用于索承结构中斜拉索开环振动控制的磁流变阻尼器设计

斜拉索被广泛应用于索承结构,如大跨度桥梁或屋盖结构等.由于极低的内在阻尼,斜拉索易发生因其支承的运动或天气状况影响而引起的大幅值的振动.这些振动可以危及斜拉索本身以及整个索承结构的安全与寿命,甚至引起人们对该类结构信心的降低.在斜拉索减振的诸多方法中,采用磁流变阻尼器的智能阻尼技术近来引起了人们的研究兴趣.该阻尼器的阻尼特性可以通过调节(控制)磁场的输入电流/电压而改变,从而实现在不同振动(频率及幅值)情况下的最优或次优减振效果.本文发展了一个数学模型用于评价在开环控制状态下斜拉索-阻尼器系统的阻尼比.该模型考虑了阻尼器的安装高度、阻尼系数、刚度、质量、支撑刚度、磁变阻尼力以及斜拉索的垂度与倾角等因素,推导出了一个‘广义的通用公式’用于阻尼器参数的设计与优化,即寻求可提供系统最大阻尼比的最佳阻尼器参数.本文以目前世界最长斜拉桥——苏通大桥的最长斜拉索为例,确定了能够提供足够的阻尼以抑制风雨振的阻尼器安装高度以及相应的阻尼器参数.

Design of MR dampers for open-loop vibration control of stay cables on cable supported structures

Stay cables are widely used in cable supported bridges and roofs. Due to extremely low inherent damping, cables are prone to vibrations with overdue amplitudes induced by support motions and by weather conditions. Such vibrations may cause reduced life of the cables and the whole structures, and the risk of losing public confidence in cable supported structures. Among kinds of countermeasures for mitigating cable vibrations, smart damping technology using Magneto-Rheological (MR) dampers attract recent research interest. The damping property of MR dampers can be controllable by tuning the current/voltage inputs for achieving the optimal or sub-optimal damping performance under various vibration conditions (frequencies and amplitudes). This paper presents a mathematical model for evaluating the damping ratio of the cable-damper system in the open-loop control mode, which takes into account the damper installation height, damper coefficient, damper stiffness, damper mass, stiffness of the damper support, and magneto-dependent force of the damper, as well as the sag and inclination of the cables. A 'generalized universal formula' is derived and a 'generalized universal curve' is plotted for damper design and optimization. The design value for damping enhancement is introduced by multiplying the minimum value of damping ratio required for suppressing rain-wind-induced cable vibration with a safety factor. Taking as an example the longest cable on the word's longest cable-stayed bridge-Sutong Bridge, China, this paper achieves to determine the installation height of the damper and the corresponding optimal damper coefficients for providing enough damping to suppress the rain-wind-induced vibration.