Wave Motion Characteristics of a Low-Rigidity FOWT with a Guy-Wire Supported Tower and Single-Point Mooring Configuration

The study aims to understand the wave motion characteristics of the Optiflow concept, a low-rigidity FOWT with a guy-wire supported tower, through wave tank experiments and numerical calculations using UTWind code. Three main effects were investigated: wave height, wave direction, and mooring line configuration. The Optiflow presented nonlinear motion behavior in waves as wave height effects due to the different levels of viscous damping. The single-point mooring system played a significant role; thus, a coupling of vertical motions (heave, pitch, and sometimes roll) was observed. In addition, it showed a different behavior due to the wave incidence angle. First-order motions were affected by the mooring line configurations as not expected from oil and gas knowledge; thus, the effect of the mooring line can be pronounced for very-light FOWT as the Optiflow. Additionally, the cancelation point (or waveless) response was observed as typical behavior of semi-submersible type floaters in all the experiments. The comparison of the results from the experiment and numerical UTWind code simulations confirmed that the agreement was satisfactory except for the resonance period since the viscous effect had a significant impact on motions, which was not accurately considered in the numerical code.