Field Study On The Boundary-layer Characteristics Of Strong/Typhoon Wind Via Lidar Profiler

With the rapid development of flexible civil engineering structures such as high-rise buildings,long-span roofs and Bridges,wind-induced problems have become increasingly prominent in the process of wind-resistant design and their operation and maintenance.Wind field information is the basis for structural wind resistance research.Although people have conducted extensive observation of good winds and established a relatively perfect theoretical system,the field study of exotic winds such as typhoon and downburst is still insufficient,which is highlighted in the aspects of low efficiency of conventional equipment to capture exotic winds and limited observation range.In recent years,Lidar profiler have attracted much attention in the field of wind field measurement due to its easy and flexible arrangement,wide measurement range,and high sampling frequency,and have shown broad application prospects.However,systematic research work on the wind field of strong/typhoon boundary layer based on these devices is still limited.This paper firstly investigates the remote sensing performance of mean and turbulent wind field detected by Lidar profiler and proposes a turbulent wind correction method based on wind spectrum.Then,measured typhoon and downburst through flexible arrangement.Finally,based on the long-term measured data of Lidar profiler,the characteristics of boundary layer wind fields under several typical inflow terrains are summarized and analyzed.The results are compared with the relevant specifications in order to obtain more results conducive to the practice of wind resistance.First,the reliability of Lidar profiler remote sensing data is explored based on two sets of parallel tests with Wind Mast PBL boundary layer type Lidar profiler and two wind measurement towers.The results show that it has high accuracy in remote sensing detection,but the recorded turbulence values are overestimated.The reliability of Galion Lidar profiler remote sensing data was also explored.The results show that it also has high accuracy in terms of remote sensing detection,but the recorded wind turbulence is underestimated,so a qualitative correction is made to fit the wind turbulence.Aiming at the deviation of wind turbulence measured by Wind Mast PBL boundary layer Lidar profiler,a turbulent wind correction method based on wind spectrum was proposed to correct typical wind turbulence measured values.Secondly,the wind field information of two typhoons and five downburst events captured by Wind Mast PBL boundary layer Lidar profiler is analyzed.The results show that（1）for the characteristics of typhoon wind field,the wind parameters obtained by fitting the mean wind profile are different in different incoming flows.The turbulence parameters obtained based on the correction method are significantly different from those before the correction,but the corrected results are more consistent with the results of existing studies,which reflects the necessity and effectiveness of the correction.（2）Downburst events are accompanied by but not limited to sudden changes in wind speed,wind direction,temperature,humidity and signal-to-noise ratio.The mean and turbulet wind fields obtained by classical and directional decomposition methods are very similar.The wind profile has a certain time variation and is different from the common wind empirical model and the recommended profile.Finally,the characteristics of the boundary layer wind field under different incoming landforms are discussed based on the long-term empirical data of the Lidar profiler for offshore,coastal,urban and suburban landforms.The mean wind profile characteristics show that（1）the measured exponentαand roughness z₀ of offshore landforms are smaller than the recommended values of China’s code for Class-A.（2）There is a significant difference between the measuredαand z₀ of coastal landforms under onshore and offshore wind conditions,and the measuredαand z₀ under offshore wind conditions are closer to the recommended values of China’s code for Class-B.（3）There is a significant difference betweenαand z₀of urban landforms and suburban landforms measured in different streams,which are even 7～10times larger than the recommended values of China’s code for Class-D.The corrected turbulence characteristics show that（1）the changes of turbulence along the height are unstable due to the complex and heterogeneous topography.The turbulivity profiles of different incoming flows in the same landform are different from those recommended by some wind load codes.（2）For offshore geomorphic features,turbulence parameters gradually decrease at low wind speed and decrease with the increase of mean wind speed.As the wind intensifies,the effect of ocean roughness gradually becomes dominant.When the wind speed increases further and exceeds the threshold value,the changes of turbulence parameters tend to be stable.The research results of this paper are helpful to promote the observation of strong/typhoon wind field characteristics,especially turbulent wind field characteristics of Lidar profiler,and have certain reference significance for wind resistance design and disaster prevention and reduction of civil engineering structures.