Dynamic Response Analysis Of Submerged Floating Tunnel

Though submerged floating tunnel (SFT) is an innovative concept, it has gained more and more attention worldwide for its advantages in the crossing of deep water. SFT basically consists of a tunnel floating in the water, due to positive net buoyancy, at some convenient depth and fixed to the seabed by means of a suitable anchoring system, encompassing tethers or tension legs. Thus, it can be seen that the SFT is much more prone to undergo significant oscillations due to dynamic effects than traditional tunnels.Vibration of submerged floating tunnel may be expressed as combination of global and local modes. Global mode is defined as the vibration of the tube in which the tethers are treated as elastic tendons with no independent transverse motion, while the local mode is that of a tether fixed at the two ends. In this paper, we dealt with dynamic response of submerged floating tunnel from two aspects: global mode and local mode. Taking the frequent earthquake in China and importance of tether vibration into account, the global dynamic response of submerged floating tunnel under the earthquake and the tether vibration under parametric excitation and forced excitation were performed. Moreover, a preliminary study on the passive control of tether vibration was presented. The main contributions are summarized as follows:(1) This paper introduced the concept, features, development of submerged floating tunnel and stated the state-of-art of its structural analysis from several aspects such as tube, anchor system, load and model experiment. Also, the development direction and key problems that need to be solved were presented. All of these are benificial to further research and new standards.(2) Until now, no submerged floating tunnel has been built yet. Thus, model experiments are very important to dynamic response of submerged floating tunnel. To simulate the real situation of coupled submerged floating tunnel-water, the first model experiment of submerged floating tunnel under the earthquake at home and abroad was performed on the large-scale underwater shaking table in Dalian University of Technology. According to the experimental phenomena and data, the seismic characteristics and main effect factors for dynamic response of submerged floating tunnel were analyzed.(3) Based on the potential fluid theory, seismic response of submerged floating tunnel was studied by numerical analysis. To ensure the validity of numerical model, firstly, numerical model close to the seismic response model experiment was set up. The results were compared with those of model experiment. It can be seen that the numerical results are basically identical with those of shaking table test. Numerical model adopted is effective for dynamic response of SFT. Secondly, according to the parameters of designed SFT at home and abroad, modal analysis and main effect factors for dynamic response of submerged floating tunnel were analyzed by numerical method.(4) To analyze dynamic response of tether under parametric excitation, a theoretical model of coupled tether-tube was developed. Also, the corresponding vibration equation is set up. By Galerkin method and Runge-Kutta method, the possibility of large-amplitude vibration of submerged floating tunnel tether under parametric excitation was on discussion. Since the tether sag effect is very importance, sag in this paper was considered by two methods—convenient equivalent elastic modulus method and parabola method that may reflect the sag effect.(5) Taking the tether of submerged floating tunnel as a beam with strain, the equation of vortex-induced vibration of tether was set up. Multi-order vortex-induced nonlinear vibration of submerged floating tunnel tether subjected to current was discussed. The importance of its high-order vortex-induced nonlinear vibration was illustrated in numerical examples. In addition, to simulate the parametric excitation accurately, a nonlinear tether-tube model of submerged floating tunnel was proposed. Under this condition, the transversal oscillation response of tether under vortex-induced vibration and parametric vibration was analyzed.(6) Taking the system that consists of tether and visco-elastic dampers as research object, the vibration equation of tether and visco-elastic damper was set up considering tether sag effect. By means of Galerkin method, the partial differential equation was transformed into a set of ordinary ones. Subsequently, maximum damping ratios and corresponding optimal damper coefficients were obtained by complex eigenvalue analysis.