Inter-shaft Bearing Research Articles

MD-BiMamba: An aero-engine inter-shaft bearing fault diagnosis method based on Mamba with modal decomposition and bidirectional features fusion strategy

Inter-shaft bearing fault diagnosis can greatly save maintenance costs and guarantee the normal operation of aero-engines. However, existing methods are limited in their ability to handle sensor signals with high dimensional and complex noise. To tackle the above problems, we propose a Mamba network structure with Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) and bidirectional feature fusion for aero-engine inter-shaft bearing fault diagnosis, called MD-BiMamba. Firstly, we utilize the CEEMDAN technique to decompose the sensor signals of inter-shaft bearings and extract the intrinsic modal function by improving the noise addition method and decomposition strategy. Then, bidirectional Mamba is designed to extract the bidirectional long-range correlation of the sequence to achieve global feature extraction and fast detection of fault types with linear complexity. Moreover, an adaptive attention fusion method is proposed to achieve bidirectional feature fusion. Finally, we use the label smoothing regularization strategy to optimize the cross-entropy loss and enhance the generalization performance. Experimental results on real inter-shaft bearing datasets and noisy datasets show that the proposed method achieves 99.88 % and 95.81 % accuracy in the standard dataset and −10 dB noise environment, respectively, which is superior to other remarkable methods, in addition to achieving lower model complexity.

HLSM-MIPV Algorithm of unbalance vibration suppression of dual-rotor in contra-rotating propfan

The inner and outer rotors of the contra-rotating propfan dual-rotor system, utilizing dual intershaft bearings, exhibit anisotropic support characteristics, whereas the vibration of the dual-rotor system is cross-coupled. This combination makes the identification of unbalanced responses and the efficiency of dynamic balancing challenging. To address this issue, this paper proposes a method for the dynamic balancing of the contra-rotating dual-rotor based on Harmonic Least Squares Method and Modified Initial Phase Vector (HLSM-MIPV). Firstly, a test bench for the contra-rotating dual-rotor system is constructed using two Micro-Electro-Mechanical Systems (MEMS) sensors. Secondly, unbalanced vibration vectors of the dual-rotor are identified using Harmonic Least Squares Method (HLSM). Thirdly, the Harmonic Component Method with the Modified Initial Phase Vector (MIPV-HCM) is introduced to balance the force and couple unbalance under anisotropic stiffness conditions. Finally, dynamic balancing tests on the test bench demonstrate that the MIPV-HCM method achieves an additional vibration reduction of 4 %–17 % compared to the traditional HCM.

Composite failure analysis of an aero-engine inter-shaft bearing inner ring

The inter-shaft bearing is a critical component in dual rotors aero-engine. Due to the complex and severe loads caused by the interactive excitation of HP and LP rotors during operation, the inter-shaft bearing is prone to damage accumulation and failure. Focusing on a typical failure of inter-shaft bearing inner ring fragmentation and cannot be spliced together completely in high thrust-weight ratio turbofan engine, this paper conducted morphological investigation, fractographic analysis, vibration signal processing, finite element numerical simulation, and fully studied the failure mechanism of this failure.The results indicated that: there exists an uncoordinated resonance speed of the HP rotor in close proximity to the operating speed. This puts the rotor in non-synchronous procession state, accompanied by the uncoordinated angular displacement of the inner and outer rings, which resulting in a lager rolling dynamic load in bearing inner ring. This further leads to high tangential impact load at the root fillet of the anti-rotation pin, causing significant stress concentration, and eventually leads to the generation of initial cracks. These cracks persist and propagate into fatigue oblique fracture over time. After oblique fracture, the modal frequencies of the inner ring become more dispersed. Under the rolling dynamic load (traveling wave load), nodal diameter vibration occurs, causing high stress vibration fatigue damage, and ultimately leading to multiple-point simultaneous fragmentation.The investigation suggests that reducing the stress levels at the root fillet of the anti-rotation pin of the inner ring is an effective approach to prevent bearing failure. This can be achieved through two methods: one is optimizing the rotor structure to decrease the rolling dynamic load on the inner ring, the other is eliminating the anti-rotation pin and appropriately reducing the tightening torque of the compression nut and the interference between the bearing inner ring and the HP turbine rear journal.

Prediction and analysis of paroxysmal impulse vibration in aero-engine inter-shaft bearings induced by localized faults in the outer ring

Prediction and analysis of paroxysmal impulse vibration in aero-engine inter-shaft bearings induced by localized faults in the outer ring

Analysis of Nonlinear Vibration Characteristics and Whirl Behavior of Dual-Rotor Systems with Inter-Shaft Rub Impact

Previous studies on rub-impact faults have mainly focused on the rub-impact between rotors and stators, with less research on inter-rotor rub impact. The impact of inter-rotor rub impact on rotor nonlinear vibration is particularly significant. This study investigates the effects of inter-shaft rub impact on the vibration characteristics and whirl behavior of dual-rotor systems. Initially, a dual-rotor model with inter-shaft bearings is established using the finite element method, and inter-shaft rub-impact forces are derived based on contact mechanics. Next, the system response is solved using the Newmark method. Vibration characteristics are analyzed through Campbell diagrams, 3D waterfall plots, time-frequency domain plots, and steady-state rub-impact force plots. Finally, the influence of inter-shaft rub impact on the whirl behavior of the dual-rotor system is studied based on the theory of full-spectrum analysis. The study concludes that inter-shaft rub-impact faults shift the system’s resonance points backward, increase harmonic and combination frequency components, and significantly affect the system response under dual-rotor co-rotation. Excessive friction can lead to self-excited vibrations and sudden amplitude increases, particularly in the LP rotor frequency. Additionally, inter-shaft rub impact primarily affects the whirl behavior of the LP-compressor disk1, showing multiple cycles of forward and backward whirl alternation during acceleration due to combined unbalanced and rub-impact excitations.

Research on inter-shaft bearing fault diagnosis method based on STFT-CNN modeling

Inter-shaft bearings are an essential component of aircraft engines, and their operational status determines the safety of aircraft engine operation. Therefore, to improve the accuracy of fault type prediction and enrich the feature information in vibration signals of aircraft engine inter-shaft bearings, this paper proposes an STFT-CNN model based on the AlexNet architecture, extending its application to the research of aircraft engine inter-shaft bearing fault diagnosis. This approach addresses the common reliance on personnel experience for fault type diagnosis in traditional aircraft engine inter-shaft bearing fault diagnosis. Firstly, real vibration fault signals from inter-shaft bearings are collected through experiments to enrich feature information in non-stationary signals using STFT time-frequency methods. Secondly, utilizing the high interpretability of the STFT-CNN model, fault feature data from inter-shaft bearings under various operating conditions are extracted to refine our understanding of fault feature information. Finally, leveraging the robustness of the STFT-CNN model, fault types are classified and predicted. The training process involves comparative analysis using different pooling algorithms, time-frequency analysis methods, and various deep learning network models. The results demonstrate that the STFT-CNN model, employing the maximum pooling algorithm, outperforms other models in predicting inter-shaft bearing faults, achieving an average fault prediction accuracy of 98.8% .

Backward whirling behaviors of a twin-spool rotor system with coupling inter-shaft and rotor-stator rubbings

The aim of this paper is to investigate the backward whirling behaviors of an aero-engine twin-spool rotor system with coupling rubbings. Firstly, considering the effects of the inter-shaft and rotor-stator rubbings, the dynamic model for a twin-spool rotor system without inter-shaft bearing is developed by means of finite element method. Subsequently, using three-dimensional full spectrum and rotor orbits, the backward whirling behaviors of twin-spool rotor system are illustrated, and the effects of rotational direction and speed ratio on the whirling direction of the rotor are discussed as well. The results reveal that backward inter-shaft and rotor-stator frictions are the physical reasons of backward whirl in the rubbing rotor. For the twin-spool rotor system with inter-shaft rubbing, when the speed ratio is positive, the high-pressure rotor can strengthen the rotation of the low-pressure rotor through the inter-shaft rubbing point, and the low-pressure rotor maintains in forward whirl. In contrast, when the speed ratio is negative, the larger inter-shaft friction may induce backward whirl for the low-pressure rotor. Regardless of whether the speed ratio is positive or negative, the rotor-stator rubbing always contributes to promote the backward whirl of the rotor. As the speed ratio goes up, the initial speed of the backward whirl drops and the opposite is also true. These findings contribute to understanding the mechanism of backward whirling behaviors for the rubbing twin-spool rotor system.

Paroxysmal impulse vibration analysis of an aero-engine dual-rotor system with a defective inner ring for the inter-shaft bearing

Inter-shaft bearings play a central role in connecting high-pressure (HP) and low-pressure (LP) rotors within aero-engines. Local defects in these bearings can lead to two distinct and complex vibration modes—paroxysmal or continuous impulse vibrations, which arise from the unique installation positions. This study offers a comprehensive exploration of the dynamic phenomena, the underlying physical mechanism, and the analytical conditions for the occurrence of paroxysmal impulse vibrations. The local defects of the inner ring are found to induce paroxysmal impulse vibrations when specific rotational speed ratios between HP and LP rotors are achieved. The dynamic differences and connections between paroxysmal and continuous impulse vibrations are contrasted. Three analytic and explicit prediction formulas are derived, enabling the direct calculation of the operating conditions for paroxysmal impulse vibrations. A summarized prediction flow for paroxysmal impulse vibrations is established. In addition, the proposed prediction formulas and flow allow for the prediction of the precise frequency components of paroxysmal impulse vibrations. In the validation of the simulation results, three experimental cases involving inter-shaft bearings with inner ring defects are conducted, confirming the existence of paroxysmal dynamic phenomena and validating the effectiveness of the proposed prediction formulas and prediction flow for paroxysmal impulse vibrations. Hence, this study offers a novel approach to understanding inter-bearing vibration fault mechanisms.

Simulation method and spectrum modulation characteristic analysis of typical fault signals of inter-shaft bearing

In order to study the frequency spectrum characteristics of the vibration signal of the inter-shaft bearing defect fault in the aero-engine dual-rotor system, a vibration signal mathematical model is established based on the fault characteristic frequency of the inner and outer ring defects of the inter-shaft bearing, and the mutual modulation law of the signals during transmission is analyzed. A test bench for signal transmission path analysis is built to verify the calculation results. The results indicate that the fault signal of the inter-shaft bearing defect significantly attenuates during transmission, and the characteristic frequency of the inter-shaft bearing fault is modulated with the rotor rotation frequency. There are corresponding characteristic frequencies and modulation frequency components in the envelope spectrum of the inter-shaft bearing. The error between the experimental and simulation results is less than 1%, which verifies the accuracy of the simulation calculation results. After being transmitted to the rotor through the inter-shaft bearing, the rotor frequency includes the modulation frequency of bearing varying compliance frequency and rotation frequency, as well as the fault characteristic frequency of the inter-shaft bearing.

Nonlinear Dynamic Analysis on Dual‐Rotor‐Bearing‐Casing System for Marine Gas Turbine

Taking the marine gas turbine as a research background, a dual‐rotor‐bearing‐casing system model was established considering the bearing nonlinearities and unbalanced excitation. Based on Lagrange’s equation of motion and rotor dynamics theory, the effects of key parameters such as radial clearance of intershaft bearing, rotor mass eccentricity, and rotational speed on the nonlinear characteristics of the system are investigated. The results indicate that the typical parameters have a significant effect on the system’s nonlinearities. To alleviate the vibration jump phenomenon, the radial clearance should be reduced to improve the coupling between the high‐ and low‐pressure rotors. Reducing the mass eccentricity can effectively degrade the resonance peaks, but it will highlight the hard resonance characteristics. The work process should pass through the resonant‐speed regions and the low‐speed regions of start‐stop phase as soon as possible. The research findings contribute to understanding the nonlinear dynamic characteristics of dual‐rotor systems, providing a theoretical basis for their stable operation and the optimal design of working speeds.

A comprehensive study on natural characteristics and dynamic responses of a dual-rotor system with inter-shaft bearing under non-random uncertainty

Aeroengines are usually designed with a dual-rotor configuration for the rotating part. A dual-rotor system has coupling characteristics introduced by an inter-shaft bearing, and the rotating direction of the rotors has critical influences on the performance. It becomes more complicated when the inevitable uncertainties of the dual-frequency excited dynamical system are considered. This paper delivers a comprehensive study of the natural characteristics and dynamic responses of a dual-rotor system with an inter-shaft bearing considering the non-random parametric uncertainties under co- and counter-rotating conditions. To this end, the finite element modeling and the deterministic solutions of a dual-rotor system are established. Then, the polynomial surrogate function is constructed for the desired natural characteristics and dynamic responses under non-random uncertainty. The polar interpolation technique is implemented to compute uncertain shaft orbits, overcoming difficulties in the traditional frequency-sense measure. Intensive case studies for different interval uncertain parameters are carried out and the results are comparatively discussed. It is found that the mass unbalance uncertainties only affect the respective modes excited by the rotor where the unbalance is located. The shaft stiffness has global uncertainty effects on the Campbell diagram, mode shapes, time history, shaft orbit and responses. Uncertainties in the inter-shaft bearing stiffness and speed ratio generally influence higher-order modes. The results of the present work gain insights into the modal characteristics and dynamical behaviors of the dual-rotor system under complex parametric uncertainties.

Inter-shaft Bearing Fault Diagnosis Based on Aero-engine System: A Benchmarking Dataset Study

In this paper, the aero-engine test with inter-shaft bearing fault is carried out, and a dataset is proposed for the first time based on the vibration signal of rotors and casings. First, a test rig based on a real aero-engine is established, driven by motors and equipped with a lubricating system. Then, the aero-engine is disassembled and assembled following the specification process, and the inter-shaft bearing with artificial fault is replaced. Next, the aero-engine test is conducted at 28 groups of high and low pressure speeds. Six measuring points are arranged, including two displacement sensors to test the displacement vibration signals of the low pressure rotor and four acceleration sensors to test the acceleration vibration signals of the casing. The test results are integrated into an inter-shaft bearing fault dataset. Finally, based on the dataset in this paper, frequency spectrum, envelope spectrum, CNN, LSTM and TST are used for fault diagnosis, and the results are compared with those of CWRU and XJTU datasets. The results show that the characteristic fault frequency cannot be found directly in the spectrum and envelope spectrum corresponding to this paper's dataset but in CWRU and XJTU datasets. Using CNN, LSTM and TST for fault diagnosis of the dataset in this paper, the accuracy is 83.13%, 85.41% and 71.07%, respectively, much lower than the diagnosis results of CWRU and XJTU datasets. It can be seen that the dataset in this paper is closer to the actual fault diagnosis situation and is a more challenging dataset. This dataset provides a new benchmark for the validation of fault diagnosis methods. Mendeley data: https://github.com/HouLeiHIT/HIT-dataset.

Nonlinear thermo-mechanic coupling effect of a dual-rotor system with an intershaft bearing

Nonlinear thermo-mechanic coupling effect of a dual-rotor system with an intershaft bearing

Failure analysis of an aero-engine inter-shaft bearing due to clearance between the outer ring and its housing

The inter-shaft bearing is a critical but vulnerable component of dual rotors, because of the severe operational conditions and loads. This paper investigates the failure mechanism of a fractured inter-shaft bearing belonging to a high thrust-weight ratio turbofan engine. Fractographic and microscopic analyses of the fracture surfaces were conducted, followed by vibration signal processing. Finite element analyses of the outer ring were also performed considering the centrifugal, thermal, and roller-raceway loads. What’s more, using the linear elastic fracture mechanics theory, the crack growth path simulation was obtained, whose result showed good agreement with the real fracture morphologies. The results indicated that due to the clearance between the outer ring and its housing during the operation, the anti-rotation tabs of the outer ring were subjected to non-uniform load, thus several tabs might suffer large stress concentrations at the root fillets, which could lead to the crack initiation. During the following operation of the aero-engine, the crack propagated through the outer ring and cause the fatigue fracture of tabs. The investigation provided herein suggests that the outer ring and its housing should be redesigned to eliminate the clearance during the operation, an outer ring formed integrally with the bearing housing flange is one of the failure preventions of this failure mode.

Dynamic modeling and simulation analysis of inter-shaft bearing fault of a dual-rotor system

In order to study the vibration characteristics of inter-shaft bearing failures of a dual-rotor system, an eight-degree-of-freedom dynamic model of dual-rotor system containing inter-shaft bearings is established. The Newmark-β method is used to solve the proposed model equations. The dynamic characteristics of the rotor system when the inner ring and outer ring of the inter-shaft bearing has single-point failures or composite failures are analyzed. The comparison results show that the fault frequency distribution pattern in the envelope spectrum of the dynamic simulation results is consistent with that of the test results, which proves the effectiveness of the proposed dynamic model. It is found that when the inter-shaft bearing fails, a combination of rotor rotation frequency, multi-frequency, and fault frequency modulation frequency occurs in the fault characteristic frequency of the dual-rotor system. In addition to the speed-synchronized vibration components caused by the eccentricity, the rotor vibration signal is usually accompanied by a high-order harmonic vibration signal.

Dynamic characteristics of a dual-rotor system with parallel non-concentricity caused by inter-shaft bearing positioning deviation

The machining deviation of the positioning hole of the inter-shaft bearing can cause the fault of the non-concentricity of the dual-rotor system. Aiming at the above problem, a type of parallel non-concentricity is defined, the phase angle and the offset of which are utilized to modify the contact force model of the inter-shaft bearing. The results obtained by the Newmark-β method show that the non-concentricity phase angle and the non-concentricity offset will change the amplitude when the dual-rotor system passes the first critical speed. It is observed that there are 2X and 3X frequencies of the rotational speeds of high- and low-pressure rotors and several combination frequencies of the two rotational speeds, in which the subtraction frequency of high- and low-pressure rotors is dominant. With the non-concentricity phase angle changes, the shape of the orbit and the envelope curve of the orbit of high- and low-pressure rotors will shift. The quantitative correspondence between the polar angle difference and the non-concentricity phase angles is discovered, which can be used to diagnose the fault of the non-concentricity of the dual-rotor system.

Combination resonance and primary resonance characteristics of a dual-rotor system under the condition of the synchronous impact of the inter-shaft bearing

The internal structure of many aero-engines is designed with a dual-rotor system. Up to now, there have been few studies on the influence of aerodynamic excitation on the dual-rotor system. The phenomenon of synchronous impact may occur when the frequency of the aerodynamic excitation force of the fan blade is close to the characteristic frequency of the inter-shaft bearing. This paper investigates the dynamic characteristics of a dual-rotor system under the condition of synchronous impact. The system's motion equations are formulated considering the complex nonlinearities of the inter-shaft bearing, such as Hertz contact force of 10/9 exponential function, clearance, and periodic varying compliance. In addition, the inter-shaft bearing with a local defect is considered. The fan blade’s aerodynamic excitation force is modeled by synthesizing multiple harmonic excitation forces, the amplitudes of which are obtained by the Fourier series expansion. Numerical simulations are employed to get the dynamic responses of the system. The results show that the dynamic characteristic of the dual-rotor system at the primary resonance caused by the high-pressure (H.P.) rotor is not changed by the aerodynamic excitation force, while the primary resonance caused by the low-pressure (L.P.) rotor increases significantly. However, three aerodynamic resonances of the amplitude-frequency response of the dual-rotor system are emerging in the low-frequency region (124, 146 and 186 rad/s). When the synchronous impact phenomenon occurs, the amplitude of the three resonance peaks will increase twice compared to the original status, leading to a doubled increase in the dynamic load of the inter-shaft bearing. The characteristics of the dual-rotor system affected by the parameters such as initial phase difference of local defect, rotor eccentricity of system, clearance of inter-shaft bearing, and the stiffness and damping of supports are discussed in detail. The results obtained provide a deep insight into the mechanism of synchronous impact.

Combination resonances of a dual-rotor system with inter-shaft bearing

Combination resonances of a dual-rotor system with inter-shaft bearing

Vibration Behavior of Dual-Rotor Caused by Maneuver Load and Intershaft Bearing Defect

This paper concentrates on the vibration amplitude modulation and frequency modulation behavior of a dual-rotor system induced by the maneuver load and defective intershaft bearing. The motion equations of a dual-rotor system are presented by considering the intershaft bearing force with a local defect of the outer raceway and the maneuver load of a barrel-roll flight. The fourth-order Runge–Kutta method is employed to study the vibration responses of the dual-rotor system, which are reflected by the time history curves, the bearing contact force curves, and the Hilbert envelope spectra. It is shown that the rotor responses display impulse vibrations due to the defective intershaft bearing; and the corresponding Hilbert envelope spectra contain defect characteristic frequencies, multiple defect frequencies, side frequencies, and modulation frequencies. The results reveal the frequency modulation behavior of the impulse vibrations induced by the rotating speed ratio and the amplitude modulation behavior influenced by the maneuver load, the bearing defect span, and the rotating speed. Finally, defective intershaft bearing experiments under maneuvering flight are conducted, confirming the availability of the numerical vibration amplitude modulation and frequency modulation behavior. This analysis provides a theoretical foundation for bearing state detection during flight maneuvers.

Research on compound faults identification of aeroengine inter-shaft bearing based on CCF–Complexity–VMD–SVD

Inter-shaft bearing is an important component of dual-rotor aeroengine and it is difficult to extract fault characteristics and identify a fault type. Therefore, the paper has proposed a method (CCF–Complexity–VMD–SVD) combining information fusion, Complexity parameter of Hjorth parameters, variational mode decomposition (VMD), and singular value decomposition (SVD). Firstly, to fully embody fault characteristic information, the method has established the cross-correlation function (CCF) of homologous acceleration information from the casing of one of the aeroengines (acceleration signals collected from the same section at the same moment in orthogonal directions) to blend homologous information, reinforce fault characteristic components, and lessen the influence of noise. Secondly, considering the great influence of signal complexity on the extraction of fault characteristics and the Complexity parameter of Hjorth parameters can express the complexity of signals better, the Complexity parameter of Hjorth parameters is placed into the fault characteristic extraction of inter-shaft bearing. The Complexity parameter is applied to optimize the number of layers and central frequency of VMD. Thirdly, signals are denoised through SVD to further lessen the influence of noise on characteristic extraction. Finally, frequency spectrum (FS) of signal denoised is used to make characteristic extraction and fault identification of compound faults of inter-shaft bearing. The result of comparative analysis with other methods has further illustrated the proposed method CCF–Complexity–VMD–SVD that can actualize the effective characteristic extraction of compound faults and precise identification in the early stage of fault based on vibration signals from casing of aeroengine. The performance of engineering appliance of the proposed method has been further verified through fault analysis of disassembly for the aeroengine.