Rotor Rubbing Research Articles

Fault diagnosis of new type screw compressor of helium liquefier by vibration signal

A diagnostic method for screw compressor faults using vibration signals was introduced and applied to a new type of helium oil-injected screw compressor in the 80L/h helium liquefier. The study revealed that the destruction of the oil film due to impurity particles could lead to rotor rubbing and poor meshing, compromising the reliability of these compressors. Based on frequency-domain analysis, the major vibration occurred at the meshing frequency of screw rotors and a series of its harmonics. The vibration of the characteristic frequency of bearing parts also indicated that the bearing had slight wear in the early stage. The vibration waveform’s time domain diagram exhibited clear clipping, and the axis trajectory shew disorder, which were common characteristic of rotor rubbing. When compressing helium with low molecular weight, the meshing clearance, tooth tip clearance, and end clearance of the rotor were significantly lower than those of traditional refrigerants or air media. Additionally, the thermal gap caused by thermoelastic deformation was smaller due to the large adiabatic index of helium. Therefore, rubbing faults between rotors and between rotors and casing were more likely to occur. The article recommended establishing a vibration signal monitoring system, optimizing the design of helium screw rotor profiles, and setting up reliability standards for screw compressor operation, such as limiting the vibration speed to ≤ 8 mm/s. Additionally, attention should be given to cleaning gas pipelines in cryogenic engineering and monitoring compressor vibration and noise signals during operation to prevent rotor damage due to particle impurities.

Generalized adaptive singular spectrum decomposition and its application in fault diagnosis of rotating machinery under varying speed

Rotating machinery fault signals often consist of multiple components with time varying frequencies under variable speed conditions. Spectral overlap exists among these components, making it difficult to independently separate the features of the components. Singular spectrum decomposition (SSD), a singular spectrum analysis-based signal decomposition method, has shown its great potential in suppressing background noise and extracting fault-related components in complex background noise environments. However, SSD is a frequency domain decomposition method with equivalent filtering characteristics, and it is susceptible to the mode mixing when processing signals with spectral overlap. Moreover, the choice of a key parameter in the iteration decomposition process of SSD, the embedding dimension, is determined using an empirical formula, which might cause suboptimal decomposition outcomes. To address these issues, this paper proposes a generalized adaptive singular spectrum decomposition (GASSD) method, which combines generalized demodulation with improved embedding dimension selection for SSD. GASSD incorporates SSD into the framework of adaptive generalized demodulation to separate specific frequency domain features. Firstly, for an effective generalized demodulation analysis, a region block synchronous ridge extraction method is proposed to accurately estimate the instantaneous frequency ridges from the time-frequency plane, which helps construct proper demodulation phase functions. Secondly, to achieve optimal analysis of SSD, a Gini moderation decomposition index is designed to improve the construction of the trajectory matrix by determining an appropriate embedding dimension. Finally, the reliability of the proposed method is demonstrated by analyzing wind turbine generator bearing fault signals and rotor rubbing fault signals.

Numerical and experimental analysis of stable, unstable, and limit cycle spiral vibrations

In rotating machinery, non-uniform temperature distribution or hot spots on the rotor surface can induce spiral vibrations. In this paper, a novel experimental apparatus is used to analyze the influence of a hot spot on the dynamic behavior of a flexible rotor supported by oil journal bearings. The hot spot is generated using an induction system with controlled amplitude and phase shift with respect to the vibration vector. Hence, it was possible to mimic phenomena like the Morton effect or the Newkirk effect. Different types of spiral vibrations were experimentally reproduced: stable, unstable and limit cycle. In the latter case, the vibration vector describes a closed loop when plotted in a polar plot. Therefore, the present work isolates the phenomenon of spiral vibrations from the complexity of the physics behind the generation of hot spot whether this source is the viscous shearing, rotor rubbing, or eddy current losses in magnetic bearings.Moreover, a theoretical model is derived to gain insight on the mechanisms driving spiral vibrations especially the role that the phase shift between the hot spot and the vibration vector plays in the stability of the system. Theoretical and experimental stability maps obtained for sub-synchronous and super-synchronous angular speeds are in excellent agreement. Additionally, the notion of thermal period, i.e., the period that govern the oscillation of the vibration vector is introduced. A concept never addressed before. It was found that this thermal period depends not only on the thermal inertia of the rotor, but also on the amplitude and phase shift of the hot spot, the distance to the critical speed and the damping ratio.

Analysis and Research on Vibration Characteristics of Nuclear Centrifugal Pumps Rotor Rubbing Fault

To investigate the vibration characteristics of nuclear centrifugal pumps rotor rubbing fault, the mechanical model of rotor rub is established, and the causes, types, and mechanisms of rotor rub fault are introduced. Taking the HAZ50-250 Type Horizontal single-stage centrifugal pump prototype as the object, through a reasonable test scheme, the vibration test and analysis of the rotor under different rub conditions were carried out using the Enpac2500 Dual channel spectrum analyzer, and the fault data of different rub impact degrees were collected. Combining the characteristics of vibration parameters such as time-domain, frequency-domain, and axis trajectory, it is found that the time-domain signal of rub fault shows an obvious “Top Clipping phenomenon.” The frequency-domain signal is mainly concentrated in one-time rotation frequency, two times rotation frequency, and a large number of nonlinear high harmonics. The axis trajectory will produce a concave image in the rub direction. In the actual rotor rub vibration fault diagnosis, it is necessary to comprehensively judge the vibration caused in combination with the operating state of the centrifugal pump, the state of the time domain, the frequency domain, and the axis trajectory. Based on the analyzed spectrum characteristics of the rub impact vibration, it is applied to the vibration fault diagnosis case of the centrifugal pump in the power plant, which timely prevents the pump damage and other faults caused by the deterioration of the rub impact fault, and plays a key role in the safe and stable operation of the centrifugal pump. It also provides an important reference for pump design and vibration fault diagnosis of rotating equipment in nuclear power plants.

Improved uniform phase empirical mode decomposition and its application in machinery fault diagnosis

As an adaptive non-stationary signal decomposition method, empirical mode decomposition (EMD) has a serious mode mixing problem. The uniform phase empirical mode decomposition (UPEMD) was proposed by adding a sinusoidal wave of uniform phase as a masking signal to overcome the shortcomings of EMD. However, the amplitude of added sinusoidal wave lacks adaptability, the mean curve cannot be completely separated from the signal in the iterative sifting process and thus the residual noise will affect the decomposition accuracy. To enhance the performance of UPEMD, in this paper, the improved uniform phase empirical mode decomposition (IUPEMD) method is developed to adaptively select the amplitude of added sinusoidal wave and then choose the optimal result from the iterative sifting of mean curves with different weights according to the index of orthogonality. The simulation signal analysis results show that IUPEMD has better decomposition ability and accuracy than the original UPEMD and ensemble empirical mode decomposition (EEMD). Finally, IUPEMD is applied to the rolling bearing and rotor rubbing fault diagnosis by comparing it with UPEMD, empirical wavelet transform (EWT) and variational mode decomposition (VMD) methods. The results show that IUPEMD can effectively identify the rolling bearing and rotor faults, and have better recognition effect than the comparison methods.

Identification of rotor-stator rub and dependence of dry whip boundary on rotor parameters

Rotor rub is one of the most critical and catastrophic event that occurs in gas turbine aircraft engines and other rotating machineries. Rotor rubbing introduces non-linearity in the system which makes the study of such phenomena difficult. The present study models a Jeffcott rotor along with a stator. This paper aims to develop a rotor rub model with Smoothening Function (SF) which can detect the onset of rotor rub efficiently whilst revealing the properties of Instantaneous Frequencies (IF) of rubbing rotor. First, the Adaptive Chirp Mode Decomposition Method (ACMD) has been used to detect the rub and establish the properties of IF. Next, the benefits of smoothening function in the rotor rub model have been discussed in terms of computation time. Further, the nonlinear dynamical behavior of the model has been studied using Poincare maps and Bifurcation diagram. The results reveal that IF of rotor possesses oscillating property which can be observed using ACMD method and can be used to detect the onset of rub. Moreover, use of SF effectively reduces the computation time by a factor of 11.6 when compared with classic rub model. The rotor orbits, Poincare Maps and Bifurcation diagram clearly shows that the rotor exhibits properties such as full annular rub, partial rub along with quasi-periodic motion. The presence of backward whirl using full spectrum has been observed and boundary for dry whip has been identified. Stability analysis using Floquet Theory reveals that the dry whip makes the rotor unstable. Dry whip boundary’s dependence on the parameters such as rotor stiffness ratio, damping ratio and friction coefficient has been discusses in detail.

Experimental Investigation on the Performance of Signal Processing Tools for the Analysis of Mechanical Vibrations in Rotor Rubbing

Rubbing is an important problem in machinery industry which occurs when a rotating element hits a stationary part. This rotor-to-stator rub may result in the catastrophic breakdown of the machine. In this work, the phenomenon of rotor rubbing is analyzed from the perspective that the signal analysis tools that are in use today to detect this defect emphasize or highlight particular aspects of the studied phenomenon. So, sometimes it is necessary to use more than one tool to deepen the understanding of the problem. For this purpose, laboratory tests were performed on a rotor system with a rubbing mechanism, while mechanical vibrations were measured with an accelerometer and a data acquisition system. Experiments were carried out for fixed rotor speed, and for run-up and run-down rotor speed conditions. The analysis approach included various processing tools to study their capabilities in rubbing detection: Root Mean Square (RMS), Fourier transform, Wavelet transform and Hurst exponent. Fixed rubbing conditions show similar results for RMS and Hurst exponent on the information obtained. For variable run-up and run-down rotor speed conditions, the Hurst exponent shows predictability, a fact that can be used for rub detection. However, the Wavelet and Fourier Transforms operated in a very distinct way. Although both transforms give frequency information, Fourier transform results in a more detailed frequency analysis, while the Wavelet transform can give time localization of the rubbing phenomenon.

Nonlinear Chirp Component Decomposition: A Method Based on Elastic Network Regression

Variational nonlinear chirp mode decomposition (VNCMD) is a recently proposed time-frequency analysis method that combines variational mode decomposition with the sparse representation framework. It can effectively decompose crossed and adjacent nonlinear chirp components. However, due to its optimization target's ridge regression characteristic, VNCMD cannot accurately reconstruct amplitude mutation components in fast-time-varying signals. Based on the framework of VNCMD and the sparsity and smoothness of Elastic Network Regression, we propose the nonlinear chirp component decomposition (NCCD) algorithm to decompose nonlinear chirps with strong piecewise linear characteristics accurately. We establish our new joint optimization model by adding weighted l <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> norm regulation term to the optimized objective function of VNCMD and solves the model by alternating direction method of multipliers. Meanwhile, we use the dynamic path optimization (DPO) algorithm to extract the time-frequency distribution ridge and initialize the instantaneous frequency. Simulation signals suggest that our method has higher decomposition accuracy for fast-time-varying nonstationary signals, smaller end effect, better convergence and noise robustness, and lower computational complexity. Furthermore, experimental signals of rotor rubbing suggest that our method can be more effectively applied to process strong modulation vibration signals than other methods such as synchrosqueezing transform (SST), synchro-extracting transform (SET), time reassigned-SST (TSST), and VNCMD.

Effect of the controllable support elements lubricated by magnetically sensitive fluids on chaotic and regular vibration of flexible rotors during rubbing

The proposed new rotor support element consists of a hydrodynamic bearing and a magnetorheological squeeze film damper. The damping is controlled by the change of resistance against the flow of magnetorheological fluid due to action of a magnetic field generated by electric current powering the electric coils. This paper deals with the study of the effect of the proposed support element on character of the rotor vibration during rubbing when impacts between the disc and the walls of a hole of square shape in the stationary part are induced. The system is excited by the rotor unbalance. The goal of the analysis is to investigate the effect of the applied current generating magnetic field on regularity of the rotor vibration. The results of the simulations show that the character of the vibration depends on speed of the rotor rotation and application of the current of right magnitude can change irregular oscillation into periodic and reduce magnitude of the impact forces. The proposed support element makes it possible to utilize all advantages of hydrodynamic bearings. The control of the damping effect is very simple as the damper can work only in the on/off regime. The performed study contributes to learning more on the design possibilities of suppression of undesirable phenomena induced by the rotor rubbing.

Vibration Analysis of a Rotating Flywheel/Flexible Coupling System with Angular Misalignment and Rubbing Using Smoothed Pseudo Wigner–Ville Distributions

Detection of early faults such as misalignment, rotor rubbing, shaft crack and bearing fault is necessary to avoid harmful and even catastrophic influences on rotating machinery. In this paper, the accelerating horizontal and pitching vibration responses of flywheel/flexible coupling model of an actual diesel generator, with angular misalignment and rubbing faults, are investigated using the smoothed pseudo-Wigner–Ville distributions (SPWVDs). Numerical simulations are performed through the dynamical equations of the flywheel/flexible coupling system; the results suggest that when an angular misalignment fault occurs, the super-harmonic resonance of order 3 can be found in the horizontal and pitching vibration signals. Meanwhile, both the 3fr and 5fr components (i.e., 3 and 5 times of the rotating frequencies) can also be found in SPWV distribution spectra. When rubbing fault occurs, more abundant sub- and super-harmonic frequency components can be observed in SPWV distribution spectra. Overall, the investigation shows that the smoothed pseudo-Wigner–Ville distribution spectra reveal obvious differences between the acceleration responses of the rotating system with different faults.

The Damping Capacity of Damping Devices during Rotor-over-Stator Rolling

The article presents results of investigating the influence of elastic damping devices that secure the rotor and the stator under high-amplitude oscillations under unfavorable development of an accident, e.g., upon rubbing of the rotor against the stator. Motion equations for the oscillations of the rotor in the clearance between the rotor and the stator and the oscillations of the rotor rubbing against the stator are written at adopted parameters of the stator considering not only the rigidity of the stator but also the energy losses under deformation of the stator components during the oscillations. Sudden unbalance of the rotor is taken as the initial excitation. A case of severe unbalance of the rotor is examined when, under oscillations accompanied by rubbing, the damping devices experience fairly severe strains in different rolling modes. The investigations were conducted using a rotor that had been affected by accidents accompanied by destruction of the bearings under rubbing in the absence of damping devices. A dynamic model of a symmetrical two-bearing rotor is considered. ADP-2400 shock absorbers served as dampers; the dynamic impact properties of the former had been determined using shock-testing machines. A possibility of the development of self-excited oscillations in the form of asynchronous rolling is considered depending on the absorption factor of the elastic damping devices. It is shown that no asynchronous rolling develops at definite absorption factor values. The oscillations of the rotor are restricted to the synchronous rolling at rotor–stator contact interaction forces that do not endanger the integrity of the turbine plant structure. The elastic damping devices with absorption factors above certain values eliminate the possibility of the development of self-excited oscillations in the form of asynchronous rolling and a practically unlimited increase in the rotor–stator interaction forces and, consequently, eliminate the danger of destruction (self-destruction) of the power-generating plant. In a sense, we can speak about the damping capacity of elastic damping devices during the evolution of an accident accompanied by rubbing of the rotor against the stator. The rigid mount of the stator on the foundation in the absence of damping devices increases the risk of the catastrophic development of the emergency considerably reducing the evolution time of the rolling and the possibility of using safety devices. A conceptual scheme that systemizes the general regulations for preventing TP accidents is provided.

Instantaneous Amplitude‐Frequency Feature Extraction for Rotor Fault Based on BEMD and Hilbert Transform

The vibration signals propagating in different directions from rotating machines can contain a variety of characteristic information. A novel feature extraction method based on bivariate empirical mode decomposition (BEMD) for rotor is proposed to comprehensively extract the fault features. In this work, the number of signal projection directions is determined through simulation, and the energy end condition based on the energy threshold is increased using BEMD to enhance the decomposition quality. Mixed vibration signals are generated along two orthogonal directions. Then, the acquired vibration signal can be decomposed into several intrinsic mode functions (IMFs) at the rotational speed using the BEMD method. Furthermore, the instantaneous frequency and instantaneous amplitude of the real signals and the imaginary part of the IMF signals are obtained using the Hilbert transform. The fault features along two and three dimensions can be investigated, providing more comprehensive information to aid in the fault diagnosis of rotor. Experimental results on oil film oscillation, the oil whirl, the bistability of the rotor, and looseness and rotor rubbing composite fault indicate the effectiveness of the proposed method.

Feedforward Chaotic Neural Network Model for Rotor Rub-Impact Fault Recognition Using Acoustic Emission Method

The rubbing faults caused by dynamic and static components in large rotatory machine are dangerous in manufacture process. This paper applies a feedforward chaotic neural network (FCNN) to recognize acoustic emission (AE) source in rotor rubbing and diagnose the rotor operational condition. This method adds the dynamic chaotic neurons based on logistic mapping into the multilayer perceptron (MLP) model to avoid the network falling into a local minimum, the delayed and feedback structure for maximum efficiency of recognition performance. The AE data was rotor rubbing process sampled from the test rig of rotatory machine, classification by fault degree. The experimental results indicate that the recognition rate is superior to the traditional BP network models. It is an effective method to recognize the rubbing faults for the machine normal operation.

Adaptive parameterless empirical wavelet transform based time-frequency analysis method and its application to rotor rubbing fault diagnosis

Empirical wavelet transform (EWT) is a novel method for analyzing the multi-component signals and is proposed based on the classical wavelet transform. To fulfill an adaptive separation of Fourier spectrum in EWT, the adaptive parameterless EWT (APEWT) method is proposed in this paper. To overcome the shortcomings of Hilbert transform in estimating the instantaneous frequency and amplitude, a quadrature derivative based normalized Hilbert transform (QDNHT) is put forward. In this paper the proposed time-frequency analysis method consisting of APEWT and QDNHT are compared with empirical mode decomposition (EMD), ensemble empirical mode decomposition (EEMD) and local characteristic-scale decomposition (LCD) and the comparison results have demonstrated the effectiveness of the proposed method. Finally, the proposed method is applied to the fault diagnosis of rotor system with local rubbing and the analysis results of experiment data indicate that the proposed method could effectively fulfill the fault diagnosis of rotor rubbing and show a better effect than EMD and EEMD methods.

Local rub-impact fault diagnosis of a rotor system based on adaptive local iterative filtering

When rotor rubbing occurs, the vibration signal comprises a periodic signal, a transient impact signal and noise. The main components of the periodic signal are the rotating frequency and harmonics thereof. The transient impact signal includes the rotor fault information. According to the characteristics of the local rub-impact fault in a rotor system, an adaptive local iterative filtering (ALIF) method is applied to fault diagnosis of the rotor local rub-impact. The ALIF method is used to decompose rotor vibration signals and can separate the rub, background and noise signals. The fault features of rotor local rub-impact can be extracted from the rotor vibration signal. A case study showed that the ALIF method can be effectively applied to the fault diagnosis of rotor local rub-impact.

Rotordynamic Behavior of 225 kW (300 HP) Class PMS Motor–Generator System Supported by Gas Foil Bearings

This paper presents the dynamic behavior of a 225 kW class (300 HP), 60,000 rpm, permanent magnet synchronous (PMS) motor–generator system supported on gas foil bearings (GFBs). The rotor of a 225 kW PMS motor is supported by two identical gas foil journal bearings (GFJBs) and one pair of gas foil thrust bearings (GFTBs). The total weight and axial length of the coupled rotors are 272 N and 1042 mm, respectively. During the speed-up test to 60,000 rpm, unexpected large subsynchronous rotor motions appear at around 120–130 Hz above 35,040 rpm. After disassembling the motor, an inspection of the top foils of the GFJBs reveals significant rotor rubbing. Thus, the GFJBs are redesigned to have a smaller load capacity by reducing their axial length to 45 mm. In addition, three 50 μm thick shims are installed in the GFJBs at 120 deg intervals for reducing the swirl speed of air and producing bearing preloads. The modification delays the onset speed of subsynchronous motions to 43,200 rpm and decreases the amplitude of the subsynchronous motions from 20 to 15 μm. These results indicate that the modification improves the stability margin of the high-speed rotor system with increasing stiffness and damping. In addition, the logarithmic decrement trends are in good agreement with the test results.

Normalized complex Teager energy operator demodulation method and its application to fault diagnosis in a rubbing rotor system

As a newer signal demodulation method composed of an empirical AM–FM decomposition and a Hilbert transform, the Normalized Hilbert transform (NHT) method has been proved effective to overcome several drawbacks of the direct Hilbert transform (HT) demodulation method to a certain extent, including limitation of Bedrosian theorem, negative frequency values and inevitable boundary fluctuations of the demodulation results. However, studies in this paper will show that the FM signal resulting from the empirical AM–FM decomposition may contain riding waves and its local extrema values may also deviate much from unity value in some cases. These two problems involved in the empirical AM–FM decomposition are not beneficial to extracting a desirable instantaneous frequency. Moreover, since the Hilbert transform is still used in the NHT method to extract instantaneous frequency from the FM signal, the boundary fluctuations will inevitably occur. Aiming at the drawbacks of NHT method, a new signal demodulation method named the normalized complex Teager energy operator (NCTEO) is proposed in this paper, which consists of an improved empirical AM–FM decomposition and a new instantaneous frequency estimate based on complex Teager energy operator (CTEO). In this demodulation method, the improved empirical AM–FM decomposition is firstly applied to a monocomponent signal for instantaneous amplitude extraction, achieving the separation of the envelope signal (AM part) and the carrier (FM part), then the proposed CTEO method is employed to extract the instantaneous frequency from the resulting FM signal. The results of comparative analysis on simulated signals and experimental rotor data demonstrate that NCTEO method can effectively extract the time-frequency information, and provide a reliable diagnostic basis for the rotor rubbing fault; moreover, comparisons with some other existing demodulation methods, such as HT, NHT and TEO methods, show the promising applications of NCTEO method.

Analysis The Rotor Rubbing Based on Parameters of Acoustic Emission

Analysis The Rotor Rubbing Based on Parameters of Acoustic Emission

Fault Diagnosis of Induction Motor Based on Wavelet Packet Analysis and Negative Selection Algorithm

For the spectrum characteristics of the motor vibration, the vibration fault diagnosis method of motor rotor rubbing based on wavelet packet transform and real-valued negative selection algorithm is put forward. Using wavelet packet analysis to energy analysis of rotor rubbing and extracting the fault feature vectors, then by real-valued negative selection algorithm to identify the normal and failure mode eigenvectors. The experimental results show that with this method all the rotor rubbing faults can be detected comprehensive and rapidly. This method has high feasibility of the wavelet packet analysis and real-valued negative selection algorithm in the rotor rubbing fault diagnosis.

Experimental Investigation of Rotor Rubbing Faults

Established a single-disc rubbing rotor system test-bench ,and can simulate the design of a single point of rubbing and rubbing of the rotor part. In the case of constant speed to ensure that observed in the rubbing rotor vibration under different conditions, the use of waveform, frequency spectrum, Orbit and other detailed analysis of the system before and after rubbing and chaotic properties of nonlinear response the experimental. results show that the occurrence rub rotor system, the system will stimulate a high frequency and fractional-octave, when there will be a serious rub chaos.