Study On Complex Aerodynamic Admittance Functions And Refined Analysis Of Buffeting Response Of Bridges

The research status of aerodynamic admittance functions (AAFs) was first reviewed and problems in the research were issued in the thesis. Aerodynamic admittance functions (AAFs) are one of the important aerodynamic parameters affecting buffeting response of long-span bridges. The development of rational AAFs is an important research field towards the refined/improved buffeting theory. This thesis is concerned with modeling and identification of AAFs from wind tunnel testing data for thin plate section and several types of bridge cross sections, the proposal of refined buffeting theory formulated taking into account both the developed AAFs and measured coherence/correlation of buffeting forces in frequency domain and in time domain, and the experimental validation of refined buffeting theory with the use of testing results from the full-scale aeroelastic model of a bridge in wind tunnel. Wind tunnel testing, numerical simulation and theoretical formulation are used in this study. In Sum, the main contents are concluded as follows.(1) After a careful and detailed review of the current research status concerning aerodynamic admittance functions, including the origin, theoretical and experimental study, testing setup and empirical formula of AAFs, issues are pinpointed and the content and objectives of the present research are confirmed.(2) The forces acting on thin airfoil are re-examined in depth to provide the physical meanings and formulations of aerodynamic admittance functions and to lay down the theory foundation for developing the AAFs of other bridge sections. The aerostatic coefficients of thin airfoil are described. The theoretical aerostatic coefficients of ideal thin plate cross section at different wind attack angle are then derived. The derived coefficients provide the basis for wind tunnel testing and numerical simulation studies of thin plate section addressed in the third and fourth chapters.(3) An active turbulence generator technique is developed to generate the longitudinal and vertical components with a harmonic frequency at one time. A frequency-by-frequency method of identifying complex AAFs (CAAFs) is developed and formulas of CAAFs are derived. The method is validated the simulated'experimental'data.(4) The active turbulence generator is devised following above philosophy and generating the oscillating longitudinal and vertical velocity components with a single frequency. The generator has the merit to provide deca-meters order of the turbulent integral scale of the generated harmonic oscillating wind field, which overcomes the difficulty to generate wind field with large turbulent integral scales. A horizontal setup of measuring force with double force balances is developed and used to measure the aerodynamic force acting on sectional models suspended in wind tunnel. Making use of experimental data, six CAAFs are successfully identified. CAAFs of the thin plate section and three kinds of other bridge section models are obtained. Many significant results and suggestions are obtained by comparing the experimental results.(5) Based on the frequency-by-frequency identifying method, the investigations of CAAFs using computational fluid dynamics (CFD) technique are carried out in the Chapter 5. CAAFs are investigated using the numerical simulation technique of CFD. The numerical results are compared with the experimental results and many significant results are obtained.(6) A frequency-domain method taking into account the modification of AAFs and coherence functions of buffeting forces is presented for analyzing the buffeting response of cantilever structures with twin-legged high piers. Taking Xiaoguan bridge as an example, the displacement responses and the internal forces at the bottom of the left pier of the bridge are obtained. The contributions of each component of the aerodynamic forces and of each part of the structure to buffeting response of the bridge are investigated. In addition, effects of AAFs and coherence of buffeting forces are studied on the buffeting response of the bridge.(7) A new wavelet method of simulating wind field is presented. The method can simulate the self-similarity and intermittency of turbulence. Up to now, the method can only simulate one-dimension and single-variant wind field and is worth of further research.(8) A time-domain method is formulated also considering the modification of CAAFs and coherence functions of buffeting forces. The buffeting response of cantilever structures with twin-legged high piers is now performed using time-domain method. It validates the consistency of the frequency- and time-domain methods by comparing results obtained from the two methods.(9) Aeroelastic model experiments of cantilever structures with twin-legged high piers are carried out in wind tunnel. The experimental results are compared with analytical results and validate the correctness of time-domain and frequency-domain methods presented in this thesis. (10) The time-domain method for buffeting analysis of bridges presented in Chapter 7 is extended to analyze buffeting response of Donghai Bridge. The results obtained from the present method of Chapter 7 are compared with the results obtained the results reported in the literature. The closeness of the two sets of results is observed.