## 5 Conclusions  
The submerged floating tunnel (SFT) is a new structural solution to waterway crossings. Despite some valuable research having been accomplished, no SFT has been constructed in the world up to now. For the realization of SFT projects, the global performance in extreme environmental conditions needs to be properly evaluated. This study evaluates the displacements and internal forces of an SFT subjected to hydrodynamic and seismic loadings. The SFT tunnel was modeled by 3D beam elements; the mooring cables were modeled by truss elements; the ocean waves and currents were modeled by Airy wave theory. The SFT response subjected to hydrodynamic loading was evaluated using three different mooring cable configurations; the suitable mooring cable configuration was then used for further evaluation. A comparison of response envelope curves for static, hydrodynamic and seismic loadings was presented to evaluate the most effective structural response of SFT.  
Based on the present study, the following conclusions can be drawn:  
Figure 12: SFT dynamic response comparison at mid-span (Section B): (**a**) \(Y\)-displacements; (**b**) bending moment M\({}_{\mathrm{Z}}\); (**c**) \(Z\)-displacements; and (**d**) bending moment M\({}_{\mathrm{Y}}\).  
* The static response can provide a benchmark for decision-making on mooring cable arrangements and configurations for the preliminary design. However, the static analysis underestimates the responses in comparison to those of dynamic analysis
* The SFT moored by tension leg mooring cables was least effective, because of lesser horizontal stiffness, and the SFT moored by such mooring cables undergoes extreme displacements in the transverse direction as compared to the one moored by inclined mooring cables. The SFT moored by a combination of tension legs and single inclined mooring cables was effective for moderate environmental conditions. For severe environmental conditions, the SFT should be moored either by a combination of tension legs and double inclined mooring cables or only by double inclined mooring cables.
* For hydrodynamic analysis, the transient motions of SFT were small and decayed quickly, and the steady-state motions mainly governed the structural response of SFT under the prescribed damping conditions. In the case of the seismic analysis, the transient motions are more pronounced as compared to the hydrodynamic response.
* In the hydrodynamic analysis, the vertical response of SFT was very small and mainly attributed to gravity and hydrodynamic forces; while the transverse response was very large for seismic analysis. The transverse displacements and internal forces were found to be larger than those of the vertical direction, which showed less restraining and lesser mooring cable stiffness in the transverse direction.  
The Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education, Science and Technology (NRF-2015R1D1A1A09060113), supported this research. The authors wish to express their gratitude for this financial support.  
[PERSON] supervised the research. [PERSON] contributed the idea, performed the numerical simulations and wrote the manuscript. [PERSON] helped with the simulations and the writing of the manuscript.  
The authors declare no conflict of interest.