Study Of Nonlinear Effects And Entire-Process Failure Of Transmission Lines Under Strong Monsoon And Tornado

The investigations of wind resistance and wind design of transmission lines mainly focus on the synoptic climate which is large scale meteorological wind,rarely involved in extreme climate such as tornadoes,and the failure mechanism of the transmission lines under strong winds is not well understood.Due to the significant differences of wind characteristics between synoptic wind and tornado,the wind load parameters in current design code may no longer applicable for the design of transmission lines under tornado.However,the number of the ultra-high voltage(UHV)transmission lines growth rapidly,and the extreme climates such as tornadoes occurs frequenly in recent year.Hence,it is urgent to conduct the researches on the wind loading and wind effect of transmission lines under the strong wind and tornado.Aopting the self-supporting transmission tower system commonly used in UHV transmission lines as the research object,the wind resistance of the transmission lines under strong monsoon and tornado is studied by using theoretical analysis,wind tunnel test and vecotor form intrinsic finite element method.The tornado load characteristics,wind load calculation method of transmission lines,the application of vector form intrinsic finite element(VFIFE)method on transmission lines,the wind-induced non-linear effect and entire-prcocess analysis of wind-incued failure have been conducted.The main research contents are as follows.(1)Research on tornado load characteristics of transmission towers: Using the tornado vortex simulator(TVS)in Tongji University,physical simulations of stationary tornadoes with different aspect ratios,radial Reynolds numbers and swirl ratios were carried out to study the wind field structure and three-dimensional wind distribution of the tornado field and to explore the influence mechanism of control parameters on the tornado structure.Based on the force measurement tests of rigid model of transmission tower,the overall aerodynamic coefficients of the tower which is placed in stationary tornado were conducted,and the influence of swirl ratio on the tornado load of the tower was explored.The force measurement tests of the tower model which is placed in translating tornado were also carried out,the effect of translating speed,path and yaw angle on the tornado load of the tower were studied.(2)Research on wind load calculation method of transmission lines: The conventional model of strong monsoon and the three-dimensional analytical model of tornado were sorted out.The comparison study of different analytical model based on experiment data was conducted.Two methods for calculating wind loads on lattice transmission tower--the global approach and the local approach,were discussed.And on this basis,the wind load analysis method of transmission tower applicable to the tornado analytical model was proposed.(3)Research on vector form instrinsic finite element method for failure analysis of transmission lines: The basic concept of vector form instrinsic finite element method was introduced,the three-dimensional nonlinear beam element applicable to frame structures such as transmission towers was propsed,and a vector form intrinsic finite element analysis platform was developed and verified.(4)The wind-induced non-linear effects and entire-process analysis of the transmission lines under strong wind: Based on the VFIFE analysis platform developed in this paper,the VFIFE model of transmission lines was established,and the windinduced response of the transmission lines under strong monsoon was carried out.The vibration characteristics of the transmission lines were studied,the effects of wind speed and yaw angle on the response of the tower lines and the capacity of the tower lines to strong monsoon are explored.On this basis,the entire-process failure analysis of tower lines under strong monsoon was carried out,and the failure process and failure mode of tower lines were discussed.(5)The wind-induced non-linear effects and entire-process analysis of the transmission lines under tornado: Based on the VFIFE model of transmission lines,the non-linear static push over analysis of the transmission lines under stationary tornado was conducted,and the effects of vortex radius,radial distance and yaw angle on the capcity of the transmission lines to stationary tornado were studied.The nonlinear dynamic response of the transmission lines under translating tornado was also carried out,and the effects of tornado path and translating speed on the response of the transmission lines were explored.On this basis,the entire-process failure analysis of tower lines translating tornado was carried out,and the failure process and failure mode of tower lines were discussed.