Energy consumption is increasing rapidly with population growth and technological development. In particular, the excessive development and use of fossil energy cause a global pollution problem, and excessive greenhouse gas emissions, including carbon dioxide, leads to global warming and various environmental problems. Therefore, it is essential to develop technologies for renewable energy, which is a sustainable and eco-friendly energy source (Muliawan et al., 2013;Ullah et al., 2020).Among renewable energy sources, offshore wind energy, wave energy, and current energy, which are representative offshore energy sources, require future-oriented and continuous technology development. In particular, many technologies have been developed for offshore wind energy because it has benefits in terms of wind homogeneity and speed as well as the installation location compared to onshore wind energy (land-based wind energy). Large-scale commercial power generation is also possible because it is free of the restrictions of many wind turbine installation spaces and noise (Bae and Kim, 2013). As offshore wind turbine technology has grown into a major energy source worldwide, including in Europe, many studies have been conducted to increase the economic feasibility of offshore wind turbine platforms (Global Wind Energy Council Global, 2019).A combined wind-wave energy platform in which wave energy converters (WECs) are attached to floating wind turbines has been reported as one way to increase the economic feasibility of floating offshore wind turbine (FOWT) in many studies. The combined energy platform is based on the typical characteristics of ocean environments: relatively high waves accompany high wind speeds. Moreover, using two energy sources makes it possible to reduce the energy extraction variability of a single offshore wind turbine and increase the economic effects (Kim et al., 2015). As a combined wind-wave energy platform type, there is a combined platform model that combines the OC4 model (Robertson et al., 2014), a semi-submersible wind turbine structure disclosed by the National Renewable Energy Lab (NREL) in the United States, with Wavestar-type WECs (Hansen et al., 2013). Si et al. (2021