扁平箱梁颤振后状态的振幅依存性研究

以舟岱通道大桥扁平箱梁断面为对象,通过节段模型风洞试验详细测试了该断面在风速超过颤振临界点后,振幅随风速变化的颤振后振动特性。基于变振幅的运动时程,阐释了气动阻尼、相位差及颤振导数等参数的振幅依存特性,提出了变振幅条件下的各参数的识别方法,指出了影响扁平箱梁颤振后特性的主要因素,并利用耦合颤振闭合解法进行了验证。研究结果表明：扁平箱梁在颤振后的振动过程中,气动阻尼具有明显的振幅依存性,相位差的振幅依存性较弱,振幅比基本不具有振幅依存性;颤振导数A₂^*随振幅变化而显著变化,是影响气动阻尼改变的最主要因素,其余颤振导数具有一定的振幅依存性,但对气动阻尼的影响较小。最后从气动阻尼随振幅变化的角度初步阐释了扁平箱梁在颤振后发生不同振动现象的动力学机理,并从气动阻尼曲线存在多个零点的角度解释了扁平箱梁在同一风速下具有多个稳定振幅点的可能性。

Characteristics of Amplitude Dependence of a Flat Box Girder in a Post-flutter State

The post-flutter characteristics of the amplitude of a flat box girder were investigated using sectional model tests in a wind tunnel when the wind speed exceeds the critical flutter speed. Amplitude dependence characteristics of aerodynamic damping, phase difference, and flutter derivatives were derived based on the measured time histories of displacements in the post-flutter state. A method for estimating aerodynamic damping, phase difference, amplitude ratio, and flutter derivatives, which are functions of vibration amplitude, was proposed, and the accuracy of the proposed method was demonstrated through a coupled flutter closed-form solution. Based on this method, the potential effects of each flutter derivative on the post-flutter state were highlighted, which helps in better understanding the dynamic mechanism in the post-flutter state. Results show that aerodynamic damping is severely amplitude-dependent, whereas the phase difference and amplitude ratio are nearly insensitive to the variability of amplitude. In addition, A₂^* shows a significant amplitude-dependent characteristic and is the greatest contributor to drive the system in the post-flutter state. By contrast, other flutter derivatives that contribute to changes in aerodynamic damping can be neglected. Finally, the dynamic mechanisms of the post-flutter phenomena in the test were interpreted from the aerodynamic damping varying with amplitude. The possibility of multi-stable amplitudes of vibration in the post-flutter state under a given wind speed was also discussed by exploring the multi-zero values of the aerodynamic damping curve.