Key Issues Of Parameter Identification Of Empirical Nonlinear Model For Closed Steel Box Girders Undergoing Vortex-induced Vibration

Vortex Induced Vibration(VIV)is a typical flow-structure interference phenomenon which causes an unsteady flow pattern due to vortex shedding at or near the structure's natural frequency leading to resonant vibrations.VIV is an important issue in the aerodynamic performance of long span bridges,and is typically connected to premature fatigue damage and to the serviceability of a bridge.In this study,we mainly focused on the key issues of parameter identification of empirical nonlinear model for closed steel box girders undergoing vortex-induced vibration.A sectional model wind tunnel test was carried out to investigate the vortex-induced vibrations of a closed steel box girder.Vortex-excited force and displacement were extracted,utilizing complete synchronization method of identifying Scanlan's empirical nonlinear aerodynamic model.Based on the recurrence quantitative quantification analytical theory,the scale of data selection for vortex-excited force and displacement was optimized.A method of least squares was used to identify the aerodynamic parameters of Scanlan's empirical nonlinear aerodynamic model.Some tiny time delay was applied to account for the significance of synchronization of signal acquisition for VIV force and displacement in wind tunnel test.Research reveals that Scanlan's empirical nonlinear aerodynamic model is very sensitive to synchronization of VIV force and displacement.Also,we take the problem as a two-dimensional vibration system and reconstructed the whole process of VIV from oscillation starting to vanish.It is observed that the lock-in phenomenon was brilliantly realized by numerical methods.Although physically the VIV is usually occurred in three-dimensional bridge,we believe,as is supported by the agreement between calculated results and experimental data,that it can be reasonably well represented by this two-dimensional model.