Design and hydrodynamic analysis of a new web-type mooring system

”Y”-type branching is a common load-bearing topology in natural networks such as spider webs, where pretensioned radial and circumferential threads provide multiple load-transfer paths and enhance resistance to local damage. Inspired by this mechanism, this study proposes a taut web-type mooring layout for offshore floating platforms, with the main objective of redistributing mooring loads rather than significantly reducing platform motions. This concept is applied to the OC6 semi-submersible platform and compared with a conventional three-line mooring layout. The time-domain simulations are performed in OrcaFlex with consideration of the second-order wave loads. A fair comparison is established by matching the fairlead geometry, draft after installation, mooring static pretension and immersion angle. Results show that surge, heave, pitch and yaw responses remain broadly comparable to those of the conventional layout. Considering all incident wave headings under the representative regular-wave condition, the polar-area metric calculated from the three main-line tension RAOs is reduced by approximately 48% on average. The full-frequency assessment further shows that the polar-area reduction remains above 20% at all considered frequencies and reaches approximately 50% at its maximum. The reduced main-line response reflects the combined influence of the modified restoring characteristics and the additional load-transfer paths introduced by the branched topology. The branching angle shows limited influence within the admissible range, while the apparent optimum outside this range is interpreted only as an extrapolation trend. Irregular wave and single sub-line failure cases further demonstrate improved main-line tension balance and direction-dependent post-failure load redistribution, while comprehensive fatigue, strength and reliability assessments are left for future work.