The Study On Responses Of A Submerged Floating Tunnel Subjected To The Wave And Current

The submerged floating tunnel (SFT) is an innovative traffic structure used tocross a strait, a bay, a fiord, a lake or other appropriate waterways. The mainstructural members of an SFT are submerged connected tubes, which are kept atsome depth below the water surface by the balance between the downward load andthe buoyancy force and with the aid of a specialized support system. The advantagesof the SFT are1. The total length of an SFT is noticeably shorter than that of any ordinary submarine tunnel;2. Lower environmental impact and improving the environmental protection;3. Relatively higher degree of freedom in site selection.These benefits are so obvious that it rendered the SFT becoming increasingly a new researching task in tunnel specialty.The action of an SFT forms a new conception in tunnel design. From the angle of surroundings and loads the condition of the SFT is obviously different from that of a conventional tunnel. As a result of directly situated in the natural environment with wave and flow actions the unusual loads produced by these actions constitute one of the major surrounding forces exerted on the SFT. Moreover, the wave action, which varies as a function of time, will cause dynamic effect, and the latter, as everyone knows, tends to increase the stress and to destroy the long-term stability of the structure. On the other hand, because of the attenuation of wave action with the increasing of depth under water surface, the wave action on an SFT may be less than the flow action, and the latter will exert a considerable horizontal force on the SFT. In addition the deflection of an SFT section under the wave and flow actions is very small, but owing to the great length of the submerged tunnel the shape of the structure will change fairly, even it is possible to appear large nonlinear displacement and rotation. There will arise harmful influence on the safety and stability of the SFT structure. Therefore, for structures of this kind, dynamic response should always be the focus of attention either in designing stage or in operating stage.In this dissertation the main study aimed at the interaction of the wave-current effect and the SFT. The contents of the study consist of two parts. In the first part it isstressed on the study of the static and dynamic response of an SFT to the combined actions of the wave and current. In the second part the main task is set on the analysis of the dynamic response of vortex-induced structures.The concrete tasks accomplished consist of the following contents.1. On the basis of diffraction theory the wave loading on an SFT was solved by the source distribution method; and the fluid force acting on the SFT was solved with the Morison equation.2. By employing CR formulation of 3-D spatial beam element and considering the interaction of the solid and fluid; a finite element model and relative calculating process to analyze the static and dynamic responses of the SFT structural system were established.3. On the basis of above-mentioned model and calculating process; in accordance with different sea conditions; distinct types of tunnel sections; various submerged depths and support systems a series of comparative analyses were carried out.4. The mechanism of vortex releasing and the basic concept of vortex-induced oscillation of structure were explained; and current methods used to solve the vortex-induced oscillation problem were compared.5. According to the summary of current methods to solve the vortex-induced response problems; a 2-D analyzing method to approximately evaluate the dynamic response of the vortex-induced structures was proposed. By this method; under the condition of "lock-in" frequency; comparative evaluation of the dynamic response of vortex-induced SFT and its support structure were carried out.