Numerical calibration of the mooring system for a semi-submersible floating wind turbine model

Abstract

Numerical modelling of the floating offshore wind turbine (FOWT) dynamics plays a critical role at the design stage of a floating wind project. Still, there exist challenges for verification of efficient engineering models against experimental results. Recently, an experimental campaign was carried out for a 1:96 downscaled model of the OC4-DeepCWind semi-submersible platform with mooring lines made of fibre ropes and chains. Leveraging the results of this campaign, this paper focuses on development and calibration of a numerical model for the semi-submersible platform with a focus on the dynamic responses under bichromatic waves. In the numerical model, the hydrodynamic loads are modelled based on the potential flow theory with Morison drag. The lumped mass method is applied to model the mooring system. Both free decay tests and bichromatic wave conditions are considered in the model calibration process, and key uncertain parameters (e.g., mooring line length) that affect the response have been identified and discussed. Using the proposed calibration procedure, we establish a reasonably good numerical model for prediction of the platform motion and mooring dynamics. The low-frequency responses of the platform under bichromatic waves are well-captured. These outcomes contribute to the development of efficient numerical FOWT models under experimental uncertainty.