Aerodynamic Nonlinear Energy Evolution Characteristics of Vertical Vortex-Induced Vibration of Open Bridge Girder

Compared with traditional streamlined box girders, girders with a typical open section have a highly bluff aerodynamic shape and are prone to cause vortex-induced vibration (VIV), which will affect the safety and serviceability of a bridge. In this study, the surface pressure distribution and aerodynamic nonlinearity characteristics of a typical open section are studied through wind tunnel tests and numerical simulations. Based on the synchronous measurement technology, the evolution characteristics of the surface pressure distribution in different periods of the VIV lock-in region are analyzed, and the numerical simulation of the section was performed by a user-defined function (UDF) program. The numerical simulation results are in good agreement with the wind tunnel test results. Furthermore, the multi-order components of aerodynamic force in the VIV process were decomposed by the Hilbert vibration decomposition (HVD) method. Our study found that the average pressure of the open section's surface at the leading edge was negative, as this is where the air flow is separated. At the extreme point of the VIV lock-in region, the fluctuating pressure changes most drastically in the region (0.1 < X/B < 0.3), indicating that the intensity of vortex shedding is the greatest in this region. High-order components of the aerodynamic forces acting on an open section girder can be identified by analysis. The aerodynamic damping of the open section girder is significantly reduced in the VIV lock-in region, and reaches its minimum near the extreme point of VIV. Due to the presence of high-order harmonic components, the degree of aerodynamic nonlinearity continues to increase. Moreover, the work performed by each aerodynamic component throughout the whole vibration period has different characteristics, and the influence of the third-order and above components on the VIV system can be ignored. This study can help us to further understand the aerodynamic nonlinear energy evolution characteristics of the open section, and further improve people's understanding of the VIV system.