Mooring line

General

Model type


Options:

Lines (nonlinear) (default):

The mooring lines are modelled as actual lines

Springs (linear):

Mooring lines are modeled as linear springs in three directions

Load-displacement curve:

Uses a pre-calculated load-displacement curve and applies the corresponding horizontal and vertical force for the current displacement.

Load-displacement curve

The load-displacement curve table, which is used when Model type is set to Load-displacement curve. To extract a load-displacement curve from a mooring system, click the Extract mooring line load-displacement curve button on the Mooring system.


  • Default value:
  • Unit: —

Equivalent horizontal stiffness

The equivalent linear horizontal spring stiffness of the mooring line. This value is used if the Model type is set to Springs (linear). In addition, this value is used when performing a static equlibrium step before the time simulation, as the Model type will always be overridden to Springs (linear).


  • Default value: 100000
  • Unit: ${\text{N}} \over {\text{m}}$
  • Range: -1e+30 — 1e+23

Equivalent vertical stiffness

The equivalent linear vertical spring stiffness of the mooring line. This value is used if the Model type is set to Springs (linear). In addition, this value is used when performing a static equlibrium step before the time simulation, as the Model type will always be overridden to Springs (linear).


  • Default value: 0
  • Unit: ${\text{N}} \over {\text{m}}$
  • Range: -1e+30 — 1e+23

Yaw spring stiffness

A spring that prevents a yawing motion of the platform with this stiffness will be connected to the fairlead. Since the mooring lines (currently) don't provide any resistance to a yawing motion (for small displacements), this resistance can be included with this spring.

  • Default value: 3.278e+06
  • Unit: ${\text{N}\cdot\text{m}} \over {\text{rad}}$
  • Range: -∞ — ∞

Layout along seabed

If enabled, the segment of the mooring line that would end up below the seabed floor for a catenary shape will be laid along the seabed.

  • Default value: true
  • Unit: —

Mooring line data source

Dummy parameter, must be edited by somebody who implemented it.


Options:

From file:

Choose a file.

From parameters (default):

From parameters.

Layout

Layout of the mooring line. Should NEVER be seen by USER!


Options:

User defined:

You define the layout.

Auto (default):

The layout is automatically defined.

Geometry

Relative azimuth angle

The azimuth angle of the mooring line relative to the principal angle of the mooring system. A positive angle changes the direction of the line in the clock-wise direction (looking down on the platform).

  • Default value: 0
  • Unit: $°$
  • Range: -180 — 360

Line diameter

The diameter of the line.

  • Default value: 0.09
  • Unit: $\text{m}$
  • Range: 0.001 — 1e+16

Length scheme

The length of the mooring line can be set.

Options:

Relative length (default):

Will set the length to a factor multiplied with the distance between the fairlead and the anchor point.

Absolute length:

The length of the line is set to a specified value. Currently the length must be equal to or greater than the distance between the fairlead and the anchor (i.e. pre-tensioned lines aren't supported yet.)

Line length

The unstretched length of each of the mooring lines. This value should be greater than the distance from the fairleads to the anchor. The initial shape of the lines will be set to a catenary shape.

  • Default value: 902.2
  • Unit: $\text{m}$
  • Range: 0.001 — 1e+16

Length factor

The length of the line will be set to the shortest possible length multiplied by this factor.

  • Default value: 1.021
  • Unit: —
  • Range: 1 — 10

Anchor distance

The horizontal distance outwards from the center of the column where the line is attatched to the anchor.

  • Default value: 853.87
  • Unit: $\text{m}$
  • Range: 0.001 — 1e+16

Anchor depth

The depth from the mean sea level to the anchor support.

  • Default value: 320
  • Unit: $\text{m}$
  • Range: 0.001 — 1e+16

Fairlead center distance

The distance from the centerline of the column to the fairleads. This distance will be set to the radius of the column section by default.

  • Default value: 0
  • Unit: —
  • Range: 0 — 1e+12

Number of elements

The number of elements in the line.

  • Default value: 30
  • Unit: —
  • Range: 1 — 1000

Fairleads

Crowfoot

Enables a crowfoot mechanism between the platform and the mooring lines. Such a mechanism will give a restoring moment preventing a yawing motion of the floater.

  • Default value: 0
  • Unit: —

Spread angle

The angle in the horizontal plane between the direction outwards towards the mooring line, and the direction from the platform column's center point to the fairlead connection. For example, an angle of 90 degrees will put the fairleads on their opposite side of the column.

  • Default value: 45
  • Unit: $°$
  • Range: -∞ — ∞

Line distance

The distance (along the line) from the fairleads to the start of the mooring lines.

  • Default value: 50
  • Unit: $\text{m}$
  • Range: 1e-06 — ∞

Diameter

The diameter of the crowfoot elements, which will be modeled with a solid cross section.


  • Default value: 0.2
  • Unit: $\text{m}$
  • Range: 1e-06 — 1e+16

Number of elements

The number of elements from the fairlead to the start of the mooring line.

  • Default value: 4
  • Unit: —
  • Range: 1 — ∞

Crowfoot material

The material used for the crowfoot structure.


  • Default value: InfStiffMassless
  • Unit: —

Material

Distributed mass

The mass per unit length of the line.

  • Default value: 77.7066
  • Unit: ${\text{kg}} \over {\text{m}}$
  • Range: 0.001 — 1e+16

Elastic modulus

The elastic modulus of the line material.

  • Default value: 1.8975e+11
  • Unit: $\text{Pa}$
  • Range: 0.001 — 1e+16

Advanced

Torsional spring constant

Since the elements of the mooring line are free to rotate independently of eachother (also about their own axis), springs that prevent rotation about the element axes can be added to improve numerical stability. This constant determines the spring constant of these springs (given per unit length).

  • Default value: 0
  • Unit: ${\text{N}} \over {\text{rad}}$
  • Range: 0 — 1e+12

Constrain sideways motion

For debugging purposes. If enabled, sideways (i.e sway) motion is constrained. This allows a static analysis to be performed with only a single mooring line.


  • Default value: False
  • Unit: —