The Overturning Simulation And Optimization Analysis Of Metal Diaphragm For Space Propellant Tanks

Space propellant tank is composed of tank shell and metal diaphragm, which is mainly used to store and control propellant for space propulsion system. When it works, metal diaphragm is overturned to bring propellant off the tank under a certain pressure of pressurized gas. During this time, diaphragm experiences elastic-plastic large deformation process from upper hemisphere to lower hemisphere. Thus whether the diaphragm can reverse effectively and stably is the key factor to the tank property.According to different conditions, there are different types of metal diaphragm. In the dissertation, hemispherical metal diaphragm and cone cylinder diaphragm with stiffeners are studied using large deformation elastic-plastic finite element method, its reversing deformation process is simulated and parameter’s sensitivity is analyzed based on orthogonal table, the main contents are as follows:(1) In view of the metal diaphragm without stiffener, establishing 3D shell model of the hemispherical metal diaphragm by using nonlinear finite element software MSC.Marc. Deformation process of diaphragm is simulated and some performance indexes are established for it. The influence of size parameter’s sensitivity to the performance indexes is analyzed by range analysis based on orthogonal table and the best combination of size parameters can be also determined.(2) In view of the cone cylinder diaphragm with stiffeners, the reinforced part can be analyzed by solid finite element and the deformation process of diaphragm is simulated. Performance indexes can be adjusted through the analysis of the deformation process. The influence of stiffener parameter’s sensitivity to the performance indexes is analyzed by range analysis based on orthogonal table and the optimal combination of size parameters can be also determined.(3) With the optimal combination as the initial point, the minimum critical load and the minimum pressure fluctuation are used as the objective function respectively, the optimization design of the width and height of the stiffener is carried out by using the sequence two programming method.(4) In view of hemispherical metal diaphragm with heat shield, establishing 3D shell model with composite laminate, and the overturning process of diaphragm is simulated. The parameters of heat shield are analyzed by orthogonal table experiment to determine the influence of them on the overturning process of diaphragm with heat shield.Through the above research, the main conclusions of this paper are as follows:(1) The overturning of the metal diaphragm of the propellant tank can be divided into 3 stages: the elastic stage of pre-buckling, the stability overturning of the post buckling and the internal pressure of the last stage of turnover. Diaphragm parameters mainly affect the second stage of the overturning process.(2) In view of the metal diaphragm without stiffener, in the radius of pre-bending edge, tangent length and tangent cone angle, the tangent length is the biggest influence factor to the M of diaphragm, the maximum stress and critical load of diaphragm, the radius of pre-bending edge is the biggest influence factor to the diaphragm apex radial displacement and pressure fluctuation.(3) In view of the cone cylinder diaphragm with stiffeners, in the three geometric parameters of the height, width and number of stiffeners, the number of stiffeners has the biggest impact on the quality of stiffeners and diaphragm apex radial displacement; the height of stiffener has the biggest impact on the maximum stress and pressure fluctuation of diaphragm; the width of stiffener has the biggest on the critical load of diaphragm.(4) With the optimal combination as initial point and the minimum pressure fluctuation are used as the objective function, optimum analysis is made. After optimization, the pressure fluctuation is decreased by 7.4%. Before optimum analysis, the range analysis of orthogonal test to estimate the iterative process of optimization roughly, and the method can save energy and time for designers.(5) In view of hemispherical metal diaphragm with heat shield, through experiment analysis we can find that critical load and the thickness of heat shield is second order relation, critical load and the elastic modulus of heat shield is one order linear relation. The results are consistent with the conclusions of the theory research.