流线型闭口箱梁大攻角颤振性能及演变机理研究

Flutter Performance and Evolution Mechanism Analysis of a Streamlined Closed-box Girder at Large Angles of Attack

强台风和山区风伴随的大攻角效应直接影响大跨度桥梁颤振安全性能。以某流线型闭口箱梁断面为研究对象,开展不同风攻角条件下的节段模型自由振动与强迫振动风洞试验,获取其颤振临界风速和颤振导数,结合二维两自由度颤振分析方法,探讨了大攻角对闭口箱梁断面颤振性能的影响及其驱动机理,并定义了自由度能量贡献值和名义扭转中心用于描述颤振形态。研究结果表明:闭口箱梁断面的颤振性能具有很强的攻角敏感性,颤振临界风速随初始风攻角变化显著,其直接力学原因是部分关键颤振导数的攻角非线性变化;随着初始风攻角增大,A2*导数出现由负转正的现象且符号改变时所对应的折算风速逐渐减小,导致扭转模态的非耦合项阻尼在颤振临界状态附近转变为气动负阻尼,恶化了断面的颤振性能;且随着初始风攻角的增大,结构的颤振形态逐渐由弯扭耦合颤振向纯扭转颤振发展,扭心前移现象减弱。

The flutter performance of long-span bridges is directly affected by the winds featured with large angles of attack(AoAs)in typhoon climates and mountainous areas.Flutter critical wind speeds and flutter derivatives of a streamlined closed-box girder under various initial AoAs were obtained by using free-vibration and forced-vibration wind tunnel tests of a sectional model.The flutter performance and evolution mechanism of the closed-box girder at large AoAs were investigated by using the two-dimensional 2DOF two-degree-of-freedom closed-form solution method(2D-2DOF)closed-form solution method.The energy contribution of the DOFs and nominal torsional center were defined to describe the flutter modality.The results show that the flutter performance of the closed-box girder is susceptible to the AoA.The flutter critical wind speed changes significantly with the initial AoA,which mechanically results from the nonlinear variation of some typical flutter derivatives with the AoA.As the initial AoA increases,the sign of A2*changes from negative to positive,and the reduced wind speed associated with the sign change becomes lower.This leads to results in the uncoupled damping term related to the torsional branch turns into becoming the aerodynamic negative damping near the flutter onset,and worsens worsening the flutter performance.Furthermore,the flutter modality turns converts from the vertical-torsional coupled flutter to the purely torsional flutter,and the shift forward phenomena of the torsional center becomes insignificant.