Study On Dynamic Analysis And Wind-Induced Aerodynamic Instability For Membrane Structures

Along with the development of science and technology, a number of long-span flexible membrane structures with beautiful shapes and new structural systems are widely applied into the public architecture, for example, gymnasium, hangar and exhibition building etc. These structures are characterized by their lightweight and flexibility. The lack of bending rigid renders these structures susceptible to large deflections even under moderate loads. In some cases, the loads themselves will be deforming coherent. A nonlinear analysis is required to include these effects in the load analysis of such structures. Moreover, relatively small weight makes membrane structures are rather sensitive to wind-induced dynamic excitation, and air-structure interaction has dramatic influence on structure dynamic behavior. At the meantime, there are seldom studies on wind-induced vibration analysis of membrane structures, especially, with the investigation of aerodynamic instability. So it is important to study dynamic analysis and wind-induced aerodynamic instability of membrane structures in the field of engineering and theory research, which include the effects of air aerodynamic force.This dissertation deals with the interaction between air and structure by means of a simplified aerodynamic force model, which is consisted of added air mass, radiation damping and pneumatic stiffness. And then, further investigation of the free and forced harmonic vibration is carried out considering membrane immersed in air. Meanwhile, the alteration and the influence regularity of aerodynamic forces dynamic characteristics of membrane structures have been studied according to theoretical derivation and numerical examples, which further quantify the coupling interaction between the surrounding air and structures.Based on the finite-element method, this dissertation employed the 3D solidacoustic elements of standard FE analysis software to simulate the air influence. Air is assumed as compressible, inviscid and potential, According to the mechanical characteristics of membrane structures, coupling kinetic equation of the air-structures interaction is established. Results obtained by the FE computation are compared with experimental results for a vibrating cable-membrane, which verify the valid of the method. And then, the free and forced harmonic vibration problems considering the geometrical nonlinear of the membrane structures have been studied in the present study. Meanwhile, the factors which affect dynamic response of the membrane structures in air fluid are discussed.Analysis of wind-induced dynamic response is a key problem for wind resistance design of membrane structure, in which the achieving of wind load and how to consider the interaction between the surrounding fluid and the membrane are very difficult. Based on the AR method the wind loading of an open hyperbolic membrane structure is simulated, and wind-induced response analysis in the time domain are calculated after building the membrane FE model with air domain. Moreover, it is difficult to obtain the wind loading time history by wind tunnel test of aeroelastic model because there have some limitation on test skill and conditions in the wind tunnel test. So, in order to seek a theoretical break through, applying the method to a flat membrane roof structure and using its wind tunnel test results, nonlinear wind-induced dynamic response analysis for such geometrically nonlinear roofs, which includes roof-air coupled model, is investigated. Finally, some valuable results are obtained.Because of the lightweight mass of membrane, the surrounding air interacts with membrane under wind loading and induces obvious aeroelastic response in structures. There may be occur aerodynamic instability phenomena when wind velocity reaches a certain magnitude. Now, there have proceeded a large number of research works on line shape structures such as tall buildings and large span bridges. But the progress of aerodynamic stability and critical wind velocity for membrane structures are still very slow. The governing equations of membrane roofs are obtained by applying large deflection membrane theory of thin shells, and the potential flow theory and the thin airfoil theory in aerodynamics are adopted to define the aerodynamic force on roof surface. Thus, the dynamic governing equations of wind-roof interaction for closed membrane roofs are established. The critical wind velocity of aerodynamic instabilityand its corresponding conclusions are achieved.Membrane structures usually have complex configuration. At the same time, membrane structures are often opened in the practice, so the study simulates membrane figure with traveling wave. Then the instability type and phase of membrane are investigated according to Bernoulli equation and Galerkin method. Further vortex sheet on membrane is used to substitute the infinitesimal thickness boundary layer between wind and membrane surface. The aerodynamic force was deduced after take account into the wake vortex sheet on the trailing edge of structure. Expression of aerodynamic force is obtained; meanwhile, finite sinusoidal waveform is employed to simulate kinetic shape of membrane approximately. The maximum amplitude of membrane during vibrating is solved according to Hamilton principle and Newton's iterative method. Dynamic equilibrium relationship is established based on the relation between aerodynamic force with dead weight and inertia force of membrane. Based on the foundation of above study, further critical instability wind velocity was found. Finally, the mechanics and change variation regularity between critical wind velocity and structure parameters are studied.