Multi-scale approach for chain-mooring OPB-induced failure considering time-varying interlink bending stiffness and fairlead condition

In this study, a mull-scale approach concept is introduced to estimate OPB (out of plane bending)-induced failure considering time-varying interlink bending stiffness by using both high-fidelity nonlinear-FEM (finite element method)-based local structural analysis and low-fidelity global-system-simulation program so that they can mutually be interfaced during the time-stepping procedure. In addition, time-varying interlink-angle measurement and its use with respect to the global-system simulation are devised. For the fully-coupled hullmooring-riser global dynamics simulation, in-house program CHARM3D is extended to accommodate the timevarying OPB interlink stiffness. The hot spots for OPB fatigue are selected from the high-fidelity local FE analysis including residual stress after proof-loading test. It is clearly shown that interlink angles are under-estimated if chain-hawse is not modeled in the global simulation. The OPB interlink angles, bending moments, and accumulated fatigue damages greatly increase when the fairlead connection is changed from hinged to fixed condition. Moreover, fatigue damage is underestimated if the residual stress effect is not considered.