Study on Evaluation of Motion and Elastic Response of a New Type of FOWTs in Waves Using Multibody Dynamics Analysis

Floating offshore wind turbines (FOWTs) have been attracting a lot of attention as a main energy source for a carbon-neutral society. Although it is said that the costs of commercialization of FOWTs are still high, many studies have been conducted to rationalize costs. The main cost is construction of the floating structure, and now many novel FOWTs concepts have been proposed to reduce it. The unique shape and structure of one of those FOWTs, which consist of a steel tower and concrete lower hulls with wires holding them rigid, make it difficult to evaluate their safety using existing numerical analysis methods. In this study, we investigated a multi body dynamics analysis method for the novel floater. The analysis method was employed to reproduce the behavior in regular waves, considering the elastic response of the floating body. A model test was also carried out to verify the accuracy of the analysis method. In the model test, a special large-size scale model was used, which was manufactured in the same way as the actual model. Comparison of both results, i.e., the analysis and the model test, showed good agreement in floater motions, mooring tensions, and wire tensions. On the other hand, differences were also observed between them for some wave period conditions. It is possible that the asymmetry of the floating structure and its columns that penetrate the water surface at an angle caused the differences in the estimation of the fluid force acting on the columns. Through the analysis, the effectiveness of the FOWTs concept on reduction its tower base load was also confirmed.