Analysis Of Large-span Transmission Line Vortex-induced Vibration

With the large-scale construction of high-voltage transmission lines in China, the wind vibration is prone to occur due to the increasing of the line diameter, the gravity per length and the suspended height. Its destruction will cause tremendous economic loss and other secondary disasters since high-voltage transmission project is an extremely important lifeline for the society. This paper is a preliminary research of the transmission line VIV, and the specific contents are as follows: the improvement of energy balance method, the solution of VIV on the basis of analytical model through utilizing Dynamics, based on three-node cable element model and based on transmission line VIV model by taking the consideration of bending stiffness analysis, the details are as follows:Firstly, the defects of calculating VIV is analyzed in the paper by the traditional energy balance method and the discussion is extended from wind input power, power transmission line from the damping, environmental conditions, wind speed and wind direction etc. The improvement of the wind power input lies in the introduction of uniform wind turbulence reduction factor, and the reduction of wind input power, so that it can consider the impact under different site conditions; the analysis is based on three self-damping models of transmission lines, which makes transmission line self-damping can consider the influence of the materials, span, average operation tension, the suspended height of transmission line.The solution of VIV is on the basis of analytical model through utilizing Dynamics. To improve the efficiency, this paper utilizes the D'Alembert principle to establish a balanced transmission line equation of motion, and uses separation of variables to build transmission lines for the variable nonlinear vibration function Campaign balance equation, without considering the inherent vortex-induced and structural coupling between the modes. The equation is solved by the software MATHEMATIC. Analyses indicate that the low-frequency components of the transmission lines VIV amplitude is larger than high frequency components amplitudes, and the amplitude of SDOF for the finite element model is smaller than that of energy balance method.A three-node cable element model is established, The analysis of vortex strength parameters is carried out through the application of nonlinear model Scanlan expression of the proposed empirical vortex strength, Single degree of freedom system being equivalent to a power transmission line from the damping mode from the damping coefficient, the finite element method and the motion equation of the formation of assumed VIV with bands are introduced. The solution of the equation is based on modal decomposition and finite differential method. Analyses show that with the increase of wind speed, the steady-state response of the VIV resonance region by three-node cable element model is a little smaller than that by the energy method. As the wind speeds up, the steady-state response of the gap increases. When the wind speed is 2m/s, the gap is 12.65%, when the wind speed increases to 5m/s, the gap becomes 33.76%.Transmission line VIV model in the consideration of the influence of bending stiffness analysis is established. To consider the influence of flexural rigidity on the transmission line wind vibration, the displacement vector of curved beam element with the fixed coordinate system is established through polynomial interpolation function on the basis of curved beam theory; all units of mass and stiffness matrix are obtained through the principle of virtual work, With the mass, stiffness matrix in the moving coordinate system being converted into the global coordinate system mass, stiffness matrix, the VIV kinetic equation is worked out by using a single degree of freedom system power transmission line from the equivalent modal damping from the damping coefficient. The motional equation is solved though applying Modal decomposition and NEWMARK method. Analyses show that the steady-state amplitude of transmission line VIV model in the consideration of bending stiffness is larger than that in the non-consideration of bending stiffness, and the error is smaller at low wind speed, but at high wind speed, the error is up to 39.49%, which can not be ignored.