A simplified structural model of bump-type foil bearings based on contact mechanics including gaps and friction

Abstract

Abstract The paper introduces a structural model for bump-type foil bearings based on contact mechanics including gaps and friction. The starting point is a model introduced in [32] were the bump foil is approximated by a specific structure of interacting springs. Following this model, contacts between the top and bump foils and between the bump foil and the sleeve are always closed. Recent analyses [31] showed that this not always verified: contacts can become loose even for very simple loading situations. A new model is then developed for considering these situations. The new model takes into account the elasticity of the top foil and three kind of gaps: between the rotor and the top foil, between the top and the bump foils and between the bump foils and the sleeve. The former model of the bump foil was extended by considering an additional degree of freedom per bump. Friction was modeled with Coulomb law. An efficient numerical procedure borrowed from contact mechanics ([41], [42]) was implemented for solving the structural problem with friction and close/loose gaps. The procedure uses the augmented Lagrangian algorithm for the normal contact forces and the penalty method for the tangential friction force. The procedure is very robust in dealing with stick-slip situations and close/loose contacts. The model was validated by comparisons with results from the literature ([31], [32]). By considering gaps in the foil structure and close/loose contacts, the model is not only closer to reality but can also handle manufacturing errors of the foil structure. This is shown by considering bump foil height manufacturing errors.