Numerical Simulation Research Of Wind Effects On Bridges

Due to the improvement of the computational fluid dynamics (CFD) theory andthe development of computer technology, the CFD is rapidly maturing. Although itcan’t fully replace wind tunnel test， there are several advantages compared withtraditional wind tunnel tests, such as short test period, low cost and detailed flowvisualization, etc. As a result, the CFD becomes an effective tool to study the windeffects on bridges. In this paper, the CFD was adopted to investigate the wind effectson bridges.(1)The two equation turbulence model of standard SST k-was adopted tosimulate the aerodynamic coefficients of Lishui Bridge under different wind attackangles, and then the simulation results were compared with those from wind tunneltests. Furthermore, the wind pressure and velocity distributions around the main beamcross-section were presented and discussed. It is found that CFD is effective tosimulate the aerodynamic coefficients and display wind flow fields.(2)The two-dimensional Reynolds-averaged Navier-Stokes (RANS) codeequipped with SST k-turbulence model was applied to solve N-S equations ofincompressible viscous fluid using FLUENT software. A rectangular cylinder wassimplified to two-dimensional mass-spring-damper system. The initial mesh schemewas built by adopting the domain decomposition method (rigid moving zone plusdynamic zone plus stationary zone). And the equation of structural vibration wassolved by the dynamic mesh and embedding the code of Newmark-method inFLUENT with user defined functions (UDFs). In this way, the numerical simulationmethod for the vortex-induced vibration (VIV) of a bluff structure was established.After that, this method was applied to simulate flow and vortex-induced vibration ofrectangular cylinder with aspect ratio of6, for various cases with different windvelocities. The results showed that the lock-in region and VIV amplitudes of therectangular cylinder were in good agreement with the wind tunnel experimentalresults. The method presented in this study is feasible to conduct the numericalsimulation of VIV of bluff section together with separation and reattachmentphenomenon.(3)The phenomenon of wind-driven rain (WDR) on the rectangular cylinderwas investigated based on the Euler-Euler two-phase flow theory, in which the rain was regarded as continuum, and UDF programs were compiled in the FLUENTsoftware. The catch ratio and rain-induced impact loads on the walls of the model, anddifferent rain flow patterns of different raindrops size and velocity were obtained bythe RANS method. Meanwhile, the load time-histories and force spectra inalong-wind, across-wind and torsional directions were obtained by Large eddysimulation (LES) method. It is found that the static loads influenced by WDR aresmall, but for dynamic loads, such effect becomes larger, from the comparisonbetween the cases with rain and without rain. On the other hand, the average effect ofrain is small.Comparing with wind tunnel test, it is effective to investigate the wind effects onbridges by means of the CFD methods adopted or proposed in this paper, in particularfor cases without wind tunnel facilities. In addition, the numerical methods also havethe advantages of little cost, shorter duration, and repeatability. In a word, the CFD isan effective method for choosing aerodynamic shape and identifying aerodynamicparameters for analysis and design of bridge structures.