Energy Based Dynamic Stability Analysis Of Transmission Tower-line System Under Downburst

Downburst,as a disastrous strong downdraft near the ground,is obviously different from boundary wind in velocity distribution and structural failure characteristics.Wind load is often the main load for transmission tower design.However,boundary layer wind profile is still used to determine the design wind load of transmission tower in many countries.This may lead to unreasonable tower design.Many researchers have recently recognized the importance of downburst resistance and conducted failure analysis on the design of transmission towers,Meanwhile,the collapse mechanism of transmission tower under the action of downburst is still to be fully understood.The dynamic stability of truss structures is an important problem in engineering field.So far,many dynamic stability criteria have been proposed for different systems under various loads.It is an intuitive and effective method to identify dynamic instability by analyzing the energy time history responses of nonlinear dynamic systems under arbitrary loads.Taking the transmission tower line system under the action of downburst as an example,this paper studies the dynamic stability and collapse mechanism of the transmission tower line system under the action of downburst from the perspective of the energy change of the power system,Based on the above problems,the research work of this paper mainly includes the following aspects:(1)Based on the time-varying average wind speed simulation method of the improved OBV(Oseguera&Bowle/Vicroy)model,the time-varying average wind speed of the downburst is combined with the pulsating wind speed obtained by the harmonic superposition method.Finally,the time history curve of downburst wind speed at the corresponding position of transmission tower and conductor is obtained.Based on the relationship between wind pressure and wind speed,the downburst load is obtained.(2)The "one tower and two lines" transmission tower line system model is established by using ABAQUS software,in which the beam element B31 OS unit is selected to simulate the transmission tower Angle steel member which can better adapt to the warping member.The dynamic elastoplastic analysis of the model is carried out.By studying the internal force and spatial distribution of the plastic strain changing bar(AY bar for short)in the results,the response failure and collapse mechanism of the transmission tower under the impact of the downburst force is determined,and the results are compared with the results of the corresponding static elastic-plastic analysis.(3)Based on the relationship between the characteristic energy and the input energy,the dynamic stability discrimination method based on the characteristic energy was applied in ABAQUS.And the failure time of the transmission tower under the action of the downburst is determined by using the discriminant method of the characteristic energy dynamic stability.