Wave load characteristics on a hybrid wind-wave energy system

Following the development of offshore wind turbine (OWT) systems and wave energy converters (WECs), there is an increasing demand for the development of hybrid systems that combine OWTs with WECs, for the purpose of reducing the Levelized Cost of Electricity (LCOE) of WECs by sharing foundations, increasing overall power output, and optimizing the utilization of marine space. One of the hybrid systems integrates WECs with the most widely adopted foundation used by existing wind farms, i.e. the fixed monopile foundation. While existing research mainly focuses on the characteristics of loads and power performance of WECs, the corresponding characteristics related to wave load on the monopile foundation and the hybrid system play a critical role in securing the safety and stability of the monopile foundation but is limited in the available literature. This paper presents an analysis of wave load characteristics on a fixed monopile foundation of a 15 MW OWT integrated with a torus-shaped heaving WEC using the ANASYS-Aqwa adopting the linear potential theory. The structure is subjected to regular and irregular waves in the operational sea conditions. The power take-off (PTO) system of the WEC is modelled by applying a linear damping in the present numerical work. The results suggest that the PTO damping has an insignificant impact on the wave load statistics. It is further confirmed that, the integrated WEC effectively reduces the wave load and overturning moment acting on the monopile foundation within a wide range of wave conditions. Moreover, the presence of the monopile also reduces the horizontal wave load on the WEC. However, the overall load on the hybrid system, which is the resultant force of horizontal wave force acting on buoy and monopile, is higher than that experienced by the monopile foundation of the OWT prototype. To the best of our knowledge, this is the first work investigating into the effect of integrated torus-shaped WECs on wave loads affecting fixed foundations. The findings offer valuable insights for the design and deployment of such hybrid systems in the near future.