Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
Dynamics of a Rotor With Geometric Non-Linearity
Submission Author:
Rodrigo Nicoletti , SP , Brazil
Co-Authors:
Luís Fernando dos Anjos, Rodrigo Nicoletti
Presenter: Luís Fernando dos Anjos
doi://10.26678/ABCM.COBEM2021.COB2021-0068
Abstract
Rotating machines are usually modeled and analyzed by the finite element method. In such analyses, a linear behavior of the system is observed due to the linear nature of the modeling method. However, depending on the geometry of the rotor and on the level of external loading, nonlinear effects can appear, and the conventional finite element model is no longer appropriated (it cannot predict the nonlinear effects in the system). In this work, we study the nonlinear behavior of rotors with geometric non-linearity. The geometric non-linearity appears when large lateral displacements are imposed to the rotor. Due to the boundary constraints (restrictions imposed by the bearings), such large lateral displacements result in an axial loading, which increases the stiffness of the rotor (stiffening effect). In this work, we model a flexible rotor by the finite element method and we include in the model an additional stiffness matrix related to the geometric stiffening effect. The unbalance response of the system is analyzed for different levels of unbalance. The results show a clear bending of the resonance peak towards higher frequencies (stiffening effect) and, for higher levels of unbalance, the jump effect (sudden decrease or increase of vibration amplitude as we increase or decrease the rotating speed). We also show that hydrodynamic bearings tend to attenuate the nonlinear effects caused by the geometric non-linearity in comparison to the case using ball bearings.
Keywords
Rotordynamics, Finite Element Method, Centrifugally Stiffened Beam, nonlinear dynamics
