Experimental diagnosis of multiple faults on a rotor-stator system by fast Fourier transform and wavelet scalogram

This paper presents the recent application of the scalogram of Continuous Wavelet Transform (CWT) as a vibration monitoring and signal processing tool for a rotor dynamic response under parametric excitation. The experimental test data of coupled lateral-torsional vibrations of a rotor-stator system with transverse crack was obtained through a data acquisition set-up interfaced with Rotor-Kit-4 (RK-4). Analysis was executed on rotor deflection, orbit, frequency and time-frequency spectrum of the RK-4 experimental data. The scalograms of CWT were used experimentally to represent the aperiodic occurrence of rub between the rotor-stator and crack features. Variation in 3-D scalogram peaks in the presence of rub and crack were unique and were used to distinguish quasi-periodic motion from other types of motion. An unbalanced cracked rotor gave a higher frequency amplitude response compared to an unbalanced rotor with rub under the same conditions. Irregularities in orbit orientation near sub-harmonic resonances were observed in the test data. Multiple rebounds inside the orbit loop were unique rub indicators. Conspicuous horizontal components of the higher harmonics were observed near the critical speed when a crack existed. CWT established inherent feature patterns that discriminated unbalance, rub and a crack

Mathematical Validation of Experimentally Optimised Parameters Used in a Vibration-Based Machine-Learning Model for Fault Diagnosis in Rotating Machines

Mathematical models have been widely used in the study of rotating machines. Their application in dynamics has eased further research since they can avoid time-consuming and exorbitant experimental processes to simulate different faults. The earlier vibration-based machine-learning (VML) model for fault diagnosis in rotating machines was developed by optimising the vibration-based parameters from experimental data on a rig. Therefore, a mathematical model based on the finite-element (FE) method is created for the experimental rig, to simulate several rotor-related faults. The generated vibration responses in the FE model are then used to validate the earlier developed fault diagnosis model and the optimised parameters. The obtained results suggest the correctness of the selected parameters to characterise the dynamics of the machine to identify faults. These promising results provide the possibility of implementing the VML model in real industrial systems

Crack detection in a rotating shaft using artificial neural networks and PSD characterisation

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Mathematical Validation of Experimentally Optimised Parameters Used in a Vibration-Based Machine-Learning Model for Fault Diagnosis in Rotating Machines

From MDPI via Jisc Publications RouterHistory: accepted 2021-08-03, pub-electronic 2021-08-07Publication status: PublishedMathematical models have been widely used in the study of rotating machines. Their application in dynamics has eased further research since they can avoid time-consuming and exorbitant experimental processes to simulate different faults. The earlier vibration-based machine-learning (VML) model for fault diagnosis in rotating machines was developed by optimising the vibration-based parameters from experimental data on a rig. Therefore, a mathematical model based on the finite-element (FE) method is created for the experimental rig, to simulate several rotor-related faults. The generated vibration responses in the FE model are then used to validate the earlier developed fault diagnosis model and the optimised parameters. The obtained results suggest the correctness of the selected parameters to characterise the dynamics of the machine to identify faults. These promising results provide the possibility of implementing the VML model in real industrial systems

Health Monitoring of Cracked Rotor Systems Using External Excitation Techniques

Cracked rotors present a significant safety and loss hazard in nearly every application of modern turbomachinery. This thesis focuses on the health monitoring, modeling, and analysis of machines with transverse breathing cracks, which open and close due to the self-weight of the rotor. After considering the modeling of cracked rotors, the thesis investigates an active structural health monitoring approach, focusing on the application of an active magnetic actuator to apply a specially designed external force excitation to the rotating shaft. Extensive experimental data has been collected and analyzed utilizing advanced diagnostic techniques. The presented results demonstrate that the use of a magnetic force actuator to apply external excitation has potential in the diagnostics of cracked rotors. The observed unique crack signatures demonstrate the ability of the method for early diagnosis of transverse rotor crack

Health Monitoring of Cracked Rotor Systems Using External Excitation Techniques

Cracked rotors present a significant safety and loss hazard in nearly every application of modern turbomachinery. This thesis focuses on the health monitoring, modeling, and analysis of machines with transverse breathing cracks, which open and close due to the self-weight of the rotor. After considering the modeling of cracked rotors, the thesis investigates an active structural health monitoring approach, focusing on the application of an active magnetic actuator to apply a specially designed external force excitation to the rotating shaft. Extensive experimental data has been collected and analyzed utilizing advanced diagnostic techniques. The presented results demonstrate that the use of a magnetic force actuator to apply external excitation has potential in the diagnostics of cracked rotors. The observed unique crack signatures demonstrate the ability of the method for early diagnosis of transverse rotor crack

Model Development and Stability Analysis for a Turbocharger Rotor System under Multi-Field Coupled Forces

Automotive turbochargers have been widely applied in vehicles in order to increase the power output of internal combustion engines by increasing the air to fuel ratio entering the piston cylinders. Turbochargers use the exhaust flow to spin a turbine at speeds of up to 140,000 r/min. Under such extreme working conditions, even a weak vibration can lead to the bearing failure and the whole turbocharger destroyed. In order to guarantee a safe operation, it is necessary to carry out a theoretical research on the dynamics performance of turbochargers. Therefore, the primary objective of this research is to develop a dynamics model for the turbocharger rotor system under multi-field coupled forces and then to study the dynamic characteristics and the stability of its rotor system according to the simulation and experimental results. A turbocharger is a special kind of rotating machinery because of the following aspects: Firstly, the turbocharger rotor system is supported by floating ring bearings. The impact of nonlinear multi-field coupled forces must be considered. Secondly, the turbocharger rotor system is a multi-span rotor bearing system that makes the modeling and simulation more complicated. Thirdly, the working speed range of the turbocharger covers multiple orders of critical speeds. This flexible rotor system cannot be studied using the conventional theory of rigid rotors. In this thesis, the lubrication system of a turbocharger is initially investigated. The analytical expressions of the hydrodynamic pressure distribution in the floating ring bearing are derived using the infinitely long bearing theory, taking into account the oil inlet pressure and the cavitation area. The influences of external loads and oil inlet pressure on the oil flow rate into the inner clearance are analytically investigated, while considering the effect of the rotation of the ring. A finite element model is then developed for the turbocharger rotor system. In this model, the excitation forces considered include rotor imbalance, hydrodynamic forces, lubricant feed pressure and the dead weight. The dimensionless form of Capone hydrodynamic force model is extended into the floating ring bearing. Following model development, modal analysis is carried out on both a free rotor system and a turbocharger rotor system. The effects of the structural parameters and working conditions, such as the rotor imbalance, lubricant viscosity, bearing clearances and lubricant feed pressure, on the stability of the turbocharger rotor system are studied. A turbocharger test rig is then designed and developed to monitor the turbocharger shaft motion. The experimental data agree well with the simulation results from the theoretical model. The primary contribution of the current research can be categorized into the following aspects: Firstly, the analytical expressions of the hydrodynamic pressure distribution have been solved. The equilibrium positions of the journal and ring have been deduced under different external loads and lubricant feed pressure. The relationship between the oil flow rate and the rotational velocity of the shaft has been obtained. Secondly, Capone hydrodynamic force model is introduced and extended to simulate the dynamic performance of the floating ring bearing. The analytical expression of the hydrodynamic forces of double oil films have been derived based on the dimensionless form of the Reynolds Equations. Thirdly, the motion of the turbocharger shaft is simulated within a speed range of 0 to 8,000 rad/s. The influences of structural parameters and working conditions on the stability of the turbocharger rotor system are clearly understood. It should be noted that the developed model still needs to be validated when turbocharger is operated at a relatively high speed, although it agrees well with experimental results within the speed range of 0 to 2,000 rad/s

Multi-fault classification of rotor systems based on phase feature of axis trajectory in noisy environments

As it is difficult to distinguish multiple rotor faults with similar dynamic phenomena in noisy environments, a multi-fault classification method is proposed by combining the extracted trajectory phase feature, a parameter-optimized variational mode decomposition (VMD) method and a light gradient boosting machine (LightGBM) model. The trajectory phase feature is extracted from an axis trajectory by fusing the frequency, amplitude, and phase information related to rotor motion and can comprehensively describe the dynamic characteristics induced by different rotor faults. First, the vibration displacement signals in two orthogonal directions are collected to construct the axis trajectories with 12 rotor states including healthy, unbalance, misalignment, single crack, multiple cracks, and a mixture of them. Second, the trajectory phase feature is extracted from the vectorized axis trajectories, and the frequency spectra of trajectory phase angles under different rotor faults are analyzed through Fourier transform. Finally, a parameter-optimized VMD method combined with a LightGBM model is applied to classify multiple faults of rotor systems in different noisy environments based on the extracted trajectory phase feature. The 12 rotor states can be classified into nine categories based on the harmonic information of 1X–7X components (X is the rotating frequency of a rotor system) and other components with smaller amplitudes in the frequency spectra of trajectory phase angles. The average classification accuracy of the 12 rotor states exceeds 93.0%, and the recognition rate for each kind of fault is greater than 77.5% in noisy environments. The simulated and experimental results demonstrate the effectiveness and adaptability of the proposed multi-fault classification method. This work can provide a reference for the condition monitoring and fault diagnosis of rotor systems in engineering. </jats:p