Analysis of a complete model of rotating machinery excited by magnetic actuator system

Abstract

Rotating machines have a wide range of application involving shafts rotating at high speeds that must have high confidence levels of operation. Therefore, the dynamic behavior analysis of such rotating systems is required to establish operational patterns of the equipment, providing the basis for controller development in order to reduce vibrations or even to control oil instabilities in lubricated bearings. A classical technique applied in parameter identification of machines and structures is the modal analysis, which consists of applying a perturbation force into the system and then to measure its response. However, there are mainly two problems in modal analysis concerning the excitation of rotating systems. First, there are limitations to the excitation of systems with rotating shafts when using impact hammers or shakers, due to friction, undesired tangential forces, and noise that can be introduced in the system response. The second problem relies in the difficulty of exciting backward whirl modes, an inherent characteristic from these systems. Therefore, the study of a non-contact technique of external excitation, also capable of exciting backward whirl modes, becomes of high interest. In this sense, this article deals with the study and modeling of a magnetic actuator, used as an external excitation source for a rotating machine, mainly in backward whirl mode. Special attention is given to the actuator model and its interaction with the rotor system. Differently from previous works with similar proposal, which uses current and air gap measurements, here the external excitation force control is based on the magnetic field directly measured by hall sensor positioned in the pole center of the magnetic actuator core. The magnetic actuator design was completely developed for this purpose, opening different paths to experimental application of this device, for example, fault detection analysis based on directional modes. It is also presented a comparison between the numerical simulations and practical tests obtained from a rotor test rig and an experimental evidence of the backward whirl was accomplished based on the numerical simulation results.