Development of a numerical mooring line model for a floating wind turbine based on the vector form intrinsic finite element method

Abstract

The utilization of renewable energy has great significance to reduce CO2 emissions. Floating offshore wind turbines (FOWTs) is regarded as most cost-effective solution to harness the offshore renewable energy in deep-water. Fully coupled analysis is regarded as the state-of-art simulation method for FOWT's design and analysis. Until now, various methods (lumped mass model, quasi-static model, finite element model et al.) are used in mooring line modelling in the fully coupled simulation for FOWTs. In this paper, a new dynamic model for catenary mooring line is proposed based on the vector form intrinsic finite element (VFIFE) method. This method is designed to calculate motions of a system, which the motion may include large rigid body motions and large geometrical changes, or very large deformations. The inertia and hydrodynamic and the seabed interaction are contained in this model. Newton's law of particle is assumed to derive the governing equations of motion. An explicit algorithm is used to calculate the numerical results. The feasible and accurate of the dynamic model are verified by comparing with the experimental data and other validated codes. In the comparisons the results of VFIFE method has a good agreement with the references. Thus, the dynamic model proposed in this paper is capable for the dynamic analysis of mooring lines. Furthermore, the influence of the forced motion frequency (and amplitude) of mooring system on the hysteresis loop area is studied, which reveals the mechanism of the energy dissipation from the viscous damping of fluid and the gravitational potential energy of the line.