The optimization design for the truss substructure of the novel truss-type submerged floating tunnel using the topology optimization method

The truss-type submerged floating tunnel (SFT) represents an innovative design that combines jacket platform technology with conventional SFT concepts, delivering enhanced dynamic stability, accelerated construction timelines, superior structural efficiency, and improved maintainability. However, developing systematic optimization methodologies for truss-type SFT remains crucial to achieve an optimal stiffness-to-weight ratio, minimize dynamic responses under wave loading, and ensure long-term structural reliability. This study presents a four-stage optimization methodology for truss-type SFT: (1) buoyancy-to-weight ratio (BWR) optimization, (2) shape optimization, (3) topology optimization, and (4) size optimization. This sequential approach combines multiple optimization techniques to achieve comprehensive performance enhancement, addressing the limitations of conventional isolated optimization methods. The results reveal substantial performance enhancements: optimizing the BWR to 1.5 reduces sway and roll motion by 12.3 % and 13.1 %, respectively. Shape optimization with an 80^∘ angle of the leg relative to the seabed and a 2.5 truss system cross-section aspect ratio achieves optimal balance between motion control and stress distribution. Topology optimization yields 15.7 % and 25.4 % reductions in sway motion and maximum von Mises stress, respectively. Subsequent size optimization further improves structural stiffness across all degrees of freedom. This comprehensive methodology provides valuable design insights for truss-type SFT, enabling optimized structural performance.