Nonlinear self-excited forces for a bluff body in post-critical galloping

Self-excited aerodynamic forces during transverse galloping oscillations have not only nonlinear characteristics but, despite the high reduced wind velocity, may also present significant unsteady features. In this study, the characteristics of the lateral self-excited force for a bluff body in post-critical galloping are analysed in depth by inspecting force hysteresis loops obtained through CFD simulations. It is found that nonlinear characteristics become prominent with increasing vibration amplitude, while unsteady features remain significant at any vibration amplitudes. The mathematical model based on amplitude-dependent flutter derivatives is introduced for the unsteady galloping phenomenon, and it can be used in calculations of critical wind speed as well as post-critical response. In addition, the aerodynamic damping contour is calculated based on the force model, and it can be used to easily forecast the amplitude-wind speed curve of the bluff body with nonlinear structural damping.