Numerical Study On Physical Mechanism Of Across-wind Aeroelastic Instability Of Flexible High-rise Structures

The wind-induced oscillation of flexible high-rise is a typical wind-structure interaction problem. In the process of the interaction, flow actions act as positive damp to the movement currently, but, they could transform to negative damp sometimes. If energy obtained from the flow exceeds the structure's damp, unstable aerodynamic phenomena would occur. The unstable aerodynamic phenomena is so-called galloping or flutter, and it can destroy structures in short-term. There have a lot of studies about unstable aerodynamics in recent years, but the physical mechanism isn't discovered now, because of its complication and limitation of study-means. The primary objective of this dissertation is to research the unstable aerodynamic characteristic and the physical mechanism of flexible high-rise with rectangular section by the Computational Fluid Dynamics (CFD).To introduce into the influence of the structure's oscillations, a computation domain and a physical domain are established in this research. The physical domain moves with the motion of the body at each time step, although that of computational domain is fixed. The original governing equations of fluid flow in the physical domain are transformed to the computational domain's coordinate system including time. The structure is reduced to a uniform rectangular cylinder, and is elastically mounted at the bottom. The governing equations of fluid flows and the equation of motion are alternately solved at each time step.With the convenience of nonstaggered grid system and the Smagorinsky model based on the structured orthogonal grid scheme, a computer program named WSSG is developed. Using the program can simulate the unstable aerodynamic characteristic and the physical mechanism of flexible high-rise with rectangular section. The program is employed in three-dimensional numerical simulation of wind flow.Using the developed computer program the wind flow around a static rectangular-section tall building is numerical predicted, firstly. It is proved that the mean pressure and the fluctuational pressure are computed accurately, and the flow structure can be simulated. Then, using the program the unstable aeroelastic oscillation of flexible high-rise is simulated. The galloping phenomena are achievedsuccessfully, and illustrate the physical mechanism by means of flow structure. The transition of oscillation from stable motion to unstable motion is studied. Finally, The influence of structure's elastic-parameter to the unstable motion is researched.