Numerical Approaches And Their Applications To Wind Effects On Bridges

With the immense leap in computational speeds in the recent past, numerical experiments via Computational Fluid Dynamics are fast maturing as a viable complement, if not an alternative, to wind tunnel investigations to study the various wind effects on bridges. Based on numerical approaches, the present study focuses mainly on two sections, one is aeroelasticity of bridge, the other is aerodynamic characteristics of bridges and vehicles in crosswind. It should be generalized as follows:1) The two-dimensional governing equations in deforming domain are derived by using an Arbitrary Lagrangian-Eulerian(ALE) coordinate system for the description of both the structure and the fluid in computational domain. The moving grid technique is adopted to simulate the fluid fields around the rigid body such as bridge girder cross-sections.2) A novel second-order Projection method is employed, for the first time, to efficiently solve problems governed by unsteady, incompressible Navier-Stokes equations for the description of aeroelasticity of rigid body. With different temporal and spatial treatments to the convective terms, this method has entered into both the Finite Different Method(FDM) and the Finite Volume Method(FVM), then, multigrid algorithm is employed to speedup the convergence of the Possion's equation for pressure, all this make it possible to simulate incompressible flow efficiently and quickly.3) The forced oscillating procedure is used to compute flutter derivatives of both the ideal flat plate and the thin plate, with the discretization methods FDM and FVM, respectively. Results of the ideal flat plate are closed to the Theodorsen's theoretic solutions. Results of the thin plate match both the Theodorsen's theoretic solutions and results from wind tunnel tests by using the Forced Vibration Technique(FVT).4) The FVM code is employed to compute flutter derivatives and onset wind speeds for flutter of the Humen Bridge in China. Numerical results of the Humen Bridge are compared to data obtained from section model tests in wind tunnel by using the FVT and the Free Vibration Method, better agreements are found. The comparison of onset wind speed for flutter between present study and full aeroelasticbridge model wind tunnel test is satisfactory. In order to evaluate the effect of original angle of attack on flutter characteristics, numerical simulations are also carried out to compute the flutter derivatives of the Humen Bridge girder cross-section in original angle of attack +3° and -3°, it is noted that positive original angle of attack take negative effect on flutter stability of Humen Bridge, also, the correctness of the trend line of A'2 in original angle of attack +3? which was obtained from section model tests by using the FVT, is validated.5) The FVM code is used to compute the flutter derivatives and critical wind speeds of the Great Belt East Bridge in Denmark. It is shown that the flutter derivatives of the Great Belt East Bridge are closed to results from section model wind tunnel tests, and the computed onset wind speed for flutter obtained from simulations is little higher than that from wind tunnel tests, and reasonable explanations are presented.6) The aerodynamic devices used to improve bridge flutter stability under smooth flow are discussed by means of numerical methods. The flutter derivatives, including those of the ideal flat plate with different slot ratio in center and different shape of fairing attached to box girder section, are computed. It is shown that a slot in center is effective to increase the onset wind speeds for flutter, and the onset wind speeds for flutter increase with the width of slot. It also indicates that different shape of fairing has different effect on flutter stability of bridge girder cross-section, the effective shapes for individual girder cross-sections can be determined by the flow properties around the cross-section, that is, the both side angle of the fairing should be almost the same as t...