| With the increasing development of China’s economy and the construction of new infrastructure,the scale of power grid continues to expand.With the construction and operation of UHV transmission lines,China’s power grid has become the most complex and largest power grid in the world.Transmission tower line system has become one of the important lifelines related to national economic development and people’s living quality.For a long time,tower-line systems are often damaged in bad weather.Data at home and abroad shows that about 90% of the collapse accidents of transmission tower-line systems are caused by strong winds.Among them,downburst,which is often accompanied by near-surface strong winds in extreme thunderstorm weather,causes transmission tower collapse most frequently,and transmission tower line damage caused by this kind of thunderstorm with strong wind occurs from time to time in our country.However,the actual design code of transmission tower line in China does not take into account the downburst with strong wind,it is necessary to study the impact of downburst on the overhead transmission line system.Under such background,based on the simulation of wind field and wind load time history,the dynamic response of transmission tower line system under mobile downburst is studied and compared with the quasi-static analysis according to the method in code.It provides a reference for the tower-line system to resist downburst flow wind.The main research work and conclusions of this paper are as follows:（1）The scale model is established based on the impinging jet model,and the wind field of downburst is simulated by Fluent software.And the independence of grid size,scale ratio and inlet velocity is verified,which shows the feasibility of using CFD method to simulate downburst wind field.Based on the simulated wind field,Vicroy function model is selected as the vertical wind profile of the average horizontal wind speed of downburst.（2）According to the design drawings,the three-tower and two-line model of the double-loop linear angle steel tower is established,and the modal analysis of the tower,line and tower line system is carried out to verify the effectiveness of the model.At the same time,the dynamic characteristics of the structure,such as natural frequency and mode shape are obtained,and the change of dynamic characteristics of transmission tower caused by the coupling between tower and line system is analyzed.（3）Four kinds of downburst wind profiles and conventional design wind speed are selected,and the quasi-static wind-induced response analysis under four wind angles is carried out according to the method in code.The results show that the most unfavorable wind direction angle is 45°.The main material with the weak position of the transmission tower is above the first diaphragm under the downburst flow.（4）The wind speed sampling point is determined.Based on the characteristics of the conventional boundary layer wind,the Davenport spectrum is selected to simulate the wind speed time history of each point.Considering the average wind’s time-varying characteristics caused by the moving effect of the storm and the intensity evolution,the normalized Kaimal spectrum combined with the amplitude modulation function is selected to simulate the wind speed time history of the downburst at each sampling point by harmonic superposition method.（5）The dynamic responses under the conventional design wind speed and the downburst wind acting on the tower line system along different angles are analyzed.There is a coupling effect between the tower lines,and the most unfavorable wind angle is 90°.Under the downburst wind,the coupling effect between the tower lines increases with the increase of the angle between the moving path of the thunderstorm center and the direction of the line.Compared with the results obtained by quasi-static force,this paper illustrates the deficiency of considering downburst for transmission line design directly according to the standard method,and provides some suggestions for this. |
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