Influences of Hydrodynamic Forces on the Identification of the Rotor-Stator-Rubbing Fault in a Rotating Machinery

Abstract

Mechanical failures of a complex machine such as rotor widely used in severe conditions often require specialized knowledge, technical expertise, and imagination to prevent its rupture. In this paper, a model for analyzing excitation of a coupled lateral-torsional vibrations of a shaft system in an inviscid fluid is proposed. The model considers the recurrent contact of the vibrating shaft to a fixed stator. The simplified mathematical model of the rotor-stator system is established based on the energy principle. The dynamic characteristics of the fluid-rotor system are studied, and the features of rub-impact are extracted numerically and validated experimentally under the effects of the unbalance and the hydrodynamic forces. The main contribution of this article is in extraction and identification of the rub features in an inviscid medium which proved to be complex by the obstruction of the fluid and required the use of appropriate signal processing tools. The results through a synchrosqueezing wavelet transform indicated that the exciting fluid force could significantly attenuate the instability and amplitude of rubbing rotor. The experimental results demonstrated that for half the first critical speed, the subharmonic 1 / 2 × Ω and the irregular orbit patterns provide good indices for rub detection in an inviscid fluid of the rotating shafts. Finally, it is revealed that the instantaneous frequency extraction based on wavelet synchrosqueezing is a useful tool to identify the weak and hidden peak harmonics localised in the time-frequency maps of the fluid-rotor system.

Vibrations of Misaligned Rotor System with Hysteretic Friction Arising from Driveshaft–Stator Contact under Dispersed Viscous Fluid Influences

“…The higher harmonic resonance at 1× order (47.21 Hz) can be observed in the two unbalanced rotors. However, it is worth mentioning from the FFT spectral plot that the higher sup-harmonic frequencies, for example, 2×, 4×, 6×, etc., along with the 1/2× subharmonic, which usually arise due to the rubbing presence as indicated in [10,18], do not appear in this case. It is evident that the decomposition by FFT is not satisfactory enough as some irregular and imprecise fluctuations exist around the critical frequency levels.…”

“…The first dynamic response of the misaligned Cardan shaft is performed. To validate the proposed model in this study, the parameters for the numerical simulation are chosen to be the same as those of the experiment in [10], and the proportionality between ω and Ω is maintained for a wide range of Ω, which is the threshold (ω = Ω). To illustrate the numerical results, the following plots in Figures 7 and 8 are used.…”

“…Their analysis demonstrated that the critical speed and the whirling radius of a rotor decrease with an increase in liquid viscosity between the shaft and the cylindrical wall. In the same order of ideas, works relating to fluid-shaft interaction under the condition of breathing crack and rubs of a flexible shaft under the boundary layer excitation have been reported in [7][8][9][10][11]. Researches on the dynamic response of the misalignment rotor with specific faults exhibiting nonlinearity, such as breathing crack, rub, etc., on the driveline is limited.…”

Experimental Analysis of a Cracked Cardan Shaft System under the Influence of Viscous Hydrodynamic Forces

“…The work of [8] presented a state estimation method using ensemble empirical mode decomposition to identify the operating state of a cardan shaft in high-speed trains by collecting two sets of gearbox vibration signals. Most studies have concentrated on the behavior of mechanisms coupled to universal joints [9][10][11][12][13]. However, there have been many cases of failure associated with the malfunctioning driveshaft in practice, and a limited article can be found that addresses this specific topic of cardan shaft failure in a fluid medium [5,14].…”

“…The recently published numerical study of this model concluded that the vibration generated by Hooke's joint and the strong fluctuation of the connected rotors are proportional to the transient stiffness of the flexible drive shaft [4][5][6][7][8][9][10][11][12][13][14][15]. In the present experimental study of a cracked driveshaft interconnected via Hooke's joint, it is important to consider the effect of fluid properties, shaft geometry, and speed.…”