Study On The Effect Of Inner Air On The Mechanical Performance Of Cushions

Cushions are widely used in large span structures such as water cube due to its light weight,rich shape and small folding volume.When the cushion is in a state of force or vibration,the displacement generated by the membrane surface will change the internal pressure of the cushions,resulting in changes in the stiffness of the cushions,which further affects the deformation of the cushions,reflecting the characteristics of the interaction between the inner air and the external membrane.At the same time,due to the light weight of the membrane,the quality of the inner air is in the same order of magnitude as the quality of the external membrane,which will also affect the mechanical properties of the cushions.It can be seen that the inner air has a great influence on the mechanical properties of the cushions,and how to consider the role of the inner air in the inflated membrane structure is very important.The quantitative analysis of the inner air action is helpful to fully understand the static performance and dynamic performance of the cushions.In this paper,the static analysis and natural vibration characteristics of the cushions are analyzed by equivalent the inner air to potential fluid.Compared with the method of equivalent the inner air to the static boundary condition and assuming that the inner air satisfies the ideal air equation,the influence of the inner air on the static and dynamic performance of the cushions were studied.Based on the influence law of inner air,a simplified air-membrane coupling method was proposed,and its accuracy and accuracy under different influencing factors are analyzed and verified.The specific research of the paper are as follows :1)The ADINA software was used to establish the finite element model of the inflated membrane cushions.The inner air in the inflated membrane was equivalent to a potential fluid,and the static analysis and dynamic analysis of the cushions were carried out.Compared with the method of equivalent the inner air to the static boundary condition and assuming that the inner air satisfies the ideal air equation,the influence of the inner air on the mechanical properties of the inflated membrane and its variation with the initial internal pressure,membrane thickness,size,vector-span ratio were studied.2)By studying the variation law of inner pressure,volume and air density of the cushions under external static load,a simplified air-membrane coupling method was proposed.Compared to the potential fluid method,the rationality and accuracy of this method were verified.In the static and dynamic analysis,the accuracy of the simplified coupling method considering the effect of inner air is further studied under the influence of parameters such as size,vector-span ratio,film thickness and initial internal pressure.The results show that due to the mass effect of the inner air and the coupling effect with the external membrane,the inner air has a magnitude effect on the mechanical properties of the inflated membrane structure.In the static analysis,the displacement of the cushions will be reduced and the stress will be increased under the action of the inner air.In the analysis of dynamic characteristics,the effect of inner air will make the modal of the upper and lower membrane surface cooperative vibration,and the natural vibration frequency of the cushions decrease.The influence of inner air on the static and dynamic performance of the cushions increases with the increase of initial internal pressure and size,and decreases with the increase of film thickness and vector-span ratio.The simplified air-membrane coupling method proposed in this paper can accurately reflect the inner air effect of the cushions,and can be used for the finite element analysis of the inflatable membrane considering the inner air effect.