The Study On Application Of Preconditioning Compressible Flow Algorithm In Bridge Wind Engineering

This dissertation reviewed the researches of wind effects on the long span bridge, and summarized the current researches on the numeric simulation in bridge wind engineering. Based on the solving algorithm of unsteady compressible N-S equations considering a preconditioning processing technic, the finite volume method for solving the unsteady low velocity flow field had been established. Using Delaunay triangulation mesh algorithm, the generation of dynamic mesh during unsteady flow field had been achieved. Developed professional software can be used for effective numerical calculation of aerodynamic parameters and numerical simulating of aerodynamic phenomena of bridge girders. The static aerodynamic force coefficients and flutter derivatives can be obtained, and the phenomenon of vortex-induced vibration can be simulated using the software.The dissertation mainly contains following contents:1. By using a preconditioning processing technic expanded into the unsteady compressible N-S equations, the problems of the algorithm tending to fare poorly for low speed flow fields can be solved.2. Using Delaunay triangulation mesh to locate the relationship between grid points, the generation of dynamic mesh during unsteady flow field calculation had been achieved. Comparing with the traditional spring mesh method, Delaunay triangulation mesh method need any iterative computation and can provide high efficiency and good stability.3. Developed professional software for effective numerical calculation and simulation of unsteady low velocity flow fields with moving boundaries. The results of several examples indicated that the preconditioning processing technic can extend the effective calculating range of the compressible algorithm to the low Mach number, especially to the low flow velocity condition of wind engineering for bridges. By combining with the structural dynamic equations, the software can provide the simulation of fluid-bridge coupling interaction.4. The static aerodynamic forces of bridge girders were treated with unsteady numerical simulation using the software. The results had a good agreement with the ones in wind tunnel tests. Based on the bluff body bridge girder section and different turbulence models, the solving precision of the static aerodynamic forces had been studied.5. Based on the numerical simulation for the vortex-induced vibration phenomenon in bridges and the analysis of the numerical flow field, a mechanism of vortex-induced vibration is eventually formed:when the vortex-induced vibration occurs, the bridge girder motion induced by initial vortex-induced aerodynamic loads can magnify the following aerodynamic loads, and the amplitude of bridge girder is increasing until the "lock in" status.6. Based on the least squares fitting and the aerodynamic force in vertical and torsion motion, the flutter derivatives of thin plate and bridge girder had been obtained using forced vibration method of numerical simulation. The comparison between calculated results and theoretical results and wind tunnel test results can validate the feasibility of the software in the calculation of flutter derivatives.