Comparison study on mooring line models for hydrodynamic performances of floating offshore wind turbines

The mooring system plays a crucial role in the seakeeping ability of floating offshore wind turbines (FOWTs) but complicates the overall dynamics of the system. Many quasi-static (QS) and dynamic models for mooring analysis exist but a comprehensive comparison among open-source or semi open-source codes in various scenarios is rare. In the present study, six mooring models including three dynamic and three QS ones are assessed. The three dynamic models are the local discontinuous Galerkin (LDG) finite element method (FEM), the lumped mass (LM) method and the finite different method (FDM), and the three QS models are the piecewise extrapolation method (PEM), the catenary and the QS of MAP. Three groups of tests involving catenary line under fairlead excitation, hanging line with axial excitation and FOWT in waves are conducted. The first two test groups focus on single line dynamics to assess among the three dynamic models while the third test group focuses on coupled hydro-mooring modeling with the FEM, PEM, catenary and QS coupled to OpenFOAM. The test results show that there are substantial differences among the models in various scenarios. And the LDG FEM and LM models are recommended to be applied in realistic FOWT hydrodynamics problems.