Dynamic Response Analysis And Experiment Of Submerged Floating Tunnel Based On Fluid-Structure Interaction

Submerged floating tunnel(SFT) is a new traffic structure across long waterway with advanced technology, environment protection and according with sustainable development. The research and analysis of vortex-induced vibration under current and wave, seismic response and boundary conditions of the revetment structure for SFT are very important. In this paper, the vortex-induced vibrations(VIV) and seismic response of SFT were studied, which is funded by the National Natural Science Foundation of China. The characteristics about the cable and tube coupling system of SFT, the Fluid-Structure Interaction (FSI) VIV of cable, the horizontal seismic response of SFT and the hydrodynamic load on tube under vertical seismic were investigatived, considering the fluid-structure interaction. The main research contents are as follows:(1) The differential equations of the cable and tube coupled motion are derived by using Hamilton principle, taking the coupling effect between cable lateral vibration and tube vertical vibration into account, based on a simplified tube-cable system. On this basis, the tube-cable coupling vibration response of a SFT under the vortex-induced force was analyzed by setting different design parameters and conditions.(2) The free vibration in the water and VIV in uniform flow have been calculated by using the separate coupling method (numerical method) and considering the fluid-structure interaction, based on structural dynamics theory and hydrodynamics, in the background of Qiandao Lake SFT design. The free vibration frequency and fluid linear damping ratio of cable in the water was obtained. The in-line and cross flow amplitude, the drag coefficient and lift force coefficient under various reduction rates were analyzed.(3) The first section model experiment of SFT in China was carried out in the stormy stream structure integrated sink in Zhejiang University Architecture Laboratory, to approximately simulate the FSI VIV of cables of Qiandao Lake SFT. The inertial force coefficient and linear fluid damping ratio of cable in still water, the in-line and cross flow amplitude, the drag coefficient and lift force coefficient under various reduction rates were measured. Moreover, influence of different inclination angles and flow directions on the vortex-induced vibration of cables were tested and analyzed.(4) The vibration suppression methods were proposed by reference to the marine riser vibration suppression measures, and three vibration suppression devices(three strakes, three control rods and fairings) were designed. The effect of different inclination angles and flow directions to vibration suppression was investigated by using model experiments, and the future vibration suppression device selection of SFT was suggested.(5) The seismic response characteristics of SFT in the lateral earthquake were researched, considering the impact of the geotechnical properties around the revetment structures to the boundary conditions. The displacement, bending moment and torque of tube and cables tension were calculated combined with the seabed geotechnical nature in the eastern ocean, by using large mass method, based on the Messina Strait SFT option. The effect of the revetment length Ish, cohesive shear modulus G, cable inclination angle a, tube weight ratio η and seawater hydrodynamic coefficients (CD and Cm) and other parameters were analyzed.(6) The concept of hydrodynamic load-the force on the surface of tube generated from water affected by the earthquake excitation, was put forward for the tube and cables of SFT in ideal fluid layer. The equations and boundary conditions to calculate hydrodynamic load on SFT tube in ideal fluid layer under the earthquake P-wave were derived with the wave theory, considering the influence of the upper and nether water and the stiffness and spacing of cables. By the parameter study, the affection of the upper seawater thickness h, the P wave frequency value co and incident angle α, the cable stiffness Kc and the spacing L to the value of hydrodynamic load have been analyzed.