流线闭口箱梁涡振过程气动力时频特性演变规律

Time-frequency evolutionary characteristics of multi-scale aerodynamic forces around the streamlined closed-box girder during vortex-induced vibration

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。立足于涡振发展完整过程中多尺度气动力(宏观整体涡激力与局部分布压力)与结构效应同步演变特性分析,从涡激气动力及其对结构行为作用机制角度揭示涡振机理。以典型大跨度桥梁流线型闭口箱梁断面为研究对象,实现了弹性悬挂节段模型同步测力、测振和测压风洞试验,精确获取了整体涡激力时频演变特征。对涡振过程风速关键结点模型表面气动力进行分析,可知箱梁整体涡激力特性在涡振发生前、锁定区上升区、振幅极值点、下降区以及涡振后等不同时期具有明显的变迁历程:上表面下游、下表面下游与下游风嘴转角区域分布气动力对涡激力的贡献、整体涡激力幅值等均与涡振振幅呈正相关关系,与涡振振幅同时达到最大。在锁定区内,涡激力高次谐波成分显著变化。在振幅极值点时,二次谐波成分与基波的比例最小。总之,涡振过程气动力特性与涡振响应同步演化,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,前者对整体涡激力起主要增强作用,而后者对整体涡激力起主要抑制作用,这些区域气动力是引起涡振的主要原因。

The mechanism of wind-induced vibration（WIV）is an important prerequisite for the evaluation and control of the vibration effects on bridges.Based on the synchronous evolutionary characteristics analysis of multi-scale aerodynamic forces and structural effects during WIV,the characteristic of vortex-exciting force（VEF）and its effects on structural behaviors are conducted in order to reveal the mechanism of VIV.Aiming at a traditional streamlined closed-box girder of long-span bridges,the wind tunnel tests of synchronal measurement of force and displacement responses of spring-suspended sectional model is conducted.The pressure-measuring tests are also implemented to acquire the integral time-frequency characterics of the VEF model during WIV.Then,time-frequency evolutionary characteristics of the VEF during WIV were compared among the pre-WIV period,ascent stage,amplitude extreme point,descent stage,and post-WIV period.It is found that the aerodynamic characteristics of the model varies dramatically with the velocities during WIV,which was obviously different from the lock-in period and the non-VIV period.There exists much larger contribution to the VEF in lock-in period than in non-VIV period near the downstream region of upper surfaceas well as the corner region of the lower surface and the tail wind fairing.The contribution of the aerodynamic forces to VEF and the amplitude of VEF are positively correlated with the amplitude of VIV responses.Additionally,the high-order harmonic components of VEF varies significantly during WIV,reaching its minimum value at the amplitude extreme point.In conclusion,the aerodynamic characteristics and the WIV responses during WIV are synergistic,especially near the downstream region of upper surface as well as the corner region of lower surface and the tail wind fairing,which contribute positively and negatively to VEF respectively and are are the main causes of WIV.