The Models For Hydrodynamic Analysis Of The Submerged Floating Tunnel Under Wave And Current Action

Submerged Floating Tunnel is a new type of traffic structure across straits,river and lake.This type of tunnel is characterized by the fact that it crosses both banks instead of being buried or placed above the riverbed of the tunnel,and is suspended in a structure.It is fixed at 20-50 m below the surface of the water,mainly composed of a tunnel tube body suspended in a certain depth underwater,an anchoring device that restricts excessive displacement of the tube and a revetment section that connects with the two banks,and it balances the dead weight by the tension of the anchor cable and the buoyancy of the fluid.Floating tunnel has the advantages of flexible layout,cost saving,pollution reduction and environmental protection.All the potential advantage above makes the floating tunnel an important subject for scholars to study.The floating tunnel is located below the horizontal level,and the environment is mainly wave and water flow.Therefore,it is particularly crucial to research the wave force and water flow force of the floating tunnel.The floating tunnel can be considered as an elastic body and it will cause resonance on condition that its natural frequency is close to the shedding frequency of the vortices generated alternately from the tunnel surface on both sides when the fluid flows through the floating tunnel,which results in large amplitude vibration cross flow or downstream,so it is also imperative to research vortex-induced vibration of the floating tunnels.In summary,the main research work of this paper is as follows:Considering that the slenderness ratio of the floating tunnel is relatively small,the diffraction theory is used to calculate the wave force on the floating tunnel.Generally,most scholars regard the floating tunnel as a structure with large slenderness ratio and use Morison equation to calculate the wave load of the floating tunnel,while this paper considers the case where the tunnel slenderness ratio is relatively small,and the tunnel surface boundary are divided into units based on the simple Green function boundary element method,after which the integral equation is discretized by introducing shape functions and Gaussian integration,and then solved after assembly.The influence of water depth,placing depth and radius on wave characteristics of suspension tunnel is analyzed.The finite element model under the coupling effect of the floating tube-anchor cable is established to solve the natural frequency of the tunnel.Based on the finite element method,the tunnel is dispersed into multiple beam elements along the length direction,and the element characteristic equation of each element is analyzed.According to the stiffness definition-the mooring force under unit displacement,the mooring force along the direction of the anchor cable is decomposed into two coordinate axis directions to obtain the linear stiffness matrix of the anchor cable.And,the element stiffness matrix is assembled to obtain the total stiffness equation according to the equilibrium conditions of the forces at the nodes.The eigenvalue method is used to calculate the natural frequency under the action of anchor cable in the case of no damping.The numerical results of this model are compared with analytical solutions to verify the reliability of the model.Based on SHEAR7,the VIV model developed by Tang was used to analyze the vortexinduced vibration response of submerged floating tunnel under the tube-anchor coupling effect.The excitation mode of the tunnel is judged by a given threshold,while the excitation length of each mode is judged by the critical value of the reduction speed.Although the vortex-induced vibration response of the tunnel is dominated by the excitation modes,it is the result of the joint participation of each mode.It is analyzed for the vortex-induced vibration response of the tunnel tube-anchor cable under the single-mode locked state and the multi-mode unlocked state,for which the effect of water velocity on the vortex-induced vibration response under constant flow is considered,and the displacement and acceleration response of the vortex-induced vibration in shear flow are also included.