Investigation On Identification Method Of Galloping Characteristic Parameters And Wind Load Of Transmission Lines

Understanding characteristics of transmission line galloping is the basis to develop galloping control technology.Existed main methods to study the galloping characteristics include theoretical analysis,numerical simulation and experimental observation.There are many investigations on the theory and numerical simulation of galloping.However,due to the uncertainty of ice accreation and wind field,using real test line to study galloping characteristics has become very important means.It is a key problem that how to use the measured data of test line to identify the galloping characteristics.On the other hand,dynamic swing,wind-induced vibration and galloping phenomena of transmission lines may take place in the wind loads,so the determination of the wind loads on transmission lines is a key to understand and solve these problems.Because the wind field acting on the line is distributed random load and the aerodynamic forces during motion are related to the fluid-solid coupling problem,it is very difficult to measure the loads employing ditect means.It is rgent identify the wind load by means of inversion technique.In this paper,firstly,the displacement and wind velocity time histories of the bserved points are given out as two typical galloping events happened in the real test transmission line at Jianshan of Henan province,China.Based on the spectrum analysis of the displacements and wind speed,it is shown that the motion of the conductor in the real wind field may contrain low frequency gust responses besides the self-excited vibrations.Due to difference between the characteristics of self-excited response and those of gust responses,it is necessary to identify the characteristics of the self-excited vibration and gust response,which provides the necessary foundation for the study of the galloping control technology,at the same time.Combined with the random decrement method and the characteristic system realization algorithm(RDM-ERA),the characteristic parameters of the actual galloping events of the real test line are identified.The parameter identification software is written by MATLAB,and the correctness of the software is verified by the vibration experiment.The frequencies,mode components and the net damping of the self-excited response are obtained by means of this method using the displacement time history responses.The analysis of the identified parameters shows that the self-excited vibration of the two events is dominated by vertical vibration.The main vibration frequencies correspond to the lower order of natural frequency.The net damping is negative,which reflects aerodynamic damping.According to the principle of random decrement method,the random decrement functions are a non-forced vibration response signals.However,the RDM-ERA method can be used to identify the modal parameters whether its energy is dominant or weak in the self-excitation response.Because the gust response characteristic parameters can not be identified by menas of the RDM-ERA method,the combined method of the natural excitation technique and the characteristic system realization algorithm(NExT-ERA)is used to identify the characteristic parameters of the actual galloping events.The parameter identification software was developed,and the method and software are verified by means of a beam vibration test.It is shown that the gust response is identified besides the characteristic parameters of self-excited vibration response.However,compared with the RDM-ERA method,the NExT-ERA method may omit the modal parameters of the self-excited response,whose energy is weak.Comparing the principles and identification results of two identification methods,each one has its own merits.It is suggested that the two methods should be used to identify the galloping characteristic parameters simultaneously.Based on the finite element model and the quasi-uniform B spline basis function decomposition,a method to identify distributed dynamic load of one-dimensional structure in time domain is presented.The load identification software was developed with MATLAB.In order to verify the method and software,the load identification of the simply supported beam subjected to the distributed dynamic load and the influence of noise on the identification of distributed dynamic load are studied by means of numerical simulation.A new method to identify distributed dynamic load with space and time division is proposed based on the concept of piecewise clamped B spline surface.By means of this method,the load distribution can be more accurately identified due to structural space division and longer time history of the load can be identified due to time division.Time history of the random wind load acting on a transmission line is identified by means of this method,and the influences of division number and noise on the identification accuracy are investigated by means of numerical simulation.It is shown that the proposed method can effectively identify the distributed random dynamic loads on a transmission line.