Response Characteristics of the DeepCwind Floating Wind Turbine Moored by a Single-Point Mooring System

Abstract

In recent years, the SPM (Single-Point Mooring) concept has been widely employed in several branches of the naval architecture and marine engineering field, such as FPSOs (Floating Production, Storage and Offloading units), offshore oil rigs, etc., but not yet popular in the offshore wind energy. To investigate the response characteristics of an SPM-moored FWT (Floating Wind Turbine), in the present work, we perform a numerical study on the DeepCwind semisubmersible wind turbine, using the state-of-the-art open-source tool FAST. The free-decay test results show that the SPM layout affects the natural periods of the wind turbine in rotational modes, as well as the mooring stiffness of the diagonal rotational and crossing rotational-translational terms, especially in relation to the yaw mode. Comparisons of the RAOs (Response Amplitude Operators) elucidate that the presence of wind influences significantly the sway, roll and yaw motions of the SPM layout. Finally, the weathervane test shows that an asymmetry exists in the free-yaw motion response when the semisubmersible wind turbine is moored by an SPM system.

Proposal of a Novel Semi-Submersible Floating Wind Turbine Platform Composed of Inclined Columns and Multi-Segmented Mooring Lines

“…Although there is no wind and the water is still, the radiated waves produced by the initial motion of the platform will still generate hydrodynamic loads on the platform and the mooring system. The details of the settings of the verification case can be found in the study of Liu et al [62]. The motions in surge, heave and pitch directions in the time domain obtained by FAST and those by AFWT are shown in Figure 6, where satisfactory agreement is achieved.…”

Enhanced Endo's approach for evaluating free-surface Green's function with application to wave-structure interactions

“…Table 1. Geometrical specifications of the DeepCwind semisubmersible platform (Robertson et al, 2014;Liu et al, 2018b). Hydrodynamic mesh is generated only for the immersed part of the platform, and the waterplane at the cross-sections of the columns intersecting the mean sea surface.…”

Numerical Study of a Proposed Semi-Submersible Floating Platform with Different Numbers of Offset Columns Based on the DeepCwind Prototype for Improving the Wave-Resistance Ability

“…where, x F and z F are the cable profile in horizontal and vertical planes at distance s along the line, respectively; F H and F V are the horizontal and vertical components of the effective tension in the mooring line at the fairlead [38]; EA is the cross-section axial stiffness; L denotes the upstretched line length; C B is the coefficient of static friction between the seabed and the mooring line; ω = gA(ρ c − ρ) is the weight per unit length in the submerged fluid; ρ c is the cable density, ρ means the fluid density; and g is the acceleration due to gravity. It is worth noting that Equations (1) and (2) are established in the local coordinate system and can be solved by an iterative method.…”