Study On Vibration Characteristics Of Inflatable Membrane Structure Considering Gas Effect

As lightweight structure,the inflatable membrane structures have broad application prospects in the aerospace field.Inflatable membrane structures need to be filled with over-pressure for its supporting ability.In this paper,the over-pressure gas refers to a certain pressure of gas,especially over 10 k Pa.The vibration characteristics of the inflated membrane structure are easily affected by the internal and the external gas due to its light weight and high flexibility.These effects mainly including the prestressing stiffness effect,the pressure follower force effect and the gas-solid coupling effect.The prestressing stiffness effect refers to the prestress on the membrane material generated by overpressure gas,which affects the structural stiffness.The pressure caused by the overpressure gas is always perpendicular to the surface of the structure during deformation,and this force related with the deformation would affect the structural stiffness,which is the pressure follower force effect.The gas-solid coupling effect refers to the internal and external gas would vibrate together with the inflated beam,which would affect the structural vibration.In this paper,the pressure follower force effect and gas-solid coupling effect on the vibration characteristics of inflated membrane structure are studied,and the corresponding analytical model are established.These would provide a theoretical references and analysis models for the research on vibration characteristics of inflated membrane structures.Based on Timoshenko beam theory and virtual work principle,the inflated straight beam is assumed to be variable cross section,the vibration control equations considering the axial pressure following effect is derived by introducing the inflated pressure virtual work.The element stiffness matrix from the pressure follower force effect is analyzed,and the inflated straight beam elelment model considering the axial pressure follower force effect is established.Then,a vibration test platform of the cantilever inflated beam was built,and experiment verified the accuracy of the proposed model.The pressure follower force effect on the vibration characteristics of the inflated beam is studied,and obtain that the pressure follower force effect is necessary in the fundamental frequency analysis of the inflated beam.A pressure follower force effect factor is proposed to describe the influence of pressure follower force effect on the natural frequency.The influence laws of geometric parameters such as structural size and cone angle on the vibration characteristics is studied.When the curvature radius is the same order with section diameter of the inflated curved beam,the inflatable straight beam model would not be suitable for the analysis of the inflated curved beam.Using the virtual velocity method which considers the pressure virtual power,the vibration control equation of inflated curved beam including curvature related pressure follower force effect is derived.The in-plane and out-of-plane vibration analysis model including curvature related pressure follower force effect of the inflated curved beam is established by using Galerkin method,and the element stiffness matrix caused by the pressure follower forcr effect is given.Its accuracy are verified by comparison with the finite membrane element method and the finite beam element method.Finally,the three-dimensional analysis model of the inflated beam is established.The influence law of the curvature of the inflated beam on the vibration characteristics of the inflated beam is analyzed.Based on the theory of acoustic wave and non-moment shell theory,the coupled equations of the inflated beam and gas are derived by introducing the fluid-solid coupling boundary condition.The gas-solid coupling finite element analysis model of the inflated beam is established.Then,the model is used to analyze the influences of internal and external gas on the vibration characteristics of the inflated beam,and the results suggest that the impact of internal gas and external gas is almost the same.The influence laws of gas density,sound velocity and inflated pressure on the vibration characteristics of inflated beam are analyzed.The increase of gas density causes the decrease of the natural fresuencies.Furthermore,the natural frequencies of the inflated beam would decrease with the increase of the inflated pressure.This is because the increase of pressure would leads to an increase of the gas density in the inflated beam,and increases the added mass,which is greater than the increment of the structural stiffness from inflated pressure.The vibration characteristics of the inflatable support boom is studied.Firstly,a vibration test platform which could imitate the inflatable support boom under no gravity is built,and the vibration characteristics are tested.Then,based on the equivalent stiffness method,the quivalent stiffness of a non-uniform inflatable support boom which composed of a laminated aluminum film and an elastic reinforcing strip is obtained.The vibration characteristics of the inflatable support boom is analyzed by using the models considering the pressure follower force and the gas-solid coupling effect,respectively.Both models are further verified by comparing with the experimental results.It obtains that the deviation of the first four natural frequencies for neglecting the gas-solid coupling effect in the space environment is less than 2.6%.The effects of the parameters of the elastic reinforcing strip and structural style on the vibration characteristics of the inflatable support boom are studied.Finally,the inflatable support boom is designed as the main support structure of a membrane sail structure.The vibration characteristics of the membrane sail structure are studied.The natural frequencies of the membrane sail would substantial increases by connect the inflatable extension arm and the sail surface using hanging line.The researches in this paper can be applied to evaluate the vibration characteristics of inflatable beams,inflatable arches and inflatable rings,as well as the large-scale spatial structures such as inflatable skeleton airships,inflatable antennas and membrane aeroshell.The researches would provide a theoretical basis for the vibration characteristics design of the inflated membrane structure.