流线闭口箱梁断面涡振过程分布气动力演变特性

Evolutionary charateristics of surface pressure around the streamlined closed-box girder during vortex-induced vibration

涡激振动是大跨度桥梁在低风速下较常见的风致振动现象,探究涡振机理是桥梁涡激振动效应评价与控制的重要前提.为深入研究涡振机理,立足于涡振发展的完整过程分布气动力与结构行为同步演变特性分析,深入揭示了分布气动力及其结构行为作用机制.以典型大跨度桥梁闭口流线型箱梁断面为对象,实现了弹性悬挂节段模型同步测力、测振和测压风洞试验.针对典型涡振过程风速关键结点,对比研究了涡振发生前、锁定区上升区、振幅极值点、下降区以及涡振后等不同时期箱梁表面分布气动力演变特性.研究表明,涡振过程箱梁分布气动力特性具有明显的变迁历程,集中体现在涡振锁定区内外表面气动力特性具有显著差异,压力系数根方差、振动卓越频率处压力系数等统计参数与涡振振幅高度相关,气动力与涡振振幅具有明显同步演化关系,尤其是上表面下游、下表面与下游风嘴转角附近区域气动力演变特性显著,是引起涡振的主要原因.该研究为涡振机理研究提供了一种新的思路和方法,未来可应用于其他类型主梁断面.

The vortex-induced vibration （ VIV） is a typical phenomenon of wind-induced vibration in low wind velocities, especially for the long-span bridges, and an important prerequisite for the evaluation and control of the vibration effects on bridges. Based on synchronously evolutionary characteristics analysis of distributed aerodynamic forces and structural effects during VIV, characteristic of distributed aerodynamic forces and their effects on structural behaviors were conducted to reveal the mechanism of VIV. Aiming at a traditional streamlined closed-box girder of long-span bridges, wind tunnel tests of synchronal measurement of force and displacement responses of spring-suspended sectional model were conducted. Pressure-measured tests were implemented to investigate the spatial aerodynamic distribution of the girder during VIV. Surface pressure distributions in different amplitude-developing period during VIV were compared, including pre-VIV period, ascent stage, amplitude extreme point, descent stage and post-VIV period. It is found that aerodynamic characteristics of the model has obvious changes during VIV, indicating that there are obvious differences between lock-in period and non-VIV period. The distributed aerodynamic forces and the amplitudes of aerodynamic forces at predominant frequency are positively correlated with the amplitude of VIV responses. The aerodynamic characteristics and the VIV response during VIV are synergistic, especially nearby downstream region of upper surface and the corner region of lower surface and tail wind fairing, which is the main cause of VIV. This study provides a new way for the research on the mechanism of VIV, and can be applied to other cross-sections.