Modelling of a complex, nonlinear rotor system using 3D solid finite elements

The most common simulation approach in rotor dynamics consists in using beam-models. These models are usually very compact and come at low computational costs. However, they are afflicted with a number of limitations, making them insufficient for the analysis of more complex rotor systems, which require 3D solid modelling. General purpose FEM-codes offer full 3D solid modelling capabilities, but the question remains, whether they are capable of correctly taking into account the effects that arise from rotation. In the past, some well-known rotor dynamic specialists had their doubts about that, rightfully pointing out at several limitations of the codes. In the last few years, the codes of some of the most commonly used software have been updated, claiming to provide now extended rotor dynamic capabilities. The underlying paper provides an example of a complex, highly nonlinear rotor system, which cannot be simulated or even modelled accurately by using beam-elements, but rather requires solid 3D modelling. ABAQUS is used as a representative example for a general purpose FEM-code to build up an appropriate model. By doing so, the paper addresses the question, whether a general purpose FEM code is able to cover the necessary rotor dynamic effects. The derived model takes into account nonlinear stiffness behaviour, and includes contact between different components of a rotor assembly. The objective is to simulate a non-stationary run-up through a bending resonance, using direct time integration. The simulation results are compared to experiments, showing good consistency. During the crossing of the critical speed due to the bending resonance, mode-locking could be observed in the simulation and in the experiment.