Numerical identification of the dynamic characteristics of a nonlinear foil bearing structure: Effect of the excitation force amplitude and the assembly preload

Abstract

Modelling and identification of the dynamic characteristics of foil bearings under varying loads pose a great challenge and require the use of advanced numerical models. Although simple models can represent the structural characteristics of foil bearings with a certain degree of approximation, they are not able to reliably predict the properties of such a system over a wide range of external and internal loads. This is why the authors of this paper have undertaken to develop a model of the foil bearing structure, which would take into account all the most important phenomena affecting its dynamic properties. The model was developed using the finite element method, making it possible to represent the complex shape of the foil assembly and its geometric nonlinearity as well as the contact phenomena and friction, using static and kinetic friction coefficients. This model was verified experimentally and then used to identify the dynamic characteristics of the foil bearing over a wide range of loads, including different radial clearance and assembly interference. An original method of modelling the assembly preload is also proposed. The results confirmed that the parameters analysed have an enormous impact on the stiffness and damping coefficients. The presented methods can help other researchers assess the dynamic characteristics of a bump-type foil bearing structure. The presented structural model provides dynamic parameters that are necessary for a thorough analysis of the entire foil bearing.