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This paper presents three different wind-wave hybrid systems (HSs) with multiple point-absorption wave energy converters (WECs) integrated onto a floating semi-submersible wind turbine (WT). The focus of the present study is to explore the effects of the second-order wave forces on the dynamic behavior of the platform in the HS, including the platform motion and the mooring line tension, under both operational and extreme sea states. ANSYS/AQWA based on 3D diffraction/radiation potential theory is used to conduct numerical investigation on the second-order hydrodynamics of the HS. To ensure the reliability of the investigation, the validations of the semi-submersible platform and point-absorption WEC are done based on the available experimental data. Additionally, two models, "1st-order" and "1st&2nd-order", are set up for comparative analysis, to highlight the significance of the second-order forces. The simulation results show that the second-order hydrodynamics have a significant influence on the surge and pitch responses of the platform, but almost no effects on the heave response. In addition to this, ignoring the second-order hydrodynamics will significantly underestimate the mooring line tension response. Overall, this study suggests that the second-order hydrodynamics should be considered in the design of wind-wave HSs, in order to ensure their performance and safety, especially under the severe sea states.
Zhang et al. (Mon,) studied this question.