Rubbing Fault Research Articles

Rub-impact investigation of a bolted joint rotor-bearing system considering hysteresis behavior at mating interface

Hysteresis behavior at the mating interface can induce nonlinear stiffness and frictional dissipation, which may lead to a complex vibration character, self-excited vibration, and even the rubbing fault for the bolted joint rotor system. The present work aims to investigate the effect mechanism of hysteresis behavior on the rotor dynamics and the mechanism of bolted joint performance change induced by a rubbing fault. Firstly, the bolted joint model considering the hysteresis behavior at the mating interface is proposed based on the Iwan model. Then, a non-dimensional dynamic model of the bolted joint rotor system with rubbing fault is established by combining the lumped-mass method and fixed-point rub-impact force model. After that, the nonlinear response of the bolted joint rotor system considering the hysteresis behavior at the mating interface and the effect of rubbing fault on the dynamic performance of such a rotor system is explored. Finally, an experimental verification is carried out by adopting a rotor system test rig with a different stiffness rubbing device. The result shows that the rubbing fault will reduce the critical speed by changing the equivalent average stiffness of the bolted joint and aggravate the self-excited vibration of the system, leading to a stronger nonlinear performance of the rotor system. The outcome of the present work can provide valuable insights into vibration prediction, health detection, and rubbing fault diagnosis for a rotor system with a bolted joint.

Investigation on dynamic rubbing characteristics of a bladed rotor system with multi-mode rubbing fault

Dynamic behavior analysis of blades under high cycle fatigue with rubbing fault is vital for estimating the reliability of rotating machinery. This paper focuses on a novel rubbing model and the flexible dynamic characteristics of a shaft-blade-disk system (SBDS) model with considerations of various forms of rub-impacts. Firstly, the deformation relations and the motion equations of the SBDS model in steady state are derived using Lagrange's principle. Secondly, a new quasi-static blade rubbing model involving shaft deformation and blade coupling effect is established, and the influence of rub-impact correlation parameters on rubbing force is further explored. Then, both the effect of shaft-disk coupling on the blades at various states and the dynamic characteristics of numerous rubbing modes are also investigated. The results revealed that the asymmetric form of rub-impact will induce more complex vibrational behavior (such as frequency components and trajectory differences), while the symmetrical rubbing modes can keep the system relatively stable.

Dynamic characteristics analysis and vibration control of coupled bending-torsional system for axial flow hydraulic generating set

Aiming at the vibration problems of shaft system for axial flow hydraulic generating sets caused by complex excitations, the coupled bending-torsional dynamic equations of rotor-runner system are established considering multi-effect including hydraulic, mechanical, electrical and other external vibration sources. Whether taking the torsional degree of freedom into account, the stability and disparate destabilization laws of system periodic solutions are analyzed using the shooting method combined with Floquet theory. On this basis, the influence of coupling bending-torsional effect on system dynamic behaviors is discussed through bifurcation diagrams, Poincaré maps, trajectories, time domains and frequency spectrums. Furthermore, in order to alleviate the unsteady vibration of rotor as well as runner, the magnetorheological fluid damper is introduced into the shaft system, and numerical simulations are performed on models of coupled bending-torsional systems with or without the magnetorheological fluid damper. The analyses indicate that the interaction between bending and torsional vibration of the shaft system will expand the chaotic sustained range for rotor. Meanwhile, the amplitude of the rotor-runner system is magnified owing to the torsional vibration, which leads to local rubbing faults of the system under specific operating conditions, while the intervention of the magnetorheological fluid damper can significantly suppress the nonlinear motion of rotor and runner, reduce the amplitude of system vibration, so as to avoid the occurrence of friction defects effectively. The above research results can provide conducive references for fault diagnosis, optimized design, and vibration control of axial flow hydraulic generating sets.

Vibration characteristics of blade-casing rubbing fault considering rotor–stator coupling

Blade-casing rubbing is a typical fault of aero-engine, but due to the complex structure of the equipment, it is still challenging to diagnose. This paper studies the characteristics of rubbing faults under rotor stator coupling. Firstly, a numerical model, which includes the rotor, bearings, and casing with blades, is constructed. Secondly, simulate the rubbing fault by setting the non-uniform initial gap between the blades and the casing, and the vibration response of the rotor and casing is obtained. Thirdly, combined with the test rig, the vibration characteristics under rubbing fault are verified. Finally, additional theoretical research is conducted on the vibration characteristics of the rotor, casing and blades under different degrees of rubbing fault. Theoretical and experimental results indicate that rubbing faults have different effects on the vibration of the rotor and stator: the rotational frequency amplitude of the rotor decreases while the frequency amplitude of the stator increases. As the fault degree increases, these phenomena become more significant. When rubbing faults occur, the harmonics near the system’s natural frequencies are more affected than the others. Moreover, rubbing faults can also cause the vibration of the rotor to be affected by the blade mode. The conclusions obtained in this paper can provide a reference for diagnosing rubbing faults in aero-engine.

Rub-impact dynamic analysis of a dual-rotor system with bolted joint structure: Theoretical and experimental investigations

Large gas turbines often utilize dual-rotor structures to improve efficiency. To facilitate manufacture and maintenance, the large rotor systems are typically constructed by connecting components made from different materials together through the bolted joint. In this work, a dynamic model of a dual-rotor system with bolted joint included in the high-pressure (HP) rotor is established based upon the finite element theory of Timoshenko beam element, as well as taking into account the bearing forces and fixed-point rubbing fault. To evaluate the influence of rubbing faults on the dynamic behavior of a dual-rotor system, this study analyzed the response characteristics of the rotor under the cases of the LP rotor and the HP rotor subjected to the rubbing fault, respectively. In order to further reveal the effect of bolted joint structure on the system response while rubbing fault occurs, piecewise linear bending stiffness is also considered in this study. The nonlinear vibration responses of the bolted joint dual rotor-bearing system are studied through numerical simulation. Effect of rotor–stator contact stiffness and the occurrence of rubbing faults at the low-pressure (LP) rotor and the HP rotor are investigated through frequency-amplitude curves, waterfall diagrams, time-domain responses, and bending stiffness of the bolted joint. The results indicate that the presence of rubbing faults, whether occurring at the LP rotor or the HP rotor, leads to a decrease in the critical speed. Furthermore, under a rubbing fault, the bending stiffness of the bolted joint enters the stiffness softening region earlier and exhibits a wider range, which is exacerbated with increased contact stiffness. This phenomenon is considered one of the main causes of system response instability. Finally, the experimental studies are carried out on a bolted joint dual-rotor test rig to validate the numerical simulation results.

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.

Dynamic Analysis of a Bolted Joint Rotor-Bearing System with a Blade–Casing Rubbing Fault

Bolted joints are widely used in aeroengine rotor systems to connect multiple components into an integrated structure and provide sufficient stiffness. The mechanical properties of a bolted joint have a significant effect on rotor dynamics. For modern aeroengine designs, the blade-tip clearance is gradually reduced to improve efficiency, which may lead to rubbing damage and affect safe operation. The mechanical properties of a bolted joint change significantly during the blade–casing rubbing process and influence the dynamic properties of the rotor system. Based on the finite element (FE) modeling method, a 15-node bolted joint rotor system model is established in this paper, in which the bolted joint is represented by a 2-node joint element, and the blade–casing rubbing force is considered. The Newmark method is used to solve the motion equations. The dynamic model is validated by comparing the frequency response characteristics for different numbers of blades with the results provided in other published studies. Based on the established model, the effects of the rotational speed, number of blades, and rubbing stiffness on the dynamic responses, normal rubbing forces, and bending stiffness of the bolted joint are evaluated by numerical simulation. The results show that the response amplitude and bending stiffness of the bolted joint change significantly under blade–casing rubbing faults, and the mean value of the vibration response deviates significantly from 0 as the number of blades increases. Meanwhile, the amplitude of the frequency component fVC and the maximum value of the normal rubbing force also increase as the number of blades increases. The main contribution of this paper is the establishment of a new model for a bolted joint rotor system, considering the time-varying bending stiffness of the bolted joint and the blade–casing rub fault, comparing the simulation results to obtain some general results bridging the current research gap. Meanwhile, the numerical results in this paper can provide a cognitive basis for the blade–casing rubbing fault mechanism of a bolted joint rotor system under the influence of speed, number of blades, and rubbing stiffness. The nonlinear dynamic characteristics observed in the present paper can be applied to the blade–casing rubbing fault diagnosis of turbomachines.

Bifurcation Analysis of a Rotor-Casing Coupling System with Bolted Flange Connection under the Effect of Rotor-Casing Rubbing Fault

This study mainly investigated the nonlinear vibration performance of a rotor-casing coupling system containing a bolted flange connection. The dynamic equations of the coupling system were developed while considering the radial stiffness of the bolted flange structure, which contained a spigot, squirrel cage with ball bearing, and rotor-casing coupling vibration. To study the influence of the disk casing fixed-point rubbing fault on the coupling system’s nonlinear dynamic performance, an analytical model of the nonlinear impact forces was established, which considered the contact and vibration responses of the rotor and casing. The frictional force was obtained based on the Coulomb friction law. The iterative analysis of motion equations was performed utilizing the Newmark method. Then, the nonlinear dynamic behaviors of the coupled systems were examined using data, including a bifurcation diagram, spectrum plot, greatest Lyapunov exponents, etc. The effects of rubbing fault on the dynamic properties of system were investigated in detail, indicating that there were various motion states, which were described as periodic, multi-periodic, and quasi-periodic motions. Comparing the simulation results, it was found that rubbing fault seriously affected the motion stability of the rotor system. Finally, by gathering and examining the vibration data set from a test platform for rotor-casings with bolted joints, the correctness of the numerical simulation findings was confirmed. Additionally, the results of the experimental investigation agreed with that of the simulation. The dynamic distinguishing characteristics that were noticed can be used as an indicator for determining whether the fixed-point rubbing fault between the rotor and casing has become worse.

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.

Bifurcation and Stability Analysis of a Bolted Joint Rotor System Contains Multi-Discs Subjected to Rub-Impact Effect

In aero-engines, the rotor systems are frequently designed with multistage discs, in which the discs are fastened together through bolted joints. During operation, rotating machines are susceptible to rotor–stator rubbing faults. Those bolted joints are subjected to friction and impact forces during a rubbing event, leading to a dramatic change in mechanical properties at the contacting interfaces, influencing the rotor dynamics, which have attracted the attention of scholars. In the present work, a mathematical model, which considers the unbalance force, rotor dimensional properties, nonlinear oil-film force and rub-impact effect, is developed to study the bifurcation and stability characteristics of the bolted joint rotor system containing multi-discs subjected to the rub-impact effect. The time-domain waveforms of the system are obtained numerically by using the Runge–Kutta method, and a bifurcation diagram, time domain waveforms, spectrum plots, shaft orbits and Poincaré maps are adopted to reveal the rotor dynamics under the effect of the rub-impact. Additionally, the influences of rubbing position at the multi-discs on rotor dynamic properties are also examined through bifurcation diagrams. The numerical simulation results show that the segments of the rotating speeds for rubbing are wider and more numerous, and the middle disc is subjected to the rub-impact. When the rub-impact position is far away from disc 1, the rubbing force has little effect on the response of disc 1. The corresponding results can help to understand the bifurcation characteristics of a bolted joint rotor system containing multi-discs subjected to the rub-impact effect.

Bifurcation studies of a bolted-joint rotor system subjected to fixed-point rubbing fault

Bifurcation studies of a bolted-joint rotor system subjected to fixed-point rubbing fault

Vibration analysis of a multi-disk bolted joint rotor-bearing system subjected to fixed-point rubbing fault

This study aims to investigate the nonlinear vibration properties of a rotor-bearing system carrying a multi-disk bolted joint with a fixed-point rubbing fault. For this purpose, a mathematical model of a multi-disk bolted joint rotor system is explored to determine the effect of rotor-stator rub-impact and rub-impact positions on the nonlinear dynamics of a certain type of aero-engine compressor. First, the dynamics of the rotor system with a rubbing fault are examined numerically. Then, the effect of the rub-impact position in the multi-disk bolted joint on the nonlinear dynamics is studied. The shaft is modeled using a massless shaft, where the stiffness matrix of the shaft is determined based on the flexibility influence coefficient method. The governing equation of the multi-disk bolted joint is deduced considering both the lateral and bending stiffness between the adjacent disks. The dynamic model of the overall system can then be obtained by combining the shaft and multi-disk bolted joint. The resultant governing equations of motion are solved using direct numerical integration. The numerical results obtained from the established model are compared with those of a similar structure in other literature to verify the accuracy of the method used in this study. Then, the dynamic behavior of the rotor system and the mechanical properties of the multi-disk bolted joint under a rubbing fault are presented. Finally, the chaotic response with the rub-impact force acting on different positions of the multi-disk bolted joint is investigated through numerical simulations.

Feature extraction of rotor-stator rubbing faults based on harmonic fusion vector bispectrum, ITD and Hjorth parameters

To solve the difficulty in extracting the characteristics of rotor–stator rubbing faults, the paper has proposed the combined method of Complexity parameter, the harmonic fusion vector bispectrum (HFVB), and intrinsic time-scale decomposition (ITD). First, to fully embody the characteristic information of fault, the HFVB is used to blend the information of signals collected from sensors installed in different positions. Second, taking in mind that the ITD algorithm can embody the effective separation of nonstationary and nonlinear signals, the ITD algorithm makes the separation of blended signals. Third, regarding the important influence of signal complexity on fault characteristic extraction, the complexity parameter of Hjorth parameters can provide very great embodiment of signal complexity. Complexity parameter of Hjorth parameters is introduced as a characteristic parameter index to make a option of proper rotation component (PRC) which can show the characteristics of rubbing fault better. Fourth, signals are reconstructed based on chosen signal components. Meanwhile, to reduce the influence of noise, reconstructed signals are denoised accordingly. Finally, implement the characteristic extraction and fault identification of rubbing faults according to the square demodulation spectrum (SDF) of denoised signals. The result indicates that the harmonic fusion vector bispectrum method can embody the effective blending of fault information; the complexity parameter in Hjorth parameter can serve as the index parameter for option of sensitive characteristic components of rubbing faults. Based on the proposed method, in the square demodulation spectrum of reconstructed signals, it can effectively and precisely provide the characteristics of rotor–stator rubbing fault and successfully identify a fault type.8714542030

Dynamic Response Analysis of Dual-Rotor System with Rubbing Fault by Dimension Reduction Incremental Harmonic Balance Method

The dimension reduction incremental harmonic balance (DRIHB) method is developed to study the dynamic behavior of dual-rotor system with multi-frequency excitations and nonlinear rubbing faults. On the basis of consideration of an aero-engine, a dynamic model of rotor system is built and the piecewise-nonlinear model of rubbing force is used to investigate the nonlinear behavior of system. Considering the features of multi-frequency excitation, high dimension and strong nonlinearity of dual-rotor system, the dimension reduction approach combined with the incremental harmonic balance (IHB) method is derived for theoretically studying the dynamic response of system with nonlinear rubbing fault. The accuracy and efficiency of the method are proved through comparison with the numerical simulation result solved by the Newmark-[Formula: see text] method and the IHB method. Then, the influences of rubbing stiffness, contact gap, rotational speed and speed ratio on dynamic response are studied and discussed. It is shown that the dual-rotor system with nonlinear rubbing fault will cause the system to generate rich combination frequency components in addition to excitation frequency. All the works indicate that the DRIHB method is an effective tool for studying the nonlinear behavior of dual-rotor systems with multi-frequency excitation, high dimensions and strong nonlinearities.

A research on rubbing feature extraction based on information fusion and signal decomposition algorithm

To effectively identify the rotor–stator rubbing fault, the paper has brought forward a method combining principal component analysis (PCA), intrinsic time-scale decomposition (ITD), and information entropy (IE). Firstly, in considering that the characteristic information of faults extracted from the information collected by single sensor is not complete or comprehensive, the approach blends the vibration signals collected from 4 different positions at the same moment based on PCA algorithm; secondly, regarding that ITD algorithm can effectively avoid the problems of poor adaptivity and end effect, blended signals are broken down based on ITD algorithm; thirdly, calculate the IE of self-correlation function of each PRC based on the fact that the smaller IE is, the less confusion system has and the easier it is to extract fault characteristics, and treat the self-correlation function of PRC related with the minimum IE as optimal component to represent fault characteristics; fourthly, characteristic extraction of rotor–stator rubbing fault and identification are done on the basis of the frequency spectrum of optimal component. To prove the availability of method, vibration signals are subjected to validation and analysis, which are collected from different rotation speeds, casing thicknesses, rubbing positions, and types. The result indicates that the proposed PCA–ITD–IE can equally and effectively extract the characteristics of rotor–stator rubbing faults of aero-engine involved in various conditions.

Intelligent rubbing fault identification using multivariate signals and a multivariate one-dimensional convolutional neural network

A rub-impact fault is recognized as a complex, non-stationary, and non-linear type of mechanical fault that frequently occurs in turbines. Extracting features for diagnosing rubbing faults at their early stages requires complex and computationally expensive signal processing approaches that are not always suitable for industrial applications. Furthermore, most of the known techniques experience challenges when applied to multivariate signals. In this paper, an intelligent approach that utilizes multivariate signals and a multivariate one-dimensional convolutional neural network is proposed for diagnosing rubbing faults of various intensities. Specifically, the vibration signals are first collected using multiple sources and then they are resampled into windows with overlap. Next, the envelope power spectra are extracted from the resampled signals to create patterns that are used as the inputs for the multivariate one-dimensional convolutional neural network and to reduce the signal dimensionality to speed up the operation of the intelligent framework. The pairs of convolutional and subsampling layers are used to extract the discriminative local features from the signals collected using multiple sources. These features are used to make a decision about the state of the system in the output layer of the proposed convolutional neural network. The proposed methodology is tested on two different rubbing fault datasets. The experimental results demonstrate that the proposed intelligent fault diagnosis framework is capable of differentiating rubbing faults of various intensities with high classification accuracy.

Identifying rotor-stator rubbing positions based on intrinsic time scale decomposition-hjorth-cepstrum

To accurately locate rotor–stator rubbing faults in aero-engine, a method combining intrinsic time scale decomposition (ITD), Hjorth parameter and cepstrum analysis has been proposed. First, the method works by decomposing vibration signals from casing into proper rotation components (PRCs) based on ITD; second, calculates the autocorrelation function of each rotation component and the complexity parameters of autocorrelation functions; third, chooses PRCs for signal reconstruction according to complexity from Hjorth parameters and reconstructs the signals based on chosen PRCs; at last, considering that with different positions of rubbing, transfer paths of signals collected by the sensors from the same position are different, cepstrum analysis has been made according to reconstructed signals, and the transfer paths characteristics from cepstrum are taken as feature vectors and inputted into support vector machine for identifying the positions of rotor-stator rubbing faults. The results indicate proposed ITD-Hjorth-Cepstrum method can work well in the identification rate of training and test samples as for the identification rate for an unknown sample.

Simulation and Experimental Study on Rotor System Dynamic Analysis with the Blade-Coating Rubbing Faults

In the modern turbo-machinery, reducing the clearance between the blade tip and casing inner face is an effective method to improve the power performance, but the clearance reduction leads to increased risk of blade-casing rubbing. In this paper, a blade-coating rubbing force model which considered the abradable coating scraping is developed to simulate the rotor system dynamic characteristics at blade-casing rubbing faults with abradable coating. An experimental tester is established to simulate the rotor system blade-casing rubbing faults; the AlSi-ployphenyl ester abradable coating is prepared and introduced into the blade-casing experiment to verify the model. After the vibration and force analysis in simulation and experiment, the dynamic characteristics and the influence factors of blade-casing rubbing rotor system are studied.

Research on Identification and Localization of Rotor–Stator Rubbing Faults Based on AF-VMD-KNN

Research on Identification and Localization of Rotor–Stator Rubbing Faults Based on AF-VMD-KNN

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.