Friction coefficients data

These data are the friction coefficients for contact with either elastic solids or supports. Contact interactions are many-to-many; each elastic solid can come into contact with any number of lines and buoys, and vice versa. The situation with supports is similar, supports can have multiple supported lines, and a line can be supported by many supports. As a result, the specification of these data is more complex than that for seabed friction coefficients.

Note: Friction for contact with elastic solids or with supports is only included during the dynamic simulation, and not in statics.

The data comprise friction coefficients defined in the following tables:

Line types table

The table contains a user-defined number of rows, each containing the following data:

Line type, shape

The given friction coefficients will be used for contact between the specified shape and any node which uses the specified line type.

The line type name can also be '(all line types)'. In this case, any node in the model, irrespective of the line type it is based on, will use the given friction coefficients when in contact with the specified shape.

Similarly, and independently of the line type setting, the shape can be '(all shapes)'.

Friction coefficients

Lateral and axial friction coefficients. If the axial coefficient is set to '~' then the lateral friction coefficient is used for all directions of motion.

6D buoys table and 3D buoys table

These tables are entirely analogous to the line types table. Instead of line types, you specify 3D buoys or 6D buoys, and there is only a single friction coefficient, because buoy friction in OrcaFlex is isotropic.

Support types table

This table contains a user-defined number of rows, each containing the following data:

Support type, line

The given friction coefficients will be used for contact between the specified line and any support which uses the specified support type. Note that lines are listed in this table, whereas line types are used in the specification of friction with elastic solids.

In much the same way as the line types table above, you can give friction coefficients for '(all support types)' and/or '(all lines)'.

Friction coefficients

Lateral and axial friction coefficients. If the axial coefficient is set to '~' then the lateral friction coefficient is used for all directions of motion.

Note: Friction between lines and elastic solids or between lines and the seabed defines axial and lateral directions using the line nodes.
The axial and lateral directions for friction between lines and supports are defined by the support cylinders. Axial friction resists sliding motion along a support cylinder axis, while lateral friction resists sliding motion that would drag a line over or around a support.

How the data are interpreted

For the most part it should be clear how the data are interpreted. The exception is when multiple rows specify friction coefficients for the same elastic solid and contacting object. For example consider the table below:

Figure: Friction coefficient data for line types

If a node using 'Line type1' comes into contact with 'Shape1' then OrcaFlex has two choices for friction coefficient since this particular contact matches both rows of the table. OrcaFlex deals with this ambiguity with the rule that the more specific combination is chosen; in this case, that is the second row which specifies 'Line type1".

A row with named line type and named shape is the most specific combination and the friction coefficients from such an entry will always be chosen over any other entries.

A row with '(all line types)' and '(all shapes)' is the least specific combination and other entries will always be chosen over this.

The other possibilities are:

  1. Rows with '(all line types)' and a named shape
  2. Rows with a named line type and '(all shapes)'

OrcaFlex regards such rows as equally specific and, to avoid ambiguity, does not allow you to mix rows of type 1 and 2 in the same table. If you do so, OrcaFlex will report the error when you try to run the simulation.

Similarly for multiple rows with identical line type and shape entries, the friction coefficients are not well-defined and OrcaFlex will again report an error.

If no friction coefficients are specified for a particular combination of line type and shape then no friction will be applied to that case. For example, with the data as in the figure above, contact between nodes and any shape other than 'Shape1' will not include friction effects.

The data in the remaining tables for 6D buoys, 3D buoys and support types are interpreted in exactly the same way.