Optimizing mooring tethers to minimize wave-induced structural responses in submerged floating tunnels

This study investigates optimal mooring tether designs for submerged floating tunnels (SFTs) to mitigate dynamic structural responses under wave loading. Four configurations were assessed through hydrodynamics-based numerical simulations in ABAQUS-AQUA, enabling direct comparison of motion control performance. The doubly-inclined tether system exhibited the highest efficiency, and its motion control mechanism was experimentally validated. Based on these findings, an integrated mooring design process incorporating multiple criteria is proposed. Recognizing the difficulty of determining optimal design parameters solely through numerical simulations, a simplified analytical method is introduced as an efficient alternative and validated against simulation results. By applying this method, an optimal doubly-inclined tether configuration was obtained, with an outside tether inclination angle of 27.7°, determined considering maximum and minimum tether stresses, and a spacing of 58 m between tethers, governed by fatigue. As these parameters vary with environmental conditions, their final determination should follow the proposed design process for practical implementation.