Numerical Analysis And Experiment Research Of Submerged Floating Tunnel Subjected To Wave And Current Effects

Submerged floating tunnel is a new symbolization of crossing tunnel conception. Submerged floating tunnel generally consists of tube structures floating in given depth below free surface, cables linked with the anchoring foundation and structures connecting the bank sides. This type of tunnel is not constructed in the middle of stratum or through stratum. It is surrounded with water, which make it different from the traditional tunnels. The submerged floating tunnel is balanced with the self-gravity and buoyant forces and support system in the given depth. Considering many merits in environment protection, social benefits, economic benefits, construction costs and etc, submerged floating tunnel is becoming a new research subject in the tunnel profession. There are potential application values in the construction of connecting structures between the islands and the mainland, the bay crossing channesl and the offshore buildings.Considering long extension of the submerged floating tunnel in the axial direction, geometric nonlinearity is expressed obviously. In the condition of large displacement, the interaction between structures and fluid can not be avoided and wave and current force is also changed nonlinearly. In the action of gravity, buoyant force, wave and current force and support system, large rigid displacement and rotation may be produced. The reliability and stability of submerged floating tunnel structures is influenced seriously. Though the submerged floating tunnel has not been applied in the practical construction, the irrelevant research has been carried on for thirty years in many countries and the scientific efforts was afforded in domestic. Little advance was achieved in integral and system research on the submerged floating tunnels.Given the characteristics of the submerged floating tunnels, the analysis in this article was majored in three parts. It was detailed in the flow around submerged floating tubes, static and dynamic response of submerged floating tunnels subjected wave and current forces, sectional model experiment research. The detailed contents in each part were described as following:(1) Flow field around the submerged floating tunnel with large scale cross section in super high Reynolds number was simulated using RNG K-εturbulent model with CFD module of ADINA program. The pressure coefficient and drag coefficient of different section type in steady state were obtained as well as drag coefficient and lift coefficient in impulsive motion and Strouhal number. The variation of the hydrodynamic parameters with different geometric configuration and aspect ratio was analyzed. With the general comparison of the hydrodynamic parameters, each type of cross section was evaluated and guidelines for the section design were presented. The parameters required in the static and dynamic analysis of the submerged floating tunnels were offered. Thus, inaccuracy of parameters can be avoided.(2) Simplified method for calculating the wave and current force with Morison formula was introduced. The parameters influencing on the wave and current force were analyzed such as depth of structures, depth of sea, current velocity and scale of cross section.(3) In the conditiion of large displacement, the interaction between the structures and fluid can not be ignored. The wave and current forces change nonlinearly. Nonlinear dynamic analysis model considering the interaction of submerged floating tunnel structures and fluid was constructed with nonlinear calculation method of the wave force and the lateral lift force. Based on the appropriate discrete approximation, the solution procedure was implemented with the secondary development of the ANSYS program. The difference of the response in the nonlinear model and the linear model was verified with the numerical dynamic analysis of single span submerged floating tunnel structures. It is proved that the nonlinear model is the mandatory requirement in the dynamic analysis of the submerged floating tunnel. The parameters influencing on the response of submerged floating tunnel were analyzed with nonlinear model such as the length of structures, the scale of cross section, the additional permanent load, the depth of structures, the current velocity. Considering the reliability and stability and economic benefits of the structures, the primary principles for the submerged floating tunnel structures were put forward.(4) In order to evaluate the influencing of cable on the submerged floating tunnel structures, the dynamic response of the cable subjected current force was numerical simulated. The parameters influencing on the lateral displacement and axial force of the cable were analyzed such as the pre-tensile force, the current velocity, the cable length, the scale of cable cross section.(5) Considering the characteristics of the submerged floating tunnels, the tubes were simplified into the spatial beam element. The cables were simulated with link element and the longitudinal and perpendicular stiffness was considered. The submerged floating tunnel was constructed with the herringbone beam model and the solution was obtained with nonlinear dynamic method. The parameters influencing on the static and dynamic response of submerge floating tunnel structures with the circular section and the straight line body were analyzed such as the longitudinal and transverse layout of cable, the cable length, the layout angle of cable, the layout distance of cable, the pre-tensile of cable. Taking the submerge floating tunnel with the circular section and the lopsided layout of the cables as example, the parameters influencing on the static and dynamic response of the structures were analyzed such as the curvature of the curved and the invert submerged floating tunnel. The tube junction and the waterfront junction element was created with the modification of the user defined element. The bending rigidity and the distribution of junctions influencing on static and dynamic response of the submerge floating tunnel were analyzed. In the view of stability and the security of structures and the economic benefits, the feasibility of application in the construction was analyzed.(6) The spatial mechanical characteristics of the submerged floating tunnel structures were extraordinary. The special phenomenons can be produced such as bending, twisting, distortion and warping. It can not be analyzed with herringbone beam model. According the work circumstance of the submerged floating tunnel, the submerged floating tunnel test platform was constructed. The segmental model experiments of submerged floating tunnel were carried on. The spatial stress distribution of the segmental model and the axial force of cable were analyzed.