Numerical Simulation And Vulnerability Analysis Of Transmission Tower Under Downburst

The transmission network has an important impact on our country’s economic development and people’s lives.Statistics show that the wind-induced damage to most transmission tower structures is caused by downbursts.The downburst is a short-term strong wind caused by the downflow of thunderstorms impacting the ground,and its wind field characteristics are different from the common good wind near-ground wind field.The domestic transmission tower structural design specifications do not provide for the downburst wind load.To improve the safety performance of the transmission tower structure,it is necessary to explore the unique wind field characteristics of the downburst and simulate the failure state of the transmission tower structure in the wind field.The research results can provide reference for engineering design.In this paper,based on numerical simulation,the structural response and wind disaster vulnerability of the transmission tower line system in the downburst wind field are studied.The main contents include: a reasonable three-dimensional downburst wind field is simulated,the distribution of horizontal wind speed in the wind field is explored;an accurate 220 kV actual transmission tower model is established and the failure mode of the transmission tower line structure in downburst and normal wind field are studied;considering the effect of structural randomness,the fragility curve of the transmission tower line structure under different working conditions is obtained.A three-dimensional downburst wind field model is simulated based on Fluent,and the RSM turbulence model and the SST k-ω turbulence model are compared.The empirical models and measured data in the literature verify the rationality of the simulation based on the RSM turbulence model,and the distribution of horizontal wind speed in the wind field is obtained.The transmission tower line coupling model and equivalent tower-line model are established based on ANSYS.The pulsating wind speed spectrum was synthesized by harmonic synthesis method.The equivalent tower line model and the three tower four-wire model under the action of 0° and 90° wind direction angle were subjected to static analysis and dynamic time history analysis.The improved wind vibration coefficient value of transmission tower,transmission line and insulator string are obtained under 90° wind direction angle.The initial failure of the component and the overall failure of the structure are defined as the slight and complete failure of the structure.Based on the material nonlinear theory,the failure status of the equivalent tower line model under different wind direction angles in the downburst wind field and the normal wind field is studied using the pushover method.Based on Monte Carlo simulation,the fragility curve of the transmission tower structure under the downburst wind load is obtained.Due to the lack of statistical data,this paper does not consider the uncertainty of the load but the uncertainty of the structural resistance.Sensitivity analysis was used to determine the structural parameters that have a greater impact on the bearing capacity of the structure.The difference between the effect of the downburst wind load and the normal wind load was discussed,as well as the similarities and differences of the transmission tower response at different locations in the wind field.