Numerical Analysis of an Air Spring with Two Tanks Connected by a Long Pipe (Effect of Orifice Installed in the Pipe)

Abstract

This paper deals with the numerical analysis of an air spring that consists of two tanks connected by a long pipe. Two resonance points may appear in the frequency response of a vibratory system supported by this type of air spring despite the fact that the system has an apparent single mass. This phenomenon is caused by the presence of a secondary mass as reported in our previous paper. It was found that the secondary mass is the mass of air which locally exists in the pipe. The magnitude of this mass is extremely small, but the acceleration of the air in the pipe ― and therefore the inertia force generated from it ― becomes very large. The generated force is further amplified by the Pascal’s principle and is transmitted to the supported mass. There are obvious nonlinear characteristics in this type of air spring; whereas the previous studies were based on linear assumptions. In this study, the governing equations for the air stream expressed by a nonlinear partial differential equation were solved by using the finite difference method. In particular, the pressure loss is evaluated due to air vortex being generated behind the orifice installed in the pipe. As a result of this study, it was found that the orifice is effective in suppressing the height of the secondary resonance point. Furthermore, this non-linear analysis provides the effective method to estimate the amplitude dependency of the dynamic characteristics of the air spring system.