The global performance of the Korea research institute of ships and ocean engineering (KRISO) square-type semi-submersible multi-unit floating offshore wind turbine (MUFOWT) in irregular waves is numerically simulated by using the multi-turbine-floater-mooring coupled dynamic analysis program. The developed time-domain numerical-simulation tool is extended from the FAST/CHARM3D coupled dynamics program for the single turbine on single floater. FAST has been developed by the National Renewable Energy Laboratory (NREL) for years for the single unit. Recently, KRISO has designed and studied the square-type MUFOWT, in which four 3MW wind turbines are installed at each corner of a single floater. Additionally, twenty four point-absorber-type linear-generator-based wave energy converters are set up - six wave energy converters at each side of the platform. For verification, KRISO performed a series of model tests for this MUFOWT with 1:50 Froude scale. In this paper, the MUFOWT simulation program is used to reproduce the KRISO model test results. In the fully coupled multi-turbine/hull/mooring dynamic simulations, the complete second-order difference-frequency wave forces are also included. The analysis results are systematically compared with the model test results, which shows reasonable correlation between them.
The importance of clean renewable energy has been underscored to secure new energy sources and protect environments. Especially, wind energy is appealing since it is economically competitive, technologically proven, infinitely renewable, and does not make any waste or carbon emission. Although they are considered to be more difficult to design than fixed offshore wind turbines, floating wind turbines have many advantages compared to onshore or bottom fixed offshore wind turbines. In general, they are less restricted by governmental regulation and residents' opposition, with higher-quality wind, and less sensitive to space/size/noise/visual/foundation restrictions. In this regard, if the technology is completely developed, floating offshore wind turbines are expected to be more popular to generate considerable amounts of clean renewable energy at competitive prices compared to other energy sources (Henderson et al., 2002; Henderson et al., 2004; Musial et al., 2004; Tong, 1998; Wayman et al., 2006).
