Numerical Simulation And Field Measurement Study On Wind Characteristics At Bridge Site In Mountian Valley

With the continuous development of national economy and the advances in science and technology,in order to meet the needs of transportation construction in the mountain areas of southwest China,long-span bridges that cross deep canyons continue to emerge.The longspan bridges is generally flexible,which makes them extremely sensitive to wind effect.Therefore,wind-resistant design of the long-span bridges has become a necessary task.The investigation on wind field characteristics at bridge site is the prerequisite for wind-resistant design of the long-span bridge,and the wind environment of mountain valley in southwest China is very complicated.It is still superficial to understand and study it,which seriously affects the accuracy and safety of wind-resistant design of the long-span bridge.In this paper,the wind field characteristics at bridge site in mountain valley of southwest China is comprehensively studied based on CFD numerical simulation and field measurement methods,as well as necessary theoretical analysis and wind data from meterological station.The major contents and conclusions are summarized as follows:Aiming at boundary transition of terrain model for wind field characteristics measurement,the continuity principle applying for the boundary transition of the terrain model is proposed.Meanwhile,depending on this principle,a kind of transitional curve based on the hyperbolic tangent function is also proposed.The results indicate that this proposed transitional curve can transition incoming flow well,and when distance from the transition region is far,the influence of transition section is negligible.Then,a novel numerical simulation method is proposed based on the Open FOAM to obtain the wind field characteristics in mountain valley.To achieve high-quality numerical simulation,a new calculation domain with boundary transition is adopted,and the inflow condition is dealt with the “virtual weather station” method.Field measurement activities based on wind speed measuring equipment,such as Windcube Lidar and wind mast(with ultrasonic anemometer and cup anemometer installed),are carried out at bridge sites in mountain valleys of southwest China.The mean and fluctuating wind characteristics at the bridge sites are studied in detail depending on the measured wind speed data,and the general laws of them are summarized.Meanwhile,they are compared with the relevant specification,so as to understand their similarities and differences with recommended values.The measured results show that the air flow along the canyon at high wind speed,and mean wind profile is not in agreement with the specification,such as the fitting index tends to be small value;the daily maximum wind speed follows Weibull distribution very well.In addition,the turbulence intensity,turbulence integral scale and gust factor all agree with lognormal distribution,and the measured wind spectra conform to von Kármán spectrum;the turbulence intensity and gust factor decrease with increase of wind speed,but the turbulence integral scale go up;each component of the turbulence intensity at high wind speed are approximate 0.1,0.07 and 0.07,with a ratio of 1:0.70:0.70.Then,the wind field characteristics obtained from two wind masts at different locations(i.e.bottom of valley and hillside)in a mountain valley are compared and analyzed.The results indicate that mean wind speed,wind direction,turbulence intensity,gust factor and wind power spectra at different locations within a certain height range in mountain valley are almost the same,and the difference can be negligible.For a bridge to be built in a mountain valley,based on the wind data from meterological station near the bridge and field measurement,the correlation of daily maximum wind speed between the bridge site and the meteorological station is analyzed,and the basic wind speed of the bridge site is calculated depending on estimated basic wind speed of the meteorological station.Then,the design wind speed of the bridge is estimated based on CFD numerical simulation results.Finally,the fluctuating wind characteristics(such as turbulence intensity,turbulence integral scale and wind spectra)of the bridge girder is analyzed,according to field measurement results and their general laws.