This paper summarizes our recent collaborative/competitive works on floating offshore wind turbines (FOWTs) among four universities including Osaka Prefecture Univ., Osaka Univ., Yokohama National Univ., and Nihon Univ. The tasks assigned to each member were to develop the respective FOWT designs which could support 5MW class wind turbine, then to fabricate a scale model based on their own concept, and finally to evaluate the performance by tank tests under prescribed environmental (wind and wave) conditions. Osaka Prefecture Univ. adopted TLP concept, Yokohama National Univ. semi-submersible concept, Nihon University SPAR concept while Osaka Univ. also adopted semi-submersible, however, with single-point mooring. All the measured data were collected and compared among the four designs. It turned out that: (1) All the proposed deigns suffice criteria in terms of motion performance which were assumed at the beginning of the study. (2) The TLP type shows the most favorable performance among the four while the SPAR type shows largest acceleration in almost all the range of environmental conditions. The large acceleration may pose a problem of maintainability. (3) The SPAR type suffers the gyration effects more than the other types. (4) The RAOs of motions under combined wind and wave loads are almost the same as those under only wave loads for all the concepts but the single-point moored semisubmersible. (5) The difference of the RAOs for the single-point moored semisubmersible may be ascribed to the larger coupling effects between the main floater and the mooring system under the combined loads.

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