Evidence points to increasing the development of floating wind turbines to unlock the full potential of worldwide wind-energy generation. Barge-type floating wind turbines are of interest because of their shallow draft, structural simplicity, and moonpool-damping effect. Based on the BEM potential flow method, this study uses ANSYS-AQWA software to create a floating-barge moonpool platform model equipped with an OC5 NREL 5 MW wind turbine, to study the effect of the damping lid method on the resonance of the moonpool gap water, the wind–wave coupling effect, and the dynamic response of the FOWT and mooring system after single-line and double-line failure. The results show that the damping lid method, based on the potential flow theory, can effectively correct the effect caused by the lack of viscosity; the effect of a single breakage of upwind mooring lines on the motion is mainly in the sway and yaw modes, and after mooring line 8 breaks, the maximum tension of the adjacent mooring line increases by 2.91 times compared to the intact condition, which is 58.9% of the minimum breaking strength; and the breakage of two mooring lines located at one corner leads to a surge drift of up to 436.7 m and a cascading failure phenomenon.

Monopiles are commonly utilized in offshore wind farms but are prone to non-linear wave loads and run-ups, significantly affecting their engineering design. Therefore, it is crucial to pursue a complete understanding of the non-linear wave action on monopile foundations. Both numerical and experimental investigations on the non-linear wave loads and run-ups on an offshore wind turbine monopile foundation are performed in this paper. The experiment is carried out at a scale of 1/30 in a wave flume at the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, in which the wave loads and run-ups along the monopile are measured. Based on the second-order potential flow model and time-domain higher-order boundary element method (HOBEM), the related numerical tests are conducted to study the non-linear effects further. It is found that the present non-linear potential theory is sufficient for the simulation of wave force and run-ups on the monopile in the range of wave slope kA < 0.15 before wave breaking. “W” type distribution of wave run-up along the monopile is found, in which the peak value occurs at the frontward side (i.e., θ =180°) and is the maximum due to full reflection; the two symmetrical minimum amplitudes lie in the zones of (45° ≤ θ ≤ 90°) and (270° ≤ θ ≤ 315°), whose positions shift downward with the increase of wave non-linearity. Energy transfer among the fundamental wave component and higher-order components is also found, which is most apparent on the backward side. Besides, the transverse resonance occurs in the wave flume due to the wavelength being near the flume width, which induces the wave run-up at the backward position larger than that at the frontward position.

Offshore wind turbines serve as critical infrastructure components in marine renewable energy systems, enabling sustainable energy extraction within offshore engineering frameworks. Monopile foundations for offshore wind turbines in deep-water environments are subjected to strong nonlinear wave actions. This study introduces a novel composite monopile foundation specifically designed for deep-sea applications, with its fully nonlinear hydrodynamic performance systematically investigated using potential flow theory. The novel hybrid monopile incorporates a concrete-filled double-skin steel tubular (CFDST) configuration to reduce pile diameter at water level. In the numerical model, the higher-order boundary element method (HOBEM) is implemented to resolve boundary value problems at each temporal iteration. Following numerical validation, nonlinear wave loading and run-up characteristics for the CFDST hybrid structure are quantified, while the limitations of Morison’s equation for large-scale structures under strongly nonlinear wave conditions are concurrently assessed. Results indicate that CFDST implementation effectively attenuates both nonlinear hydrodynamic forces and wave run-up amplitudes, enabling safer and more economical design approaches for deep-water offshore wind turbine foundations.