Rubbing Fault Research Articles

Dynamic response characteristics of the shaft-blisk-casing system with blade-tip rubbing fault

In this paper, the self-programmed spring-beam-shell hybrid element combined with the Lagrange multiplier method is utilized to establish the finite element model of a fully flexible shaft-blisk-casing system with blade-tip rubbing fault. Particularly, an improved disk-blade interface coupling method is proposed. Besides, the Craig-Bampton method is adopted to establish a reduced system for efficiency promotion. Then the central difference method is applied to solve the rubbing dynamic responses of the reduced system under the effects of different rotating speeds, disk unbalances, and disk positions. Finally, some main conclusions are summarized as follows: (1) In the disk-blade coupling region, three sets of node pairs rather than single node pair are of good accuracy in simulating the dynamic coupling characteristics of the blisk model via the comparisons of the modal results obtained from the experiment and the three-dimensional model in ANSYS; (2) when rubbing with the oval casing, the odd-multiple harmonics in the spectrum of the blisk and the even-multiple harmonics in that of the casing are prominent. Besides, the rubbing region on the casing is usually near the minimum casing radius but changes into the upper- or lower-half zone of the casing under a larger speed.

Experimental analysis of dual-rotor-support-casing system with blade-casing rubbing

Vibration features of inner rotor and casing of a dual-rotor-support-casing (DRSC) system with rubbing existing between blade and casing are analyzed in this work. First, an improved model for analyzing rubbing between blade and casing is presented, in which the kinetic energy of the blade, the deformations of blade and casing are considered. Second, a finite element model of the DRSC system is built as well as the motion equations, where unbalance and time-varying pulse load is considered. Third, natural frequencies and modes, acceleration responses of the casing, and inner rotor of the system with blade-casing rubbing faults are obtained. Finally, the blade-casing rubbing experiments are implemented on the dual-rotor-support-casing test rig, compared with dynamics analysis. The results indicate that (i) the improved rubbing model is more accurate in describing the impact of rubbing between blade and casing; and (ii) the components of impact frequency and the coupling frequencies are prominent when blade-casing rubbing occurs and validated by the experimental results.

A novel intrinsic time–scale decomposition–graph signal processing–based characteristic extraction method for rotor–stator rubbing of aeroengine

Intrinsic time-scale decomposition and graph signal processing are combined to effectively identify a rotor–stator rubbing fault. The vibration signal is decomposed into mutually independent rotational components, and then, the Laplacian energy index is obtained by the graph signal of the autocorrelation function of rotational components, and the signal is reconstructed by an autocorrelation function of each proper rotation (PR) component relative to smaller Laplacian energy index (less complexity). Finally, characteristics are extracted from rotor–stator rubbing faults in an aeroengine according to square demodulation spectrum of a reconstructed signal. To validate the effectiveness of the algorithm, a comparative analysis is made among traditional intrinsic time-scale decomposition algorithm, combination of intrinsic time-scale decomposition and autocorrelation function, and the proposed intrinsic time-scale decomposition–graph signal processing algorithm. Comparative result shows that the proposed intrinsic time-scale decomposition–graph signal processing algorithm is more precise and effective than the traditional intrinsic time-scale decomposition and intrinsic time-scale decomposition and autocorrelation function algorithms in extracting characteristic frequency and frequency multiplication of rotor–stator rubbing faults and can greatly reduce the number of noise components irrelevant to faults.

Nonlinear vibrations of a dual-rotor-bearing-coupling misalignment system with blade-casing rubbing

In order to reveal the nonlinear vibration characteristics of an actual dual-rotor-aero-engine with blade-casing rubbing, a dual-rotor-bearing-coupling misalignment system with blade-casing rubbing are investigated based on numerical simulation and experimental measurement in this paper. A dual-rotor experimental rig is designed and manufactured, that is a simplified structure according a dual-rotor-aero-engine. The dynamic model of the dual- rotor-bearing system of the test rig is established based on the finite element method (FEM) taking into account the coupling misalignment, blade-casing rubbing and the nonlinearities of all of the supporting rolling element bearings. The component mode synthesis (CMS) method is applied to the model order reduction of the high-degrees of freedom (DOFs) dynamic model. The numerical and experimental nonlinear vibration responses of the dual-rotor system are compared with each other at different rotational speeds at different rotational speed ratios. The numerical results are in agreement with the experiment. These results reveal the nonlinear vibration characteristics of the dual-rotor-bearing-coupling misalignment system with local blade-casing rubbing fault.

Diagnosis and elimination of a typical serious rubbing fault of steam turbine

During the operation of a steam turbine in a power plant, the no.3 bearing of the LP rotor suddenly vibrated strongly, which caused the protection action and the turbine tripped. During the maintenance it was found that serious rubbing occurred between the impeller of the LP rotor and diaphragm gland in the LP cylinder. Through inspection and analysis, the location and cause of the rubbing were found, and corresponding treatment was carried out. During the start-up process after maintenance, the vibration of no.1 bearing of HP/IP rotor increased to trip value. In order to eliminate the rubbing of HP/IP rotor, the appropriate warm-up speed was selected and the speed control method was adopted to make the unit start to the working speed and put into normal operation.

Hybrid Rubbing Fault Identification Using a Deep Learning-Based Observation Technique.

A rub-impact fault is a complex, nonstationary, and nonlinear fault that 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. In this article, a hybrid approach that uses a combination of deep learning and control theory algorithms is introduced for diagnosing rubbing faults of various intensities. Specifically, the system is first modeled based on the autoregressive with eXogenous input Laguerre (ARX-Laguerre) technique. In addition, the ARX-Laguerre proportional-integral observer (PIO) is used to increase the estimation accuracy for the vibration signals containing rubbing faults. Finally, a scalable deep neural network is applied to the output signal of the PIO to perform fault diagnosis and overcome potential problems that may appear when applying a linear observation technique to nonlinear signals. The experimental results demonstrate that the proposed hybrid approach improves the fault differentiation capabilities of a relatively simple linear observation technique when it is applied to a complex nonlinear rubbing fault signal and attains high fault classification accuracy. This result means that the proposed framework is highly suitable for applications in actual industrial environments.

Dynamic characteristics analysis of blade-casing rubbing faults with abradable coatings

In this paper, a dynamic model of a “0-2-1” rotor system with rubbing fault between blade and abradable coated casings is developed. The sub-model of rubbing force considers scraping work energy of coating, casing stiffness, and initial clearance between blade tip and casing. A rotor rig is established and samples of abradable coatings are introduced into the rubbing experiment. Vibration characteristics of the rotor system under blade-casing rubbing fault are analyzed. Effects of rotating speed and initial clearance on the rub force and the system vibration are studied. Results show that the vibration of rotor focuses on the fundamental and multiple fundamental frequencies due to the blade-casing rubbing with the abradable coating. The multiple fundamental frequencies, the 2 × and 3 × in particular, are greatly affected by the rotating speed. The fractional harmonic frequencies are strongly influenced by the initial clearance between the blade tip and casing. Besides, the rotating speed and the initial clearance between the blade tip and abradable coating on the casing also affect the amplitude and distribution of the rub force.

A rub fault recognition method based on generative adversarial nets

Faced with the problem of valid data shortage data in practical. There's not enough data to train classifiers which can be satisfied to detect impact-rubbing faults in rotary machine. Bedsides, the large number of noises in working enviroment make the useful signal contaminated. Based on this problem, this paper proposes a rubbing fault recognition method based on a generative adversarial nets named deep convolution generative adversarial nets (DCGAN), which is based on a deep convolutional network frame with generation and discrimination models. The acquired signal is processed by time frequency analysis further to get spectrogram. The DCGAN can perform feature conversion and map it to the potential feature subspace to obtain more robust features. The results illustrate that the proposed method can achieve a much more excellent recognition effect. Thus, the proposed DCGAN model is an effective way to recognize impact-rubbing fault in the practical.

Vibration investigation of rotor system with unbalance and blade-casing rubbing coupling faults

In order to investigate the mechanism of a rotor system with unbalance and blade-casing rubbing coupling faults, the vibration and rub force in a rotor system resulting from unbalance and blade-casing rubbing coupling faults are simulated. At first, a dynamic model of 0-2-1 form rotor is established, and a blade-casing model, which considered blade number, clearance between the blade tip and stator, stiffness and size of the blade, is introduced to the rotor model. The characteristics of unbalance and blade-casing rubbing coupling faults are analyzed by waterfall plot, spectrum, time domain chart of vibration and rub force, and the effects of speed and clearance between the blade tip and stator. Secondly, a rotor system tester is established according to the model structure. The experimental test of rubbing is simulated by adjusting the Feeding Device to control the clearance between the blade and stator. After simulation and experimental results were compared, it was found that fraction frequencies and high integer frequencies were affected by a blade-casing rubbing fault, the clearance and speed had different influence on the dynamic characteristic of rotor system with blade-casing rubbing fault.

The analysis and solution of contact rubbing fault for low pressure rotor of gas-steam combined cycle turbine unit

The contact rubbing fault mechanism for low pressure rotor of gas-steam combined cycle steam turbine unit is analyzed deeply in this paper. It is include that the high start and stop frequency of the gas turbine, the special operation mode of the long-time turning and the high designed turbine turning speed are the main reasons for the axial displacement to the inlet side of the fir-tree root and the contact rubbing fault of the low pressure rotor . At the same time, this paper presents a solution to the problem of contact rubbing fault of low-pressure turbine rotor, and analyzes the dynamic stress and vibration frequency of the new blade after technical improvement. The results show that the stress of root and groove of the new blade and the vibration frequency of the new blade can meet the requirements of safe and stable operation of the unit.

Effects of Bounded Uncertainties on the Dynamic Characteristics of an Overhung Rotor System with Rubbing Fault

This paper investigated the nonlinear vibrations of an uncertain overhung rotor system with rub-impact fault. As the clearance of the rotor and stator is getting smaller, contact between them often occurs at high rotation speeds. Meanwhile, inherent uncertainties in the rubbing can be introduced for a variety of reasons, and they are typically restricted to small-sample variables. It is important to gain a robust understanding of the dynamics of such a system under non-probabilistic uncertainties. A non-intrusive uncertainty quantification scheme, coupled with the Runge-Kutta method, was used to study the effects of the rub-impact related interval uncertainties on the dynamical response individually and simultaneously, including the uncertainties in the contact stiffness, clearance, and friction coefficient. Moreover, the numerical validation of the developed analysis method was verified through comparisons with the scanning approach. The results obtained provide some guidance for investigating the uncertain dynamics of rubbing rotors and diagnosing the rub-impact fault under non-random uncertainty.

An amplitude weak component detection technique based on normalized time-frequency coefficients and multi-synchrosqueezing operation

In the areas of measurement, instrumentation and sensing across science and engineering, the recorded signal is typically manifested as a strong non-stationary characteristic and the amplitude of each component is varied among one another. It is necessary to propose an effective signal processing algorithm that could clearly reflect the fast varying frequency fluctuations of all components. As a recently proposed time-frequency analysis algorithm, multi-synchrosqueezing transform possesses the ability to squeeze the diffused time-frequency (TF) coefficients into the correct instantaneous frequency trajectory position in a TF plane iteratively. However, the amplitude related time-frequency representation result still makes it difficult to detect the fast varying instantaneous frequency for the amplitude weak component contained in a multi-component signal. To address this issue, this study employs a combined normalized time-frequency coefficients and the multi-synchrosqueezing operation technique to make a complete exhibition of the complex TF structure of a multi-component signal with various amplitude weak components. In the proposed method, the amplitude-related TF coefficients are all normalized as a constant value and only the reassigned TF positions after conducting the multi-synchrosqueezing operation multiple times are retained. By exploiting the proposed method on multi-component signals with amplitude weak components, the TF structure for all components can be clearly observed. The effectiveness of the proposed method is evaluated both on a set of simulated data and a set of experimental rubbing fault signals, whereby the implementation results are sufficient to demonstrate the superiority of the proposed method.Highlights1. An amplitude weak component detection technique capable of reflecting the entire TF structure for the measured signal in the real world is proposed in this study.2. The amplitude weak component detection technique is established on the foundation of the multi-synchrosqueezing transform with eliminating the impact of amplitude on the TF structure.3. The TF structure for all components with fast varying frequency fluctuation could be easily observed with the assistance of our proposed method no matter the amplitudes of each component are varied or not.4. The simulation case and real-world rubbing signal analysis result have been sufficient to demonstrate the effectiveness of the proposed method.

Automatic localization of the rotor-stator rubbing fault based on acoustic emission method and higher-order statistics

Localization to the rotor-stator rubbing fault of rotating machinery such as aero-engines has been attracting plenty of attentions in fault diagnosis field. Present study attempts to effectively and accurately localize such rubbing sources based on modal AE method automatically. In order to explore the propagation characteristic of rubbing signals, theoretical analysis and finite element simulation on a stator case are conducted. And the dependence of accuracy of time difference of arrival (TDOA) method on the propagation characteristic is investigated. Based on the analysis result, a higher-order statistics (HOS) algorithm is introduced into acoustic emission (AE) to automatically identify the arrival time of rubbing signals and localize the rubbing source via automatic threshold selection. To verify the effectiveness of the proposed AE method to recognize the rubbing fault, a series of rubbing tests are carried out. It is demonstrated by the experimental results that the accuracy of the proposed method is improved compared with conventional TDOA methods since more than half of the sources localized at the rubbing region can be identified in almost all cases and the identification accuracy is up to 80 % at threshold of 85 % of amplitude.

An Improved Algorithm for Selecting IMF Components in Ensemble Empirical Mode Decomposition for Domain of Rub-Impact Fault Diagnosis

A rubbing fault is a complex non-linear and non-stationary fault that frequently occurs in rotating machinery such as turbines. One of the most frequently applied signal processing techniques for the analysis of rub-impact faults in rotating machines is ensemble empirical mode decomposition (EEMD). Despite the advantages of using EEMD in analyzing non-linear and non-stationary signals, it is crucial to determine which of the extracted intrinsic mode functions (IMFs) carry the most valuable and significant information about the mechanical faults under investigation. In this paper, an improvement in the IMF selection technique is introduced, which is based on the recent ratio of degree-of-presence (DPR) to the Kullback-Leibler divergence (DPR/KLdiv). The number of selected IMFs in the DPR/KLdiv-based technique is subjective with a constant threshold, whereas we apply an adaptive thresholding technique to select the most meaningful IMFs that are relevant to a rubbing fault. The experimental results demonstrate that the proposed enhanced IMF selection algorithm allows for better signal denoising properties than the original technique while preserving significant features evidencing the presence of rubbing faults in rotating machinery.

Fault feature extraction of localised rub-impact fault based on vector-bispectrum and Teager energy operator

Bispectrum analysis is able to suppress the Gaussian noise and analyse quadratic phase coupling in the signals more accurately. However, traditional bispectrum has the problem of losing fault information at low frequency, and may not comprehensively reflect nonlinear information of the fault, which leads to weak diagnostic ability, especially for local rub-impact fault. For this reason, a new feature extraction method called vector-bispectrum energy operator is presented in this paper, which adopts vector-bispectrum based on Teager energy operator and is used to obtain the fault feature of local rubbing rotor. The results of the experiment show that the feature of the local rubbing fault extracted by Teager energy operator based vector-bispectrum is very noticeable, and the fault classification through SVM has a high recognition rate.

Fault feature extraction of localised rub-impact fault based on vector-bispectrum and Teager energy operator

Bispectrum analysis is able to suppress the Gaussian noise and analyse quadratic phase coupling in the signals more accurately. However, traditional bispectrum has the problem of losing fault information at low frequency, and may not comprehensively reflect nonlinear information of the fault, which leads to weak diagnostic ability, especially for local rub-impact fault. For this reason, a new feature extraction method called vector-bispectrum energy operator is presented in this paper, which adopts vector-bispectrum based on Teager energy operator and is used to obtain the fault feature of local rubbing rotor. The results of the experiment show that the feature of the local rubbing fault extracted by Teager energy operator based vector-bispectrum is very noticeable, and the fault classification through SVM has a high recognition rate.

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.

Casing vibration response prediction of dual-rotor-blade-casing system with blade-casing rubbing

Abstract This paper focuses on the dynamic responses of whole aero-engine with blade-casing rubbing. The vibration response of casing is simulated and the dynamic behaviors of casing acceleration under blade-casing rubbing are investigated to diagnose the blade-casing rubbing fault effectively. Firstly, the finite element model of a dual-rotor-blade-casing (DRBC) system with inter-shaft bearing is proposed. The shear deformations and inertias of the rotor and casing are taken into account. The gyroscopic moments of the rotors are evaluated. Secondly, the effects of the blade-casing clearance and the number of blades on the vibration responses of DRBC system with blade-casing rubbing are considered. Finally, the casing acceleration responses of the DRBC system with blade-casing faults are solved numerically, and the influences of some variables, such as the rotating speed ratio, eccentricity of disk and rubbing stiffness, on the dynamic behaviors have been investigated by time waveform of acceleration, frequency spectrum and waterfall. The results indicate that (1) blade-casing rubbing can cause impulsive load to the casing and rotor, and lead to abrupt increase of the vibration amplitude; (2) the obvious periodic impact characteristics are contained in the casing vibration acceleration signals, and the impact frequency equals the product of the rotational frequency and the numbers of blades; (3) the fraction frequency component of rotating speed difference of dual rotors is excited on both sides of impact frequency and its multiple frequency components.

A new characteristic analysis method for aero-engine rotor–stator rubbing

Aero-engine fault diagnosis is often studied according to casing signal owing to the inconvenience of assembly and structural limitations. Satisfactory result by cyclic statistics alone is difficult to obtain because casing signal is weak and complex. Based on this, a cyclostationary theory combined with autocorrelation function and Hilbert transform is applied to extract the characteristics of aero-engine rotor–stator rubbing fault according to the aero-engine structure and rotating features with regard to of single-point rubbing and local rubbing. Signal autocorrelation function is analyzed by cyclic autocorrelation function and Hilbert transform, in order to extract rubbing characteristics based on casing signal of aero-engine and reduce inconsistent frequency in the frequency spectrum between time-delay signal of cyclic frequency slice position and original signal. Meanwhile, consideration is given to the influence of rubbing position and sensor installation position in the extraction of rubbing characteristics. Finally, the Hilbert envelope spectrum is compared and analyzed between normal running and occurrence of the rubbing faults of aero-engines. The result indicates that the different cyclic frequency positions slice signal's Hilbert envelop spectrum of signal autocorrelation function, but not original acceleration signal which has outstanding characteristic frequency for rubbing frequency (product between blade numbers and rotating frequency) and its twice frequency when rubbing fault occurs not only in single rubbing but also in local partial rubbing. Meanwhile, when compared with the original vibration signal slice, inconsistent frequency of the autocorrelation function slice in the Hilbert envelope spectrum is decreased considerably.

A new iterative near-field coherent subspace method for rub-impact fault localization using AE technique

Acoustic emission (AE) localization is an important method to detect defects in bearing of rotatory machine for faults maintenance. However, only the faults near the sensor array can be detected due to severe attenuation in the recorded AE signals. Therefore, we propose a highly reliable new Iterative near-field Coherent subspace method (IN-CSM) for multiple rub-impact faults localization. The proposed approach contains four improved processes: Modal plate wave theory (MPWT) analysis for the multi-modes decomposition and group velocity revision; Discrete wavelet transform (DWT) for the useful narrow band extraction; Near field Multiple signal classification (N-MUSIC) method for the preliminary position estimations; the IN-CSM algorithm for the multiple coherent sources separation and the precise localizations. The simulations based on N-MUSIC and IN-CSM methods were compared by rubbing teston the test rig of rotation machinery. The results indicate that the proposed method can effectively locate multiple coherent rubbing faults at once. Thus, it is an effective analysis tool for rub-impact fault detection.