Aerodynamic Analysis Of Slender Structures In Turbulence Flow

Wind-resistant analysis of bridges has now become an important problem because of the rapid developments and increasing applications of long-span bridges. The wind-induced aerodynamic forces on structures including self-excited aerodynamic forces and forced aerodynamic forces, the resulting flutter and buffet are some focal points to be investigated. The cross sections of long-span bridges are usually classified to blunt bodies, around which the flow distributions are very complicated. As analytical expressions of aerodynamic forces are not available, therefore the wind tunnel test is the most effective way to investigate wind-induced vibrations of long-span bridges. Unfortunately, since the actual flow distribution conditions around the bridges can hardly be expressed comprehensively in a wind-tunnel laboratory, and it has been found by comparisons that the wind tunnel test results are quite divergent even for identical models and testing conditions. Clearly, it is not sufficient to investigate wind-induced vibrations of long-span bridges only by means of wind tunnel tests.Due to the development of computers, much computational work with computational fluid dynamic method (CFD) has been undertaken in the investigations of wind-induced vibrations of long-span bridges. But the research of aeroelastic problems of wind effect on bridges with CFD has its own difficulties, such as the flows around bridges are unsteady separated flows with high Reynolds numbers and the wind-structure interaction effects between winds and bridges cannot be neglected. Also due to the limitation of computational ability and methods, most investigations on wind-induced bridge vibration are two dimensional, and the knowledge about the turbulent flow is still quite limited.In view of this, this doctoral dissertation uses the CFD method combined with the block-iterative coupling method and arbitrary Lagrangian-Eulerian mesh control method to investigate the wind-induced vibrations on long-span bridges. In order to analyse the wind-structure interaction problems of long-span bridges in turbulence flow, high Reynolds numbers are chosen, turbulence models are introduced and multi-grid method is adopted. The analysis processes are based on the computations of aerodynamic parameter values and the investigations of the flow characteristics around different structures, from two dimensional models to three dimensional models, and from streamlined bodies to blunt bodies. An effective CFD method to study wind-structure interaction effects on different structures in turbulent flows is established. The main research contents of the full paper are as follows: 1. CFD method based on the block-iterative coupling method and arbitrary Lagrangian-Eulerian methodTo study aeroelastic problems according to fluid-structure interaction analysis, a novel CFD method based on the block-iterative coupling method and arbitrary Lagrangian-Eulerian method is proposed. The flow analysis and structure analysis are coupled through arbitrary Lagrangian-Eulerian current coordinate method. The analysis process uses self-developed program system DDJ-W and a solver of the commercially available CFD code ANSYS-CFX.2. Construction of high performance parallel computing software and hardware systems to analyse complicated turbulent flow characteristics.A high performance computing system with low cost is proposed, which can be widely applied to the analyses of complicated turbulent flow characteristics. An open source operating system named Centos which has excellent parallel computing performance and DRB1parallel structure are introduced. This computing system is based on the PVM algorithm and the use of desktop hardware. This effective and flexible high performance computing system is the necessary hardware foundation of three dimensional wind-structure interaction analysis of long-span bridges in turbulent flows.3. Numerical analysis of a streamlined structure with the two dimensional CFD methodNACA0012airfoil is chosen as a representation of streamlined structures to verify the present CFD method for two dimensional numerical simulations. A new mesh control method is used to model the flow-structure meshes of NACA0012airfoil and the k-ω SST turbulence model is adopted. Firstly, numerical wind-structure investigation of an airfoil structure, which is fixed initially and has the same chord direction as that of the flow velocity, is performed. Its aerodynamic force coefficients and flutter derivatives are computed and compared with the wind tunnel test results or theoretical values. The flow characteristics is analysed through computer pictorial visualizations. Then, extended simulations of the airfoil are performed for different initial conditions such as the angle of attack, forced vibration amplitude and Reynolds number. The aerodynamic parameters of the airfoil are computed and the aerodynamic characteristics are analysed.4. Three dimensional CFD numerical analysis of wind-structure interaction problems of long-span bridges in turbulence flowA three dimensional CFD method based on the block-iterative coupling method with the newest DES turbulence model is used to analyse the wind-structure interaction of long-span bridges in turbulence flow. The aerodynamic coefficients and flutter derivatives of the typical and special sections of five long-span bridges were computed and visualized. The computed aerodynamic parameter values are compared with the wind tunnel test results and those based on the Discrete Vortex Method (DVM) in order to show the validity of the present three dimensional CFD method.5. Three dimensional aerodynamic analysis of a U-shape beam with wind tunnel test and CFD methodThe wind tunnel test of a U-shape beam which has poor aerodynamic stability was designed and made to measure its aerodynamic parameter values. Then both two dimensional and three dimensional CFD methods were used to investigate its aerodynamic characteristics. The CFD-based results were compared with the wind tunnel test-based results to validate the effectiveness of the present three dimensional CFD method for structures with poor aerodynamic stability. This work verified the completeness of the present analysis method of wind-structure interaction of different structures in turbulent flow in view of methodology.6. Wind-induced random vibration analysis of different structures with pseudo excitation method and CFDThe wind-induced random vibration analyses of a composite wing and the Tsing Ma bridge girder sections in Turbulent flow were performed using a highly efficient method for random vibration analysis-PEM (pseudo excitation method) and CFD technique. In order to obtain unsteady aerodynamic parameters of the structure accurately, the present CFD method is used to replace the wind tunnel test. The PEM converts the computations of power spectral density functions of the structure stochastic responses to the analysis of the dynamic responses under deterministic loads and so improves the computational efficiency considerably.