Amplitude conversion of vortex-induced vibration based on #br#
generalized model of nonlinear vortex-induced force
Zhou Qi1 Meng Xiaoliang2 Zhu Ledong3
1. Guangdong Engineering Center for Structure Safety and Health Monitoring,Shantou University,Shantou 515063,China;
2. Shanghai University of Engineering Science,Shanghai 201620,China;
3. State Key Laboratory of Disaster Reduction in Civil Engineering,Tongji University,Shanghai 200092,China
Abstract：Wind tunnel test with a sectional model is one of the main methods to determine the lock-in region and the maximum amplitude of vortex-induced vibration (VIV). The amplitude of VIV obtained from the wind tunnel test should be modified and cannot be converted directly to its prototype bridge via the geometric scale ratio. Many researches have indicated that the vortex-induced force is characterized with the strong nonlinear behavior,and thus the conversion method based on a linear vortex-induced force model is no longer applicable. In addition,the existing conversion methods based on the nonlinear vortex-induced force model which is inaccurate may not be applicable,and they don’t provide the modification to the damping ratio. In view of the above,the generalized model of nonlinear vortex-induced force is derived by means of the dimensional analysis method. The simplified generalized model of vortexinduced force,which is only useful for amplitude calculation,is also presented. The amplitude conversion method of VIV between a sectional model and its prototype bridge is deduced by applying the principle that the equal energy input should result in the equal amplitude. The analysis results show that,although the nonlinear vortex-induced force models may be different,the amplitude conversion relationship remains the same. If the damping ratio of the sectional model equals to that of its prototype bridge,the conversion relationship only relates to the structural model shapes. If they are not equal,the conversion relationship not only relates to the structural model shapes but also to the change rate of amplitude during the decay-to-resonance period or growth-to-resonance period of VIV as well as the stable dimensionless amplitude of VIV. Compared to other conversion methods,the results obtained from the proposed method have better agreements with the field measurement results.
