The continuous development of floating wind turbine technology is pushing platforms further offshore into deeper seas. Consequently, the water depth required for mooring is increasing, demanding higher standards for the mooring system. This study explores the mechanical properties, including wear resistance and quasi-static stiffness, of nylon, polyester, and high-strength polyethylene mooring ropes through experimental design, aiming to address the challenges faced by floating offshore wind turbines (FOWT) in mooring line safety. In conducting yarn-on-yarn abrasion tests, materials, twist, marine lubricants, and dry and wet environments were chosen as research variables to analyse and compare the wear and tear frequency of sample ropes. The study found that the degree of wear on ropes composed of different materials is affected differently by twist and dry and wet environments, and the application of marine lubricants can significantly extend the friction fracture cycle of yarns. To study the tensile properties and static stiffness characteristics of polyester and nylon ropes, the cables were divided into three stages: preloading, initial installation, and ageing. The strain and reversible elongation of the cables at each stage were analysed, and an empirical formula for quasi-static stiffness considering the creep coefficient of the ropes was established. The study found that the ropes had reversible elongation after being left stationary, the more thorough the running-in, the smaller the inherent deformation, and the more stable the structure. The static stiffness of the cables increased with the loading time and force; however, it eventually approached a constant value, and the stiffness of polyester cables was found to be greater than that of nylon ropes. These results provide a solid theoretical foundation and practical guidance for the material selection of FOWT cables, which contributes to advancing the application and development of FOWT in renewable energy.

Mooring ropes are essential components of ships and offshore floating structures and they are subjected to cyclic axial loads. This study investigates the evolution of the full-cycle stiffness of fibre polyester ropes under long-term static and dynamic loading. First, the static stiffness characteristics of the ropes, including the rope elongation properties at different stages, shrinkage rates, and creep coefficients after an idle period, are examined under static loads; an empirical formula for static stiffness is established. Second, the dynamic stiffness characteristics of the ropes are investigated under cyclic loads that are typical of platform production operations. The stabilities of the structure under different tensions are compared; the effects of mean tension, tension amplitude, and load cycle on the dynamic stiffness of the ropes are analysed and an empirical formula is established to predict the dynamic stiffness during the engineering design phase. The results of this study can be helpful for the rational design of deep-sea taut-leg mooring systems because they present the evolution of the full-cycle stiffness characteristics of mooring ropes.

Stress and strain analysis in lifted segments has been a prominent subject, especially with the increasing use of thin plates and higher pre-outfitting rates, which has brought to light the previously overlooked issue of torsional deformation. This research focused on investigating the mechanics of torsional deformation in thin-plate open-section segments with nonuniform weight distributions during lifting. By simulating the effect of the pre-outfitting weight using offset weights, establishing reasonable lifting point constraints, and creating a typical segment lifting analysis model, the results obtained through nonlinear and linear finite element analyses were compared. Extensive data was employed to establish the relationship between the torsional deformation and offset weights, using the principle of energy and the linear regression method. This analysis uncovered substantial disparities between the linear and nonlinear methods, with the linear approach failing to provide accurate stress and strain for torsion. Furthermore, the stress distribution obtained from nonlinear finite element analysis adhered to contemporary torsional theory. This paper underscores the nonlinear nature of torsional deformation, elucidates the influence of the weight distribution, and establishes a functional relation between the torsional deformation and offset weights, offering a robust tool for optimizing outfitting design and construction schemes.