Narrow Results

In this paper the models of the transmission line with one DOF, two DOFs and three DOFs are constructed respectively by using Hamilton principle, where the initial location, the geometric nonlinearity caused by deformation and the aerodynamic nonlinearity caused by flow are considered. These simple models are accurate and can be used for the theoretical analysis. In actual engineering, the critical wind speed of galloping has been paid more and more attention. Therefore, in this paper the critical wind speeds are obtained by Lyapunov stability theory and the effects of structural parameters to the critical wind speed are discussed for different models. And the response curves of the system with one DOF and two DOFs (out-of-plane motion) are obtained by using harmonic balance method and multiple scale method, respectively. The bifurcation of the system moving out-of-plane is analyzed by singularity theory. For the systems whose motion is coupled with torsion, the numerical results are given by using the fourth order Runge–Kutta method. Additionally, the effects of the dynamic vibration absorber and detuning pendulum to the anti-galloping of the transmission line are studied for different cases.

The suppression of oscillations of an elastically mounted prism under galloping by a dynamic vibration absorber (DVA) with linear damping and stiffness is investigated. A model considering the dynamic coupling of the prism and the DVA is constructed, with the aerodynamic loads acting on the system represented by a quasi-steady approximation. Based on the coupled nonlinear governing equations of motion, a linear analysis is first conducted to explore the coupled frequency and damping, and the onset speed of galloping in the presence of the DVA. Subsequently, the normal form of the Hopf bifurcation for the coupled system near the onset of galloping is derived to characterize the type of instability (supercritical or subcritical), while evaluating the effects of the DVA parameters. The results show that with appropriate parametric values, the DVA has great impact on the onset speed of galloping and can significantly alleviate the oscillation amplitude of the prism.

This paper presents evaluations of coupled two-degree-of-freedom (2DOF) galloping oscillations of slender structures with nonlinear effects, involving coupled transverse and rotational motions. The nonlinear governing equations of the coupled motions are derived by developing nonlinear formulations of the quasi-steady aerodynamic forces and damping coefficients. By solving the eigenvalue problem of a perfectly tuned 2DOF system, an analytical expression of the minimal structural damping ratio required to prevent coupled transverse-rotational galloping is established. The influences of various parameters, such as angle of wind attack, structural height, width and aspect ratio, on the onset wind velocity for the occurrence of coupled galloping are then analyzed in detail by numerical simulations. Comparisons of the onset wind velocity of the coupled 2DOF and uncoupled single-degree-of-freedom (1DOF) galloping are presented and discussed. The nonlinear vibration behavior of coupled 2DOF galloping of slender structures under varying wind speeds is also investigated.

Vortex-induced vibrations are often unwanted as they can lead to catastrophic failure of the associated structures, warranting countermeasures to mitigate or suppress these vibrations. Due to the nature of nonlinearities in fluid–structure interaction (FSI) problems, analytical solution techniques for FSI problems have limited applicability at best. On the other hand, the numerical solution of vortex-induced vibrations is quite challenging, especially for problems undergoing large structural deformations, let alone the simulation of effective control techniques for suppressing unwanted vibrations. In this work, a robust and computationally efficient simulation framework is proposed to simulate fluid–structure–control interactions problems involving rigid or flexible structures. The effectiveness of the proposed framework in designing effective controller mechanisms for controlling the onset as well as the amplitude of vortex-induced vibrations is illustrated by studying the examples of lock-in of a circular cylinder, galloping of a square body and vortex-induced vibrations of a flexible, lightweight beam under different parameter settings for the controllers.

Carry out conductor anti-galloping research on Xiangjiang large span in Xiluodu - Zhexi ±800kV ultra-high voltage DC transmission engineering. This paper analyzes metrological and terrain conditions of the area passing by Xiangjiang large span engineering, which clarifies galloping occurrence condition of the conductor in the large span engineering; give out main galloping characteristics of Xiangjiang large span engineering under given meteorological conditions by means of value simulation method.