Out-of-Plane Bending Moment-Induced Hotspot Stress Evaluation Using Advanced Numerical Technique

There have been various studies to predict out-of-plane bending (OPB) moment-induced stresses in mooring chain links. Recently, the BV guideline as one of the deliverables from OPB JIP reported empirical formulas to predict the nominal OPB moment-induced stress with suitable concentration factors (SCFs) so that prediction of the OPB moment-induced hotspot stresses can be available. A non-linear finite element analysis technique has been developed to more accurately estimate the OPB moment-induced hotspot stress. There has been no choice but to apply prescribed rotation to generate the OPB moment in this numerical technique (existing approach). Pointing out some disadvantages in the BV guideline and existing approach, an advanced numerical was proposed to simulate more realistic tension-induced OPB mechanism. In the present paper, basic differences were presented in terms of numerical simulation techniques, nominal OPB moments, and hotspot OPB stresses. In order to show differences of the stress distributions and the hotspot OPB stresses between existing and advanced approaches, a benchmark chain link model was constructed in which the nominal diameter was 107mm. From the comparison of stress distributions in straight parts of the link, significant differences were found between the existing and advanced approaches. The existing approach more developed the compressive stresses due to the prescribed rotation-induced OPB moment than the advanced approach. This also led to more increased hotspot OPB moments.