Study On Dynamic Stability Of Dry Gas Seal System Under S-shaped Bellows

Dry gas seal technology is a non-contact seal.The most important elastic support elements are generally spring,but the bellows have better overall performance.The spring is replaced by the metal bellows as the elastic support element of the dry gas seal,which not only has the advantages of high temperature resistance,not easy aging,tight structure and good axial buoyancy,but also can seal the system through the elasticity of the bellows.In this paper,nonlinear dynamic behavior of the Sshaped bellows diaphragm is studied.Firstly,the nonlinear large deformation problem of S-shaped bellows diaphragm is studied.The S-shaped bellows diaphragm is regarded as the combined structure of the circular plate with initial deflection by method of simulated shell.By nonlinear large deflection bending theory,the nonlinear large deformation of S-shaped bellows diaphragm is analyzed.The modified iteration method is used to solve the S-shaped bellows diaphragm with one end fixed and one end free under the boundary condition and the continuity condition respectively,and the quadratic nonlinear solution with high precision is obtained.The characteristic curves of deflection and load at different height and wavelength are drawn.Secondly,the nonlinear natural frequency problem of S-type bellows diaphragm is studied.The nonlinear dynamic variational equation and the coordination equation of S-shaped diaphragm under dynamic and static load were obtained by Hamiltonian principle.The maximum amplitude of the diaphragm is selected as the perturbation parameter,and the nonlinear natural frequency of the S-shaped bellows diaphragm with one end fixed and one end free is solved by the perturbation variational method.In its first approximate equations,linear natural frequency is obtained,in its second approximate equations,nonlinear natural frequency of the diaphragm is obtained.The relationship between dimensionless load and natural frequency under different conditions is analyzed.Finally,the nonlinear stability of S-shaped bellows diaphragm problem is studied.Using the nonlinear bending theory of thin shell,the nonlinear dynamic equations of the S-shaped bellows diaphragm under static-dynamic load are obtained.According to the boundary condition and continuous condition,the forced vibration equation of diaphragm nonlinear system is obtained by Galerkin.The conditions for bifurcation of the system were determined by using Floquet index,and the stability at the equilibrium point of the system was discussed.