Wind Field Simulation Of Transmission Tower Line System And Unsteady Analysis Of Wind Induced Galloping Of Transmission Line

As a key component of national power system,transmission tower line system is a lifeline project undertaking power transmission,featuring large flexibility,light weight and low damping.The dynamic response of transmission tower line structure is sensitive to wind load,which is the key environmental factor to be considered in the structural design.The movement mechanism of transmission tower line system under the action of wind is very complex,which is easy to cause large gallop of conductors and destabilization of transmission tower.This will have a great impact and cause serious national economic losses.Therefore,stochastic wind field simulation is the key part in stochastic dynamic analysis and reliability evaluation of complex engineering structures such as transmission tower line system.At present,although interpolation method has been widely used in improving Cholesky decomposition in stationary wind field simulation,there is no research combining interpolation method with dimension reduction method for wind field simulation.Wind loads appearing in practical projects often have non-stationary statistical characteristics and are simulated as non-stationary stochastic processes,especially in extreme wind environments such as tornadoes,typhoons and downburst.More and more attention has been paid to the simulation of non-stationary wind loads.Accurate and efficient numerical simulation of non-stationary process is the precondition for studying the aerodynamic characteristics of structures under non-stationary wind loads.The simulation of non-stationary wind loads can provide an effective method for system input in the study of structural system response under complex wind field environment.Therefore,it has considerable value both in theoretical method and in engineering application.Some researches have found that there is time-varying coherence function in the measured nonstationary wind field.However,at present,the simulation of non-stationary wind field with time-varying coherence function is based on traditional spectral expression method,and the simulation efficiency still needs to be improved.Under the action of wind,rain,snow and other multiple environmental loads,the transmission line often ice on the surface,and the asymmetrical cross-section occurs,and then the galloping occurs.At present,the analysis of conductor galloping is generally based on the quasi-steady theory,but the quasi-steady theory ignores the unsteady effects caused by the vibration history and frequency dependence of the actual flow around,so the applicability and accuracy of the quasi-steady theory need further study.However,in the field of galloping numerical simulation of unsteady transmission line,the current research mainly focuses on the variation of aerodynamic damping,aerodynamic force,vibration amplitude and other parameters on wind speed or wind attack angle,and there is no comparative study on the unsteady numerical simulation and wind tunnel test results.In addition,the existing research on static and dynamic aerodynamics mainly focuses on the difference between static and dynamic aerodynamic coefficients,and does not involve the quasi-steady and dynamic aerodynamic time history comparison.In Chapter 1 of this thesis,the current research status of stationary/nonstationary wind field simulation and iced conductor gallop is summarized,and the deficiencies of the current research and the main work of this thesis are clarified.In Chapter 2 of this thesis,the dimension reduction technique and Hermite interpolation improving Cholesky decomposition are combined to simulate the fluctuating wind field of transmission tower-line system,thus a more efficient simulation method than the current numerical simulation methods of transmission tower-line system is proposed.Structural characteristics and wind field characteristics should be considered in wind field simulation of transmission tower-line system.For the transmission tower,only along and across winds are considered and simplified as two independent one-dimensional wind field.For transmission lines,the fluctuating winds in the cross and vertical wind directions should be considered as correlated two-dimensional wind fields.Based on the above research foundation,Chapter 2 of this thesis carries out one-dimensional and multi-variable fluctuating wind field simulation for transmission tower,and two-dimensional and multi-variable fluctuating wind field simulation for transmission lines.In Chapter 3 of this thesis,a fast simulation method for unsteady fluctuating wind field of transmission tower line system is proposed based on wave number frequency spectrum.Previous studies have found that there is time-varying coherence function in the measured non-stationary wind field,and further found that the calculation results of structure response with and without time-varying coherence function model are quite different.Therefore,it is of great engineering significance to simulate the non-stationary wind field with time-varying coherence function.However,at present,wind field simulation of time-varying coherent function is based on traditional spectral expression,and the simulation efficiency still needs to be improved,especially when the simulation object is multi-variable wind field of large-span structure.Therefore,in Chapter 3,a non-stationary wind field simulation method considering time-varying coherence function based on wave number frequency spectrum is proposed,and space and time variables are separated by proper orthogonal decomposition(POD).This method can avoid time-consuming Cholesky decomposition and significantly reduce the simulation time due to the use of two-dimensional FFT after variable separation.In Chapter 4 of this thesis,taking typical crescent-shaped icing conductor as the research object,the analysis of the unsteady and quasi-steady of icing conductor galloping is carried out.The fourth chapter is divided into two parts:wind tunnel test and numerical simulation.In terms of wind tunnel test,aerodynamic forces in uniform flow field at different angles of attack of ice-coated conductor segment model were measured in a wind tunnel using force balance.The dimensionless variation of aerodynamic coefficient with angle of attack is studied and the instability interval of ice-covered conductor which is easy to gallop is calculated according to Den Hartog theory.Then the conductor aeroelastic model galloping tests under different wind speeds are completed,and the displacement response time histories in vertical,transverse and torsional directions are recorded and the vibration characteristics are analyzed using contactless measurement technology.In terms of numerical simulation,a numerical simulation model which is consistent with the aeroelastic model of ice-coated conductor is established.The CFD fluid-structure interaction unsteady theory method is adopted to analyze the calculation model response.Finally,the measured response of wind tunnel test is compared with the calculated results of unsteady and quasi-steady numerical simulation.Furthermore,the difference between dynamic aerodynamic force and quasi-steady aerodynamic force is compared,and the applicability of numerical simulation results based on unsteady method and quasi steady assumption is verified.The Chapter 5 summarizes the main work and innovation of this thesis,and looks forward to the next research work.