Conversion of SIMO catenary system to RIFLEX Slender system
1. Purpose
The purpose of this converter is to assist the user in creating a new RIFLEX task from an existing SIMO catenary system.
2. Description
Converting a SIMO catenary system to a RIFLEX Slender system can be done automatically by rightclicking the Catenary System folder and choosing Convert to new RIFLEX task.
2.1. Nodes

Supernodes for fairleads and anchors are created based on the SIMO catenary system.

The initial and static coordinates of the fairlead supernodes are equal.

The static coordinates of the anchor supernodes are the same as in the SIMO catenary system.

The initial coordinate of each anchor supernode is on the seabed, in the mooring line plane, such that the mooring line initially is a straight line.
2.2. Lines

A line is created for each catenary line in the SIMO catenary system.

The lines in RIFLEX have the first end point at fairlead and the other end point at the anchor.
2.4. Cross sections
One cross section is created for each line segment in the SIMO catenary system.
2.4.1. Crosssection properties
Axisymmetric cross sections are applied.

The mass coefficient is set to \(w_{air}/g\), where \(w_{air}\) is weight in air per unit length from SIMO and \(g\) is acceleration of gravity.

The external area is set to \(w_{air}(1\text{watfac})/(\rho g)\), where \(\text{watfac}\) is the ratio between weight in water and in air and \(\rho\) is the water density.

The internal area is set to zero.

The radius of gyration is set to 0.01 m.

Default thermal/pressure expansion is applied.

Default stress calculation is applied.
2.4.2. Stiffness properties
Bar elements are applied.

Nonlinear axial stiffness is applied.

If constant axial stiffness given in the SIMO catenary system, this stiffness is used in tension and the cross section is made very soft in compression. This is a trick to improve numerical stability.

If an elongation characteristic (either stressstrain or tensionstrain) is given in the SIMO task, this characteristic is applied in the cross section.
2.4.4. Hydrodynamic force coefficients

Nondimensional coefficients are applied.

The hydrodynamic diameter is set to the segment diameter in the SIMO catenary system.

Quadratic drag in normal direction is taken from the SIMO catenary system.

Quadratic drag in tangential direction is set to \(C_t/\pi\), where \(C_t\) is tangential drag coefficient from the SIMO task.

Linear drag coefficients are set to zero.

Added mass in normal direction set to 1.

Added mass in tangential direction set to 0.
2.5. Seabed properties

The water depth is taken from the SIMO task.

The bottom tangent option is set to Seafloor contact forces on all nodes below bottom z.

The vertical stiffness is set to 50 kN/m\(^2\).

The axial friction is set to 1. This is a global parameter in RIFLEX, but not in SIMO.

All other stiffness, damping and friction parameters are set to 0.
3. Limitations

Only catenary lines with anchor position specified by global coordinates can be converted to a new RIFLEX task. Catenary lines specified with the other options can be converted to catenary lines with global anchor coordinates and then converted to a new RIFLEX task.

Buoys are not supported as the data in SIMO catenary systems is insufficient to create nodal bodies in RIFLEX.

Direct input line type is not supported.