Mooring System Failure Detection Methods for Floating Offshore Wind Turbines Using Motion Measurement: Part 1 Tank Tests for Catenary Mooring Systems

Abstract The goal of this study is to develop a method for assessing the integrity of the mooring systems in floating offshore wind turbines (FOWTs) by measuring floater motions. As an initial investigation, we examine a method to detect mooring line failures based on the floater motions. This approach uses environmental data, such as wind speed and direction, to define an expected range of floater positions, which is then directly compared to the floater’s current position to detect any potential failures in the mooring system. In this paper, we conducted a tank test to investigate the relationship between the floater position and the failure of the mooring line system. A 1/100 scale FOWT model consisting of a 15MW wind turbine and semi-submersible with catenary mooring systems was utilized in the experiment. Both all-chain mooring and hybrid mooring consisting of chain and fiber rope were used to clarify the impact of differences in mooring configurations. In the experiment, two failure conditions, one involving a line breakage and the other involving anchor shifting, were investigated to compare with the results in an intact mooring condition. The experiment under steady wind-only loads revealed that the FOWT equilibrium position clearly changed as a result of mooring line failure. When both steady wind loads and wave loads were applied, the time-averaged floater position converged to the position observed in the case with steady wind-only loads. These findings demonstrate that our proposed method is applicable for detecting potential failures in the mooring systems.