A Finite Element Analysis Investigation of Fatigue and Corrosion of Floating Offshore Wind Turbine Mooring Lines

Abstract

With the rising demand for renewable energy, floating offshore wind turbines have gained importance, particularly in regions where deep waters prevent the use of traditional monopile structures. These floating turbines rely on mooring lines for stability against environmental conditions, particularly when facing strong winds and high waves. Ensuring a satisfactory lifetime and health of mooring lines is critical. Moreover, degradation can compromise the turbine’s functionality or even lead to catastrophic failures. While direct monitoring is ideal, it is often hampered by high costs and extensive maintenance. This Master’s thesis introduces a novel method to assess mooring line degradation. The proposed approach simulates the impact of environmental conditions on the mooring lines, considering various forces and weather scenarios. The research presents modeling of fatigue and corrosion effects along the mooring line. A unique corrosion model calculates variations based on seawater’s oxygen and temperature profiles. Concurrently, mooring line stresses are deduced from real-world environmental conditions. Integrating these, a finite element model is constructed to analyze different load scenarios and the onset of corrosion on line degradation. The model considers the joint impact of corrosion and fatigue on mooring lines, including the influence of hydro static pressure and out-of-plane bending. Validation of this methodology draws upon existing research and experimental results on mooring lines.