Nonlinear structural response in vortex-induced vibrations.

摘要

This study focuses on realistic structural response calculations under vortex-induced vibration. For calculating response associated with vortex-induced vibrations of a flexible cylinder a new model is used. This model considers the periodic wake as a nonlinear oscillator interacting nonlinearly with the body oscillator; parametric excitation is taken as the driving mechanism. This model represents the mechanism of' vortex-induced vibration that includes lock-in motion over a bandwidth, zones of instability for various frequency ratios, phase jump, hysteresis and bistability in structural response.;Numerical integration of the coupled model highlights the key characteristics of vortex-induced vibration due to nonlinear interaction between the body and the wake and is used to calculate the shortening of vortex formation length. The results show that the response is bistable and phase jump is observed.;Approximate analytical analysis using Method of Averaging of Krylov and Bogoliubov and Integral Equation Method and direct numerical integration provides the solution for the single degree of freedom model in order to get the structural response. Analysis of the model shows: there are two distinct levels of response, a significant phase jump during the mode transition, an amplification around the structural frequency, increase in resonance amplitude with decreasing structural mass and damping, a hysteretic behavior at both ends of the lock-in zone and high amplitude nonlinear damping. This is in accord with experimentally observed key characteristics for free vortex-induced vibration of cylinders.;This study suggests that the structural response due to vortex-induced vibration is nonlinear and parametric. This study is expected to have a substantial impact on the damping techniques for controlling tall building vibrations. Moreover, it is believed, the out come of the work will lead to consistent and realistic structural response calculations.