Study On The Complex Wind Field Characteristics Of Mountainous City Bridge Site

In the 13 th Five-Year Plan,deep implementation of the western development strategy was given priority,the construction of the long span bridges is necessary.The research of the wind field characteristics at the bridge site is a hot issue on bridge's wind resistance,the research of the complex wind field characteristics in mountainous cities are oppositely less.Using normalization blindly may cause a wide deviation with actual result,with rapid development of CFD and the production of wind tunnel test,it takes good news for scholars who study areas lacking meteorological data.Chong-qing,Chao-Tian-Men bridge contains characteristics of complex mountainous cities,the paper covers the following areas:(1)Combined with the history of bridge's wind engineering,the effect of wind on the structure was produced,and the wind field characteristics of Chong-qing,Chao-Tian-Men bridge were studied.Two methods of bridge wind resistance measure and fluctuating wind simulation were briefly introduced in this paper.(2)There are four basic equations of fluid mechanics in this paper:continuous equation,equation of motion,Navier-Stokes equations,energy conservation equation.This paper has described the advantages and disadvantages of the four kinds of solutions to the Navier-Stokes equations.In addition,the formation mechanism and characteristics of complex boundary layer were also introduced.Four criteria for the principle of wind tunnel experiment are geometric similarity,kinematic bunching similarity,dynamic similarity,similarity of boundary conditions.(3)Elevation data of complex mountain were gotten by using Google Earth,after coordinate conversion the data were imported in Gambit and then terrain surface of complex mountain was produced directly.The suitable UDF wind profile was selected by combining the wind-resistance standard of Japan and China,turbulent models were contrasted,non-equilibrium wall function and RNS turbulent model were selected to simulate the complex motion characteristics of fluids on near-ground.A wind tunnel test for a model of mountainous land form around Chong-qing,Chao-Tian-Men bridge,every 20 m from main beam to vault the wind speed was tested,numerical simulation and theoretical calculation were compare with the data of wind tunnel test.Conclusions are as follows:Using Google Earth to help Gambit establish the model of complex mountainous land form exhibits high reliability;The numerical simulation ofcomplex wind field characteristics in mountainous cities has a high precision.(4)Turbulent wind was extracted by classification of time history curve of speed of following wind,expression turbulent wind spectrum was list,in theoretical terms wave superposition method and the process of simulation fluctuating wind speed by AR analogue method were introduced.Based on that,Davenport wind velocity spectrum was selected,every 20 m from main beam to vault,the wind speed of Chong-qing,Chao-Tian-Men bridge was synthesized through harmonic method and AR method.The results show that:Fluctuating wind spectrum simulated by AR method was relatively stabler,and the object power spectrum was more close.