Study Research On Wind Characteristics At Bridge Sites With Multiple Mountains Under Local Wind Environment

The mountainous terrain is complex and changeable,with vertical and horizontal ravines,surrounded by mountains,resulting in irregular distribution of local mountain wind environment.Existing special studies mainly focus on the wind characteristics of mountain canyons,and there are few systematic analysis of local wind environment changes under the action of multiple mountains.For bridge structures surrounded by mountains,most of them are specific studies on specific projects,or the wind speed is corrected with the help of experience,and there are no specific provisions for the value of wind resistance design parameters.In order to accurately analyze the wind field structure of bridges in mountainous areas,the characteristics of the wind field at the bridge site must be clarified.This paper takes the mountainous terrain of Xishang Expressway as the research object,and studies the change law of the wind field at the bridge site with multiple mountains and the change law of the acceleration ratio of the bridge position induced by the main terrain parameters.In this regard,this paper takes numerical simulation as the main research method,uses ANSYS FLUENT,calls and generates terrain surfaces through 3D digital software,and establishes a series of related mountain models with Gambit and Rhinoceros.The reliability of the numerical simulation is verified by the measured terrain,so as to study the change of wind characteristics at the location of the multi-mountain bridge,and provide a data reference for the wind resistance design of the multi-mountain bridge.(1)For the theoretical analysis of typical mountain models and models based on Reynolds-averaged N-S equations(RANS),the optimal mountain contour equation and turbulence model are selected.Taking the cosine mountain and the Realizable turbulence model as the numerical calculation model for the study of the wind field characteristics of multiple mountains,and taking the double mountain as the research object,the average error ratio is used as the criterion to analyze the distance between the top and the foot of the mountain when the distance between the mountains is 0m and 100 m.Variation of wind characteristics at ground height.(2)Taking the actual engineering as the background,and considering the key factors affecting the wind characteristics such as the terrain surface,the height of the main girder,and the wind speed grade,the simulation analysis of the wind field characteristics under the actual terrain of the bridge location under eight working conditions is carried out,and the multi-mountain bridge location is summarized.The law of the characteristics of the wind field at the site,from the calculation results of the typical bridge wind parameters,the wind angle of attack has a great influence,which basically remains at-20°～20°,which is generally-3°～3°specified in the code,the overall distribution of measuring points 0 to 10 along the main beam direction changes in an "M" shape;through the comparison with the measured data,the reliability of the numerical calculation in this paper is further verified,which lays the foundation for further numerical analysis.(3)Based on the above numerical calculation turbulence model,and further based on the simplified terrain,the influence of the distance,height and slope of the mountains on the change law of the bridge position wind field under the typical arrangement of multiple mountains was further studied.Within 100 m,the influence of the surrounding mountains can be ignored after more than 100m;when the surrounding type is arranged,the formula for the height of the bridge position and the terrain correction coefficient at special positions are given.At this time,the acceleration ratio of the bridge position in the direction of the windward side of the mountain is linear.The terrain parameters are corrected with exponential reduction,the mountain height correction range is 0.447～0.646,and the mountain slope correction range is 0.376～0.735;from the perspective of the average acceleration ratio and the change range of the terrain parameters,the influence of the change of the mountain height on the wind field should be greater than the slope of the mountain.