Study Of Unsteady Aerodynamic Characteristics Of Long-span Flat Roof Using LES

In recent years,long-span flexible roofs have been widely used in large-scale public buildings such as stadiums,airport terminals exhibition centers,in which membrane structure is a typical representative.This type of roofs are very vulnerable to dynamic wind action because of their lightweight and flexibility,and large oscillation could be excited.Meanwhile,the vibration of roof has significant effects on the flow filed around roof.This phenomenon is called the unsteady aerodynamic phenomenon.Many evidence shows that the unsteady aerodynamic phenomenon could promote the instability of longspan roofs.However,in the wind-resistance design of long-span roofs,wind pressure on rigid roofs are usually tested in wind tunnel for design of wind load,where the unsteady aerodynamic characteristics are usually ignored,This may lead to an under-estimation of the wind effect on flexible structures under strong wind resulting in potential hazards.Researches on the unsteady aerodynamic characteristics of long-span roofs are quite limited,and the mechanism remains unknown.Therefore,it is critically important to investigate the unsteady aerodynamic characteristics of long-span roofs.In this study,computational fluid dynamics(CFD)simulation method is used to study the unsteady aerodynamic characteristics of long-span flexible roofs based on existing theory and experiments.The main contents of this thesis are as follows:(1)Reveal the unsteady aerodynamic mechanism of long-span flat roofs in a quantitative way.CFD numerical simulation of steady and unsteady aerodynamic roofs is carried out based on the numerical simulation method of forced vibration.On the basis of verifying the accuracy of the numerical simulation,the characteristics of the unsteady aerodynamic parameters,flow field and structural vibration of the large-span flat roof model are analyzed.Correlation and the influence of structural vibration on the flow field,qualitatively analyze the characteristics and mechanism of unsteady aerodynamics of large-span flat roofs.(2)Quantify the interaction effects between characteristic turbulence,roof vibration,and incoming turbulence,and clarify the interaction mechanism.Based on the space-time characteristics analysis method,the self-excited components,characteristic turbulence components and incoming turbulence components in the flow field and wind pressure are distinguished,and the space-time coherence characteristics of the flow field around the roof and the wind pressure field are analyzed.,Quantitatively analyze the unsteady aerodynamic characteristics from the perspective of modal energy,and further clarify the flow field-structure interaction mechanism.At the same time,two modal decomposition methods,namely Proper Orthogonal Decomposition(POD)and Dynamic Mode Decomposition(DMD)are used for analysis,and the two methods are compared for unsteady large-span roofs.Applicability to aerodynamic problems.(3)Study the unsteady aerodynamic characteristics of the roof under different turbulence degrees.By analyzing the wind pressure,unsteady aerodynamic parameters and the characteristics of the surrounding flow field of a large-span flat roof under different incoming flow turbulence conditions,the influence of incoming flow turbulence on the unsteady aerodynamic characteristics of the roof was studied,and the vortex above the roof was analyzed.The convection velocity predicts the critical wind speed of the unsteady and unstable vibration of the roof under different turbulence conditions.