Flutter Mechanism of Flat Box Girder under Different Attack Angles
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摘要: 静风效应产生的附加风攻角对大跨度桥梁的颤振性能有着重要的影响，因此研究不同风攻角下主梁的颤振机理有重要意义.以扁平箱梁为研究对象，基于不同攻角下的颤振导数，采用双模态耦合解法掌握了颤振性能，继而通过分析气动阻尼、相位差和气动力幅值的变化研究了颤振机理.研究结果表明：在0°和3°攻角下，非耦合气动力为扁平箱梁断面提供了较大的正阻尼，颤振临界风速较高；在5°攻角下，非耦合气动力产生的正阻尼显著减小，使得耦合气动力产生的负阻尼迅速增加，导致颤振临界风速显著降低；耦合运动相位角增大是大攻角下气动负阻尼增加的主要原因，耦合气动力振幅则对颤振风速没有影响；此颤振机理表明大攻角下扁平箱梁颤振性能的弱化是由耦合效应增大引起，而非扭转运动产生的气动负阻尼引起.Abstract: The effect of an additional attack angle induced by aerostatic force on flutter instability of long span bridges is significant, thus the study regarding the flutter mechanisms of a flat box girder under different attack angles is important and necessary. Flutter derivatives have been identified using forced vibration devices and the critical velocities have been calculated based on the bimodal coupled flutter analysis method. Based on this analysis scheme, the roles of aerodynamic damping, phase lag, and modal frequency, which aid to better understand the flutter mechanism of the girder under different attack angles, are intensively analysed. The study results indicate that uncoupled aerodynamic forces provide energy to enhance the stability of the systems that result in a higher critical flutter speed at 0° and 3° compared with the speed at 5° The negative aerodynamic damping induced by the coupled force increases rapidly while the positive damping provided by the non-coupled force decreases significantly at 5° attack angle, which results in the weakened flutter performance. The phase lag of coupled flutter is the primary parameter for increasing the negative damping, and the effect of aerodynamic amplitude is negligible. The mechanism indicates that the weakening flutter performance of a flat box girder at large attack angle is increased primarily owing to coupled motion, not induced by negative damping generated in the torsional flutter.
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Key words:
- flat box girder /
- flutter mechanism /
- flutter derivatives /
- aerodynamic damping /
- flutter mode
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图 3 气动阻尼及模态频率随折算风速的变化
Figure 3. Flutter analysis of aerodynamic damping ratio and modal frequency
图 4 耦合气动力项及非耦合气动力项对气动阻尼的影响
Figure 4. Contributions of coupled and uncoupled terms to damping ratios
图 5 总阻尼及其子项随折算风速的变化规律
Figure 5. Total damping and sub-items varying with reduced velocity
图 6 case 1~3中相位差随折算风速的变化曲线
Figure 6. Phase lag varying with reduced velocity in case 1-3
表 1 计算参数和试验参数
Table 1. Parameters for calculation and tests
α1 case m/kg I/(kg·m2) ωα0/(rad·s-1) ωh0/(rad·s-1) ωα0/ωh0 0° 1 10.56 0.327 18.85 10.21 1.85 2 9.61 0.325 19.44 11.00 1.77 3 10.56 0.372 17.67 10.21 1.73 3° 1 10.56 0.327 18.85 10.21 1.85 2 9.61 0.325 19.44 11.00 1.77 3 10.56 0.372 17.67 10.21 1.73 5° 1 10.56 0.327 18.85 10.21 1.85 2 9.61 0.325 19.44 11.00 1.77 3 10.56 0.372 17.67 10.21 1.73 
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