Applicability of a Simplified Model of a 15MW Wind Turbine for a Mooring Fatigue Study

Mooring system of floating wind turbine design, as conditioned by fatigue analysis, requires time-consuming simulations. But to provide relevant solutions for the multiple coming tenders, efficient methodologies need to be developed to design quickly optimal floating platform mooring for specific metocean data and project constraints. This paper presents a comparison between a mooring fatigue assessment calculated with two standard detailed modelling of a 15MW wind turbine and a simplified Drag and Lift Model (DLM) based on global coefficients at hub often used in floating offshore wind preliminary analysis to carry out extreme analysis. The present contribution is here focused on the proper assessment of a quantitative error introduced by the simplified turbine model in the mooring fatigue assessment, and the evaluation of the missing contributions such as 3P excitation or low frequency induced by turbine control. Two different control approaches are assessed here to capture a range of coupled behaviour which have been observed on project. It has been shown that the DLM approach is accurate to carry out analysis under extreme conditions, but also gives relevant fatigue results for the most fatiguing lines. In general, the order of magnitude is consistent even for low damage. All the calculations have been made using DeepLines Wind TM software.