Model Experiment And FEM Analysis Of Global Stability Of Natural Draft Cooling Tower

Stability is one of the important factors must be considered in the design of natural draft cooling towers.With the increasing of tower height,it is necessary to study the validity of the empirical formula adopted by the design specifications about the global stability of the cooling towers.Since it is difficult to get the analytical solutions for the global stability of the complex structure,the model test method and the finite element method are simultaneously used to study the basic law of the global stability of the cooling tower,therefore,providing some rational ideas and suggestions for the design of the cooling tower in the viewpoint of global stability.In this thesis,three scale models with different wall thicknesses are fabricated by 3D printing technology.The stability experiments are conducted in the wind tunnel by gradually increasing the wind speed,and the critical load of the experimental instability is analyzed with data fitting.The experimental results show that the deformations of the models before buckling are small and the models collapse suddenly,indicating that the global instability is nearly elastic.The ratio of wall thickness to throat radius is the key parameter to the critical load.The results obtained by the statistical analysis of the model tests are shown to be close to those introduced by the current design specifications.Meanwhile,the commercial finite element software ANSYS was launched to simulate the linear stability with perfect model,stability with initial geometric imperfections and nonlinear stability of the models,respectively.The buckling modes obtained by numerical simulations are found to be consistent with those observed in model tests.Furthermore,the coefficient through the data fitting of numerical results is found to be greater than those by experiments and current design standards.The critical load of the cooling tower structure is very sensitive to the initial imperfections.The influences of geometric parameters,such as tower height,throat height,bottom slope and elevation angle etc.,on the global stability of cooling tower are further discussed by the overall simulations of 98 actual cooling towers with different tower types.The results show that the critical loads of the all towers obey the same empirical formula of the existing design specifications.The coefficient obtained by the statistical analysis of the simulation results is about 2 times of the empirical formula introduced by the design specifications.Since the effects of initial geometric imperfections and other factors on the global stability are all included,and the safety factor is assumed to be 5,in the existing design specifications of cooling tower,the design of tower according to the existing design specifications is supposed to be safe considering the global stability.