the InvokeLineSetupWizard batch script command or from the OrcaFlex programming interface.