Out-of-plane bending stiffness and hotspot stress based on advanced numerical analysis techniques

Abstract

ABSTRACTThis paper aims to presents an integrated procedure to reach the out-of-plane bending (OPB) moment-induced hotspot stress distribution for the mooring chains of an 8MW class floating offshore wind turbine platform (FOWT). Three-link models of the mooring chains were used to obtain the OPB stiffness, mid-span stress distribution, hotspot stress, and stress concentration factor based on the prescribed rotation approach (PRA), direct tension approach (DTA), and empirical formula. Multi-link analyses were also conducted to build a tension angle-interlink angle relationship between two successive links at a given tension level. A combination of three-link and multi-link analyses produced the relation of the hotspot stress-tension angle. After a stress interpolation procedure for the hotspot stress history, the hotspot stress range distributions were presented using rainflow counting technique. The tension-induced stress range distribution well followed the Rayleigh distribution, while the OPB moment elevated the hotspot stress which will seriously affect the fatigue accumulation.