## 5 Conclusions  
The current study investigates the interaction effect of waves and currents on the dynamic response of a CSS FOWT. For simulating such interactions, a coupled model of the CSS FOWT including a floating platform, catenary mooring cables, and the fluid-structure interaction between these components was established, and the interaction model for irregular waves and uniform currents was applied for this study. The interaction impact of waves and currents on the dynamic responses of the CSS FOWT was investigated. The NREL 5-MW wind turbine installed on top of the CSS was used in the numerical simulations. The CSS FOWT responses to irregular waves only, irregular waves and currents without interaction, and irregular waves and currents with interaction were analyzed, resulting in the following conclusions:  
1. The interaction between waves and currents significantly impacts the dynamic motion responses of the CSS FOWT, especially when waves travel on opposite currents. Figure 19: PSD of the tower base forces for case 8 in the Y direction. When the coupled interaction between currents and waves is taken into account, the resulting variation in dynamic motion responses is observed to be 24.3% higher as compared to cases where this interaction is not considered. The interaction influence is predicted to be more significant for large currents and when wave profiles change considerably from those suggested by linear wave theory. 2. The wave-current coupling interaction plays a crucial role in influencing the dynamic responses of the mooring tension of the CSS FOWT, particularly in scenarios where waves propagate against opposite currents. When the coupling interaction between currents and waves is considered, the observed variation in dynamic responses of mooring tension is found to be 22.7% greater than in scenarios where this interaction is disregarded. It is anticipated that the influence of this interaction will be more pronounced in the presence of strong currents and when wave profiles deviate significantly from those predicted by linear wave theory. 3. The interaction effect of waves and currents has a significant impact on the dynamic responses of the CSS FOWT, particularly when fluid-structure interactions are considered. In the analysis of CSS FONTs, it is crucial to consider the effect of wave-current interaction. The method of simple superimposition of the effects of the waves and the currents overestimates the dynamic response for the case of the forward moving current (i.e., the current moving in the same direction as the waves) when compared with the estimates from the full interaction. On the contrary, this simple superposition of the effects of the waves and the currents underestimates the dynamic response of CSS FONTs when the current is moving in the opposite direction of the wave propagation with respect to the results obtained with full interaction. 4. The wave-current coupling interaction has limited influence on the tower base shear forces and bending moments. To summarize, it is shown that the coupled interaction effect of waves and currents is essential in the consideration of the dynamic analysis of CSS FONTs, especially for the situations where the semi-submerged FONTs are located in areas of currents opposing the propagation of surface waves. B.W. : Conceptualization, investigation, methodology, software, writing--original draft, writing--review and editing. B.B. : Conceptualization, supervision, methodology, writing--review and editing. L.C. : Conceptualization, methodology, writing--review and editing. N.H.: Conceptualization, supervision, funding acquisition, writing--review and editing. W.W.: Conceptualization, supervision, funding acquisition, methodology, writing--review and editing. All authors have read and agreed to the published version of the manuscript. The first author gratefully acknowledges the financial support from the Chinese Scholarship Council under the State Scholarship Fund. The support of the State's Key Project of Research and Development Plan (No.