Study On Characteristic Of Flow-Field Around Submerged Floatig Tunnel And Fatigue Damage Of It’s Cable

Submerged floating tunnel is abbreviated to SFT, Also known as Archimedes Bridge. As an underwater structure, wave and current load are the major environmental loads. Shape and dimension of SFT’s Cross-sectional have an important influence on fluid force on the surface of SFT. Lift coefficient, drag coefficient, and St on SFT with different sections form have large discrepancy, which has an influence on the stress state of the tube and support system. Some research of hydrodynamic on SFT has carried out in the world. But more study methods are based on approximate Morison equation and there are little systematic research results. In the dissertation, the research object is cable-stayed SFT.Hydrodynamic characteristics of SFT’cable has a major import on stability and reliability of tube and durability of Cable. Previous studies on cable’VIV more adopted "lift oscillator" model and the vortex-induced force on cable was calculated by Van-der-pol equations. Lift oscillator model which is an approximate mathematical model for the calculation of cable’VIV does not have universality. Beyond that,Support system fatigue damage is an important part of SFT system reliability,however, the study on reliability and durability of cable and other support systems is almost empty.in the dissertation,the hydrodynamic problem on SFT in the uniform flow, the vortex induced vibration phenomenon of SFT’cable and fatigue damage mechanism of cable have been conducted in-depth research. This dissertation specific contents are as follows:(1) Using finite volume method to discretize the Naviar-Stokes equations, the article analyses the flow field around different cross-section of SFT, In order to verify the feasibility of this article turbulence model and numerical simplification techniques, first the eddy viscosity model, large eddy simulation and Reynolds stress model are used to calculate flow field around circular section(streamlined structure)and square section(obtuse-type structure),then above calculation result such as life coefficient, drag coefficient Stouhal number and pressure distribution on the surface of SFT also are compared with model experiments and other number simulation results. At last the various turbulence models are analyzed to calculate flow around the tube in different Reynolds number and the optimal turbulence model is acquired. Simultaneously, grid model and parameter values of the reliability are verified.(2) Using the Reynolds stress model to simulate the flow field around SFT, considering different velocity condition, different section dimension and different section shape, some results such as life, drag, Stouhal number and pressure distribution on SFT have been calculated. Considering the sharp corner influence, two typical form of sharp corner section and streamline section with different aspect ratio influence on the results of the above calculation have been analyzed, meanwhile the calculation results with same aspect ratio and velocity condition but different section shape has been compared and analyzed and some beneficial conclusions are gained(3) The supporting cable of SFT has excessive slenderness ratio which leads to greater flexibility of SFT structure. Vortex-induced vibration is a basic fatigue failure factor of such flexible structure. The dissertation researches fluid-structure interaction dynamics based on CFD numerical simulation of the finite volume method and numerical integration of the structural dynamic control equation, Structural dynamic module is written to the commercial FLUENT software by user define function interface and the fluid-structure coupling analysis is realized by motion mesh. Dynamic parameter such as vortex induced amplitude and vibration frequency in different velocity condition is calculated, it is discussed that the effects of cable mass ratio, damping ratio, inlet velocity and whether consider cable streamline motion on cable Transverse vortex induced vibration.(4) Cable fluid-induced fatigue failure is an important part of SFT reliability research. The research method of fluid-induced fatigue failure of flexible structure is mainly numerical simulation based on CFD and the quadrate empirical function method. The article analyses the fatigue damage of marine structure by modal quadrate technology. It is assumed that the long-term ocean current and wave conditions meet zero mean narrowband random process and structure peak stress meets Rayleigh distribution. The flexible structure fatigue damage along the longitudinal direction of the distribution is attained by fatigue cumulative damage theory. then flexible structure fatigue damage distribution is calculated in step current and shear current, the calculation result coincides with other modal test result well, thus this further verifies the feasibility of the present algorithm.(5) The effect factors of cable vortex-induced fatigue damage which are cable length, cable density, and pre-tension and velocity condition are discussed by using the present modal superposition method procedures. The result shows that:the velocity condition has the greatest impact, it was followed by cable length, pre-tension and cable density. With velocity shear rate increases, the largest fatigue damage of cable evidently decreases; with cable length or density increases gradually, cable greatest fatigue damage also increases gradually; with cable pre-tension increases, the largest fatigue damage of cable gradually decreases.