Fibre rope wizard

Depending on the input the wizard will generate either a Fibre Rope or an Axisymmetric cross-section.

The different options are

  • Default

    • This will create the default Fibre Rope cross section with no additional input

  • Different options for polyester rope:

    • Linear

    • Bilinear

    • Syrope

Input:

  • Rope diameter in mm: d

1. Cross-section properties

  • Mass coefficient: \(m_{coeff}=m_{air}\)

  • Weight in air (dry mass): The mass is calculated based on the regression line equation fitted to Bridon Superline Polyester for Permanent Mooring (Bridon fibre rope catalogue). \(m_{air}=0.0007 d^2-0.0088d+0.489\) [kg/m],

  • External cross sectional area:

\[A_{ext}=\frac{1}{\rho_{sw}} m_{air} (1-r_{air}^{sub})\\ \rho_{sw}= 1025 kg/m^3\\ r^{sub}_{air}=\frac{m_{sub}}{m_{air}}=0.25\\\]

where \(r^{sub}_{air}\) is the ratio between submerged weight to weight in air (dry mass).

2. Capacity properties

The MBL is calculated based on the regression line equation fitted to Bridon Superline Polyester for Permanent Mooring (Bridon fibre rope catalogue).

  • Tension capacity: \(MBL=0.2658d^2+4.9392d-654.74\)

3. Hydrodynamic force coefficients

  • Load formulation is Morison

  • Input code: Nondimensional coefficients

Quadratic drag coefficient with respect to d

\(C_{Qx}^ {fiber}\)

\(C_{Qy}^ {fiber}\)

Fiber rope

0.1

1.6

  • Added mass in tangential direction \(C_{Ax}=0.0\)

  • Added mass in normal direction \(C_{Ay}=1.0\)

  • Linear drag coefficient in tangential direction = \(C_{Lx}=0.0\)

  • Linear drag coefficient in normal direction = \(C_{Ly}=0.0\)

4. Linear stiffness model

Will create an axisymmetric cross section with constant axial stiffness.

Linear model has stiffness based on ABS upper-lower bound stiffness model based, i.e., for maximum offset (10) and line tension (30) calculation

5. Bi-linear model (Static-dynamic stiffness model)

Will create an axisymmetric cross section with Tension-elongation input for axial stiffness.

Relative elongation and axial force are selected based on ABS curve. The static and dynamic stiffnesses are 10 and 30 with mean tension of 40% MBL according to ABS

6. Syrope model

Using Fiber rope cross-section and Fiber Rope Model

  • AxisymmetricCrossSection.tmax: \(0.4*MBL\)

In Syrope model, static stiffness for new rope (i.e., original working curve stiffness) as well as aged rope (i.e., working curve stiffness) are chosen to be 8 and 14, respectively. The values are chosen based on quasi-static stiffness values for preliminary design in ABS. The stiffness for a new rope is assumed to be smaller than the post-installation rope address in ABS.

Simplified dynamic stiffness model based on mean tension: \(K_rd=A+BT_{mean}\) A and B coefficients are based on BV standard.

  • DynamicStiffnessCoefficientA [N]: \(18.5* MBL\)

  • DynamicStiffnessCoefficientB: \(0.33*100\)

7. Reference

  • ABS. Guidance Notes on the Application of Fiber Rope for Offshore Mooring. (2021).