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COBEM 2023
27th International Congress of Mechanical Engineering
An investigation of wave propation in rotating shafts with attached disks
Submission Author:
Gilberto de Sousa Pinheiro Filho , DF , Brazil
Co-Authors:
Gilberto de Sousa Pinheiro Filho, Adriano Todorovic Fabro, Laís Bittencourt Visnadi
Presenter: Gilberto de Sousa Pinheiro Filho
doi://10.26678/ABCM.COBEM2023.COB2023-0378
Abstract
Vibration in rotors affects the performance and lifespan of several systems, like gas turbines, oil pumps, and high-speed electrical motors. With an ever-increasing demand for greener and more efficient machinery, the size and speed of rotors also tend to increase, exacerbating the aforementioned problems. Several methods of vibration control have been applied to address these issue, such as precise balancing and high-performance bearings. They are very effective and have been widely applied but have limited performance for the increasingly lighter and higher rotating speed designs of rotating machines. The gyroscopic motion present on rotors generates helical waves combining bending waves of both orthogonal directions. They whirl and vibrate on different frequencies depending on the type of forward or backward excitation. These gyroscopic effects have to be taken into account on the design and vibration control strategies of rotating machines. One promising area of research on this topic is the rotating metamaterials, which can be tuned to affect the specific response to forward or backward excitation in different frequency bands. However, the dynamics of such systems still lacks further investigations. This work presents wave propagation analysis of a rotating system composed of a shaft with attached disks. The investigation is carried out using a spectral element model which assumes a Timoshenko beams model for the shaft and thin disks for the rotors. The wave analysis assumes an infinitely long shaft with periodic attachments and a finite length model assumes journal bearings at both ends as lumped spring dampers with set stiffness and viscous damping. The focus of the investigation is on the symmetry of positive and negative going waves as well as on the generation of attenuation bands, or band gaps, on the dispersion curves. It is shown that the helical waves propagating in the system are not symmetrical, as expected, and the appearance of forward or backward waves depends on the forcing function for the finite length system. Moreover, the case of multiple rotors evenly attached to the shaft is also investigated. In this case, a bandgap is generated, which is expected, since the system resembles a metastructure. In conclusion, it is shown that utilizing a metamaterial approach can be an effective way of controlling vibrations on those systems, but the suitable wave behaviour must be considered for the design of the vibration control strategy.
Keywords
wave propagation, Rotordynamics, metamaterial, Vibration control, spectral elements
