Numerical Analysis of Mooring-Induced Trenches in Floating Offshore Wind Turbines

Abstract

Abstract. Floating offshore wind turbines (FOWTs) are significantly influenced by their mooring systems, where the complex interaction between anchors, mooring chains, and seabed soil can lead to trench formation. This trenching phenomenon can adversely affect the overall performance and operational safety of FOWTs. In this study, a coupled numerical modeling approach is developed to systematically investigate the evolution of seabed trenches induced by mooring chains, considering both the dragging and embedded sections. An innovative multibody dynamic model of the anchor chain–seabed system is established, characterizing the trench formation process through motion equations for three stages: the underwater, dragging, and embedded sections. A detailed anchor chain–soil interaction model is also constructed using abaqus. Full-scale simulations validate the proposed method with a calculation error below 6.4%. A life-cycle case study of a 5-MW catenary-moored FOWT shows that the maximum trench depth can reach 3.1425 m over 20 years. Additionally, the influence of trench formation on fatigue limit state (FLS), ultimate limit state (ULS), and accidental limit state (ALS) limit state evaluations—specifically mooring line tension and platform motions—is quantified. The proposed coupled analysis method offers a practical tool for mooring system design and presents potential for improving both reliability and cost-effectiveness in FOWT projects.