Investigation of nonlinear and transitional characteristics of flutter varying with wind angles of attack for some typical sections with different side ratios

Abstract

This study conducted a comprehensive investigation into the flutter responses of three closed sections, namely two streamlined box girders and a 5:1 rectangular cylinder, which possess different side ratios. Different types of flutter were measured during the tests. The nonlinear and transitional characteristics of the flutter were thoroughly discussed. The effects of the wind angle of attack and side ratio on the reduced critical wind speed, limit cycle oscillation amplitude and the transition behaviors of the flutter were investigated. The complex modal motion information of the three systems was discussed. The main factors contributing to the transition of flutter, and the dynamic mechanisms of the occurrence of different flutter manifestations, were investigated. This was achieved by examining the evolution of their modal damping ratios with the vibration amplitude and wind speed. Finally, an examination was conducted to evaluate the impact of the mechanical damping ratio on the transition behavior of flutter as well as its effectiveness in mitigating flutter responses for the considered sections. Results showed that the various manifestations of the flutter are mainly ascribed to the gradually evolved modal damping ratio, where aerodynamic damping plays the most important role in producing different types of limit cycle oscillations and transitional behaviors of flutter. Moreover, the modal damping ratio slowly transitions with the wind angle of attack, wind speed, or the side ratio of a section, instead of experiencing any mutation, despite the observation of some distinct types of flutter during the tests.