Assessment of regular and earthquake-induced wave hydrodynamic tests of moored and end-fixed submerged floating tunnels

Submerged floating tunnel (SFT) is a new type of fully immersed sea-crossing structure for future traffic design, which has a high application prospect in complex bay environment. During the service lifespan, SFTs have the risk of wave impact. Therefore, to ensure safety and stability of the SFTs, hydrodynamic tests of a 1:60 scaled model were carried out in a large pool with underwater vibration table, where data on acceleration, roll, pitch rotation, yaw rotation, displacement, variation table and cable tension were collected. Comprehensive investigation was conducted to explore the excitation effects and hydroelastic responses of the model under regular and earthquake-induced waves with different immersion depths along with the modal characteristic analysis. The results show that the natural frequency of the SFT is significantly influenced by the angle of the cables. As the angle increases, the vertical stiffness of the system also increases, which consequently raises the natural frequency of the structure. According to hydrodynamic analysis, shallower the depth of the SFT, the more it hinders the propagation of waves, resulting in subsequent wave attenuation but aggravating structural responses. Furthermore, under regular and earthquake-induced waves, harmonic resonance can be triggered. The acceleration, roll angle, and cable tension undergo the most significant changes at the mid-span section. The increase in cable tension on the upstream side exceeds the decrease in tension under higher frequency wave due to wave impact force. There are discrepancies in angle responses among the cross-sections and the mid-span section demonstrates larger roll angles and smaller pitch and yaw angles, leading to phase angle deviations among the three variations. For earthquake-induced waves, more pronounced structural responses result from greater seismic acceleration amplitude and shallower immersion depth. And the response relationship between sway and heave, as well as the periodic variations in mooring cable tension and angle, remains consistent with that under regular waves. This consistency underscores that the dynamic behavior of the SFT is primarily governed by the intrinsic structural properties and hydrodynamic interactions, rather than the specific nature of the wave excitation.