Research On Dynamic Behavior And Wrinkling Pattern Of Space Inflatable Membrane Structure

The Space membrane has the advantages of low manufacturing cost,small launch volume,light weight and high reliability.It can achieve outstanding performances which are difficult to achieve with traditional structures and has became a hot spot for space research and development.Its application on various types of spacecraft will be an inexorable trend in the development of space technology in the future.The inflatable expansion structure is a large flexible structure,and its dynamic-behavior is very complex,involving geometric non-linearity,material non-linearity and boundary condition non-linearity.It is a highly nonlinear coupling problem.The dynamic modeling and simulation analysis for inflatable expansion structure are still very difficult.The inflatable expansion structure is folded into a small volume during launching,and initial strain will be generated during the folding process.Since it is difficult to achieve a vacuum state,there will be some residual gas inside the structure after folding.The initial strain and residual gas will affect the reliability and accuracy of the space structure.The out-of-plane stiffness of the space membrane structure is small,and the folding phenomenon is one of the main defects of the space membrane structure during service.It will directly change the transmission path of the force in the structure,reduce its bearing capacity,and even lead to the complete failure of the entire structure.Therefore,based on the nonlinear dynamics theory,this work uses the theoretical analysis,numerical calculation and experimental verification research to conduct an exploratory study on dynamic behavior and wrinkling pattern of space inflatable membrane structure and provide theoretical basis and technical support to the engineering application of space membrane structure.In this research,the nonlinear finite element method for numerical simulation of inflatable expansion structures is introduced.Also,the stress hardening effect is considered;the stiffness matrix and equivalent joint force vector of membrane element are derived.The influence of the following pressure stiffness is considered in the modal analysis and dynamic response analysis of the inflatable expansion structure.Contact non-linearity is considered in the unfolding dynamics analysis,and the penalty function is used to solve the contact problem.The structural design of the full flexible and rigid-flexible inflatable spacecraft is proposed,and the dynamic characteristics and response behavior of these two structures were studied.Based on the nonlinear mechanics principle,the dynamics analysis model of inflatable spacecraft is established.The dynamic characteristics of the inflatable spacecraft were evaluated through prestressed modal analysis and harmonic response analysis.Under the external load,the spacecraft will be dominated by bending vibration.The dynamic behaviors of two types of inflatable spacecraft under impact loads were obtained by transient dynamics analysis and low-velocity impact analysis.The results show that the full flexible inflatable structure has good impact resistance,and the composite thin shell is safe during the collision.After the spacecraft structure is separated from the colliding objects the main motion form is the overall free vibration,and the local deformation caused by collision basically disappears.The necessary conditions of surface folding pattern design are studied.On this basis,the folding scheme of conical shell surface is designed: Four-fold-lines method,six-fold-lines method and the improved method.The fold-line layouts and relation formulas of the fold angles were determined.Thus the parameterized folding state of the conical shell surface is established.Based on the proposed model and Ansys/Ls-dyna software,the numerical analysis model of expansion dynamics is further established.The dynamic characteristics of the inflatable capsule structure in orbit under the ground environment were numerically simulated.Thus,the deployment configurations and the time history curves of the dynamic characteristics were obtained.The results indicated that under the ground environment,the inflatable capsule can be smoothly and gently expanded without large collision and physical interference,which proves the feasibility of the folding scheme.The effects of residual gas on the folding performance of the inflatable capsule were also analyzed.Under the action of residual gas in the inner cavity,the inflatable capsule would expand and maintain dynamic equilibrium before being inflated.It is difficult to fold and package the inflatable capsule with residual gas into a small volume,and it will result in waste of the mounting space.The numerical simulation and experimental investigation of wrinkles in laminated membranes were studied,Based on laminated thin-shell elements,the nonlinear post-buckling analysis method,was used to simulate the onset,growth and final configuration of wrinkles of laminated membranes under external loads.The numerical analysis model of laminated films was established,and the variation law of the wavelength and amplitude of folds in different development stages was analyzed.Devices were designed and developed that could be used to clamp and load laminated membranes in several load cases.A 3D photogrammetry system was constructed to characterize wrinkling patterns of laminated membranes,which subjected to shear displacement loads.By comparing the results of numerical analysis and experiment a good agreement was obtained,which verifies the accuracy and effectiveness of the numerical model.Furthermore,initiation and expansion the process hold of folds with the increase of external load level was studied.Various geometric characteristics of the folds in the early stage changed rapidly,but with the increase of load,the number of folds and the average half-wavelength changed little,only the z-direction displacement of folds increased.The effects of initial pretension,initial geometrical defects,film thickness and laminated film design parameters on the three-dimensional morphology of the fold were studied.The results indicated that initial pretension,film thickness and number of layers laid have great influence on the number and amplitude of laminated film folds.