The experimental and numerical investigations of the hydrodynamic characters have been carried out in the present study for the semi-submersible floating offshore wind turbine, wind and current have not been considered in this phase of the research. It was found that the viscous damping levels vary with sea states and the results obtained with experiments and simulations are compared, focusing on the heave, roll and pitch response spectrum and short-term statistics, it is shown that the frequency spectrum analysis method may underestimates the response and ignores the pitch-surge coupling or roll-sway coupling. These results show that the designer should be fully aware of the limitations of frequency spectrum analysis in shallow water and consider the potential impact during its design in the early scheme comparison.
Offshore wind turbines (OWTs) have become an attractive solution to harvest electric power from a renewable source in China and has seen a rapid development in recent years. Different from Europe and American, the continental shelf of China has a wide extension area and a slow slope, the developed offshore wind farms in China are located in shallow water (< 50m). In shallow water, bottom-fixed foundations are usually used to support OWTs, such as monopiles, gravity-based structures, jackets and buckets (Bo Liu et al.2020). However, Floating Offshore Wind Turbine (FOWT) may be an alternative worth considering from an economic perspective in shallow water, such as application of large capacity wind turbines and specific construction conditions.
FOWTs are mainly divided into four categories: semi-submersible (Semi), spar, barge and tension leg platform (TLP). Within the four main FOWT concepts, the Semi-FOWT is receiving significant attention due to several advantages, namely: these types of platforms can be fully assembled onshore and towed ready-to-use to their final destinations; the available mooring systems are well-known and cost competitive; if properly designed, downtime in operational sea states, due to excessive platform motion, is low (Simos A N et al.2018).
