Reference paper for subroutine catenary

Wind & Water Structural Analysis
1

Dear all,

I am diving in the source code of Moordyn. And when initializing the mooring line shape, Moordyn will call subroutine ‘catenary’ to use the analytical solution to calculate the initial shape.

But I am not familiar with the adopted formulas. Would anyone suggest some relevant papers which derived the analytical solution for mooring line?

Below is the description for subroutine catenary:

      SUBROUTINE Catenary ( XF_In, ZF_In, L_In  , EA_In, &
                            W_In , CB_In, Tol_In, N    , &
                            s_In , X_In , Z_In , ErrStat, ErrMsg    )

         ! This subroutine is copied from FAST v7 with minor modifications

         ! This routine solves the analytical, static equilibrium equations
         ! for a catenary (or taut) mooring line with seabed interaction.
         ! Stretching of the line is accounted for, but bending stiffness
         ! is not.  Given the mooring line properties and the fairlead
         ! position relative to the anchor, this routine finds the line
         ! configuration and tensions.  Since the analytical solution
         ! involves two nonlinear equations (XF and  ZF) in two unknowns
         ! (HF and VF), a Newton-Raphson iteration scheme is implemented in
         ! order to solve for the solution.  The values of HF and VF that
         ! are passed into this routine are used as the initial guess in
         ! the iteration.  The Newton-Raphson iteration is only accurate in
         ! double precision, so all of the input/output arguments are
         ! converteds to/from double precision from/to default precision.

Regards,
Ran

2

Dear @Ran.Tu,

See the section titled, “Mooring System Modelling” in my 2009 Wind Energy journal publication: https://onlinelibrary.wiley.com/doi/10.1002/we.347. Please note, however, that there was a copy-paste error in Eq. (20b), which should be:

zF(HF,VF) = HF/w*[ SQRT( 1 + (VF/HF)^2 ) - 1 ] + VF^2/(2EAw)

Best regards,

3

Thank you, Dr. Jason. I will study this paper.

Regards,
Ran