Applicability analysis of catenary anchor leg mooring system subjected to bending effects in Weizhou sea area of South China Sea

This study focuses on the applicability of the catenary anchor leg mooring (CALM) system subjected to bending effects in the Weizhou sea area of the South China Sea. The survivability of the mooring system under extreme environmental conditions in the Weizhou sea area of the South China Sea was analyzed, and a verification method for ultimate mooring force considering the bending effects was proposed. The joint probability distribution model of significant wave height and mean zero up-crossing period in the Weizhou sea area of the South China Sea was established. Based on this model, the 100-year return period contour of significant wave height and mean zero up-crossing period was calculated and plotted. Combined with the 100-year return period wind condition and the 10-year return period flow condition, the ultimate verification sea state of the Weizhou sea area of the South China Sea was constructed. A time-domain hydrodynamic analysis of the CALM system was conducted based on the Morison Equation, and the most probable maximum mooring tensions of R4S studless mooring chains with diameters of 76.2, 88.9, and 101.6 mm were evaluated using the Gumbel Distribution. Finite element analysis was performed to examine the effects of in-plane and out-of-plane bending of mooring chains caused by the chain stopper and hawse pipe arrangement, and the resulting stress distribution in the mooring chain was analyzed. Finally, the applicability of the CALM system in the offshore Weizhou area of the South China Sea was evaluated. The analysis results showed that when using the mooring arrangement with the chain stopper and hawse pipe, the mooring chains experienced additional stress concentration due to in-plane and out-of-plane bending, requiring a bending safety factor of 1.3. The mooring system with 101.6 mm diameter chains was suitable for deployment in the Weizhou sea area of the South China Sea. The system with 88.9 mm diameter chains met the standard verification requirements but did not satisfy mooring analysis criteria when considering the bending effects between chain links. The system with 76.2 mm diameter chains did not meet the standard verification requirements.