In recent decades, the emphasis on renewable resources has grown considerably, leading to significant advances in the sector of wave energy. Nevertheless, the market cannot still be considered as commercialized, as there are still other obstacles in the mooring system for wave energy converters (WECs). The mooring system must be designed to not negatively impact the WEC’s efficiency and reduce the mooring loads. Firstly, the overview of the types of wave energy converters (WECs) are classified through operational principle, absorbing wave direction, location, and power take-off, respectively, and the power production analysis and design challenges of WECs are summarized. Then, the mooring materials, configurations, requirements, and the modeling approaches for WECs are introduced. Finally, the design of mooring systems, including the design considerations and standards, analysis models, software, current research focus, and challenges are discussed.

For semi-submersible platform applications in deepwater oilfield development in the South China Sea, selection analysis for mooring positioning system is one of the key issues in the design of offshore structures. Based on a semi-submersible platform model in three different water depths of 500 m, 1000 m and 1500 m, three types of mooring systems – catenary, semi-taut and taut – are considered, respectively. The three mooring systems have similar static restoring force characteristics and the same number of mooring lines and angle arrangement. The dynamic coupling effects between the semi-submersible platform and its mooring lines are investigated via numerical simulation. A three-dimension hydrodynamic finite element model of the semi-submersible platform is firstly built. The wave forces based on the diffraction theory are calculated using a boundary element method. The wind forces are obtained from wind tunnel tests using a 1:100 scale model of the platform, and the current forces are regarded as steady. The platform motion under the combined action of wind, wave and current is determined using the Runge–Kutta method under one-year and 100-year return period environmental conditions in the South China Sea. The specific numerical results, analyses and conclusions would be helpful in the selection of the mooring system and in the motion performance study of the semi-submersible platform preliminary design.

During the long-term service condition, the mooring line of the deep-water floating platform may fail due to various reasons, such as overloading caused by an accidental condition or performance deterioration. Therefore, the safety performance under the transient responses process should be evaluated in advance, during the design phase. A series of time-domain numerical simulations for evaluating the performance changes of a Floating Production Storage and Offloading (FPSO) with different broken modes of mooring lines was carried out. The broken conditions include the single mooring line or two mooring lines failure under ipsilateral, opposite, and adjacent sides. The resulting transient and following steady-state responses of the vessel and the mooring line tensions were analyzed, and the corresponding influence mechanism was investigated. The accidental failure of a single or two mooring lines changes the watch circle of the vessel and the tension redistribution of the remaining mooring lines. The results indicated that the failure of mooring lines mainly influences the responses of sway, surge, and yaw, and the change rule is closely related to the stiffness and symmetry of the mooring system. The simulation results could give a profound understanding of the transient-effects influence process of mooring line failure, and the suggestions are given to account for the transient effects in the design of the mooring system.