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The low-pressure rotor system of an aircraft engine includes a fan rotor and a low-pressure turbine rotor, which are connected and fixed by a gear coupling. The existence of machining errors and assembly errors can cause rotor assembly misalignment, which is one of the important factors causing aircraft engine failures. Based on the finite element matrix set theory, this paper establishes a dynamic model of the aircraft engine rotor system, including the climbing maneuver load, nonlinear contact force of bearings, oil film force of SFDs, gravity field, additional force caused by coupling misalignment, and rotor misalignment imbalance force, considering the climbing maneuver load. Using Newmark-β algorithm to solve the misaligned rotor system model with SFDs. The influence of misalignment stiffness, clearance of the oil film, and bearing clearance on the motion state of the rotor system were analyzed in detail through bifurcation diagrams, axis trajectory diagrams, and frequency spectra. And analyze and cross compare the effects of three influencing factors on the system motion state under different maneuvering load environments. Through comparative analysis, it was found that among these three influencing factors, the misalignment stiffness of the sleeve coupling has the smallest effect on the system's motion state, but an appropriate intermediate value needs to be selected. The effect of rolling bearing clearance on the system's motion state is small and regular, while the impact of oil film clearance on the system's motion state is large and complex. The research results of this paper can provide theoretical support for parameter selection in the simulation and design of dynamic phenomena with misalignment faults in aircraft engines during maneuvering flight. [ABSTRACT FROM AUTHOR]

The performance of a rotor system is influenced by various design parameters that are neither precise nor constant. Uncertainties in rotor operation arise from factors such as assembly errors, material defects, and wear. To obtain more reliable analytical results, it is essential to consider these uncertainties when evaluating rotor performance. In this paper, the Chebyshev interval method is employed to quantify the uncertainty in the steady-state response of the rotor system. To address the challenges of high-dimensional integration, an innovative sparse-grid integration method is introduced and demonstrated using a rotor tester. The effects of support stiffness, mass imbalance, and uncertainties in the installation phase angle on the steady-state response of the rotor system are analyzed individually, along with a comprehensive assessment of their combined effects. When compared to the Monte Carlo simulation (MCS) method and the full tensor product grid (FTG) method, the proposed method requires only 68% of the computational cost associated with MCS, while maintaining calculation accuracy. Additionally, sparse-grid integration reduces the computational cost by approximately 95.87% compared to the FTG method. [ABSTRACT FROM AUTHOR]

Rotor system unbalance is one of the most important factors that affects the operating accuracy and stability in aerospace engineering. The extraction and identification of unbalanced features is the premise for the dynamic balance of rotor system. In order to accurately identify the unbalanced vibration feature, based on the fused cross‐correlation fast Fourier transform (FC‐CFFT) method, an unbalanced feature extraction method of the rotor system is proposed. The convolution window weighs the data of the vibration sequence and carries out delay processing. Through spectrum calculation, the phase information of the vibration signal is obtained. And the amplitude information of the vibration feature can be acquired through cross‐correlation calculation. The unbalanced features of the rotor system vibration signals are identified under different working conditions through simulation and experiment. The results show that this method is more accurate than FFT, the cross‐power method, and the sine‐approximation method in extracting different unbalanced vibration features of the rotor system. The extraction accuracy of unbalanced feature phase and amplitude reaches 98.61% and 97.27%, respectively. After the unbalanced feature is extracted, the dynamic balance experiment can be carried out. The unbalanced feature is used for dynamic balance compensation. In this way, the average amplitude decreased by 76.35%. The high accuracy of the FC‐CFFT method for extracting the unbalanced feature has been verified. This research provides a theoretical foundation for the vibration signal processing and dynamic balance control of the rotor system. [ABSTRACT FROM AUTHOR]

When it comes to practical engineering, there is a high likelihood of shafts developing slant cracks due to torque transmission. These cracks exhibit breathing characteristics, repeatedly opening and closing under gravity and radial forces. To diagnose rotor systems with breathing slant cracks, the nonlinear output frequency response functions (NOFRFs) method is introduced. Firstly, a dynamic model of rotor systems with breathing slant cracks is established, and the system's frequency spectra are obtained by solving the model with different crack angles, depths, and positions. Secondly, the NOFRFs values at different orders are derived based on the NOFRFs theory. The simulation results display increased nonlinear characteristics with crack angle and depth. The system's nonlinear characteristics are stronger when cracks are closer to the disk. The G 3 (j ω F) ¯ value for the first-order is sensitive to crack angles, the G 4 (j 2 ω F) ¯ value for the second-order is sensitive to crack depths, and the G 4 (j 4 ω F) ¯ value for the fourth-order is sensitive to crack positions. As a result, the NOFRFs response at different orders can detect variations in angles, depths, and positions of the breathing slant crack. Finally, experiments are conducted on a rotor system with breathing slant cracks, and the results match those of the simulation, indicating that the NOFRFs method is feasible for identifying breathing slant cracks. [ABSTRACT FROM AUTHOR]

Aiming at the difficulty of feature extraction of rotor vibration signals under strong noise, a fault diagnosis method based on mesh search variational mode decomposition (VMD) parameters combined with fine composite multiscale spread entropy (RCMDE-Relieve-F) is proposed. Based on time-domain energy entropy, kurtosis and Pearson correlation coefficient, a new index grid was formed to search VMD to decompose the optimal K of the original signal, a value was reconstructed, RCMDE in the reconstructed signal was extracted as the characteristic value, and input was filtered into the generalized regression neural network (GRNN) for training and fault pattern recognition using Relief-F dimensionality reduction. The effectiveness of VMD noise reduction parameter selection was verified by numerical simulation and comparison with other decomposition methods. Moreover, the fault simulation experiment results showed that compared with other algorithm models, the mesh search-optimized VMD combined with the RCMDE-Relief-F-GRNN method could effectively filter noise with accuracy of 96 %. [ABSTRACT FROM AUTHOR]

Impact loads affect the operational performance and safety life of rolling equipment's connecting-shaft rotor system, even causing faults and accidents. Therefore, recognizing and investigating impact loads is of great significance. Hence, a load recognition method based on motor current information is proposed in this paper to recognize impact loads on the connecting-shaft rotor system. First, the fast Fourier transform is used to obtain the frequency domain information for the motor's current response signal from the rotor system load recognition test. Consequently, the required load response information can be presented more clearly using the singular value decomposition method to remove the power frequency components in the current signal. Then, wavelet packet decomposition is performed on the signal to generate energy analysis feature vectors. A qualitative recognition of the impact load on the system is achieved by learning vector quantization neural networks; the resulting load recognition results are good. These findings indicate that using the motor current as the analysis signal can solve the problem of the difficult layout for traditional vibration sensors in rolling sites. The preprocessing and recognition method of the current response signal can recognize the impact load, confirming the applicability and feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

Various processes take place in rotor systems with tilting pad bearings. It is important not only to control but also to manage these processes. Due to the instability of the oil film layer in a bearing with inclined pads, oil whirl/whip can occur. Such whirl/whip destabilize the operation of the rotor system. Additional elastic elements between the tilt pads suppress oil whirl/whip and thus reduce rotor vibration excitation. By identifying the working zones of such bearings where oil whirl and whip occur, the problems of rotor rotation instability can be solved. In order to determine the effectiveness of the elastic elements between the tilting pads, research was conducted. A special stand with diagnostic equipment was used for the tests. The clearance between the rotor and the bearing was 50 μm. During the research, the rotor rotation speed was varied from 0 to 5000 rpm. After conducting the research, stable and unstable rotor working zones were determined (Zone I: 0 to 1938 rpm; Zone II: 1938–3923 rpm; Zone III: 3923–5000 rpm). Based on the obtained research results, it is possible to control the working process of the rotor system. [ABSTRACT FROM AUTHOR]

Sealing aerodynamic characteristics are affected by the seal structure, and thus the stability of the rotor system is affected too. A 1.5-stage, three-dimensional, full-cycle model of the high-pressure cylinder of a 1000 MW steam turbine was established. The high eccentricity whirl of the rotor was realized using mesh deformation technology and the multi-frequency whirl model. The nonlinear steam-flow-exciting force of different sealing structures was obtained using CFD/FLUENT, and the motion equations with a nonlinear steam-exciting force were solved using the Runge–Kutta method. The motion characteristics and stability of the rotor system with different sealing structures were obtained. The results show that there are "inverted bifurcation" and "double bifurcation" phenomena in the bifurcation diagrams of different tooth numbers, boss numbers, and tooth lengths, and a 1/2 power frequency of different sealing structures goes through the process of weakening, disappearing, reproducing, and evolving into a 1/3 power frequency and a 2/3 power frequency. With the increasing load, the steam-flow-exciting force becomes stronger, and the multi-frequency vibration and dense frequency phenomena are significant. Under some load conditions, the change curves of three kinds of teeth in 1/3 and 2/3 power frequency vibrations are highly similar, and the tooth number has little influence on the system stability. Under the high load condition, with the boss number increasing, the chaos phenomenon is weakened. Increasing the tooth length is beneficial to the stability of the rotor. [ABSTRACT FROM AUTHOR]

[Objective] To improve the design efficiency of the mechanical structure of the rotor system of a rubber roller husker. [Methods] An auxiliary calculation system for the rotor system design parameters of a rubber roller husker （RRHRSPD） that can be independently installed and operated under the Windows system was developed using VB and Matlab platforms. Based on the equivalent design method and the traditional mechanical design method, the coupling relationships among the technological parameters, dynamic parameters and structural parameters of the husker were established, and the calculation principle of the structural parameters of the rotor system was also explored. VB was used to develop the software operation interface and to quickly call the Matlab dynamic link library, which formed the core computing mechanism of the system, and the system was packaged and released. [Results] A set of auxiliary calculation system for structural parameters of the rotor system of rubber roller husker was developed. [Conclusion] The calculation results of the system are accurate and reliable, which can be used not only for the design and calculation of the rotor system structure of the rubber roller husker, but also for the virtual test platform for the performance analysis of the rubber roller husker.

The operational state of a rotor system directly affects its working efficiency, and the axis trajectory can accurately characterize this state. Therefore, a method for extracting axis motion trajectory characteristics based on distance sequence representation is established. First, the axis trajectory sample signal is constructed from the original vibration displacement signal. Singular value decomposition (SVD) is performed on the sample signal to obtain effective components, resulting in a purified and denoised axis motion trajectory signal. Next, the axis motion trajectory signal is centralized and normalized. Feature extraction is then performed on the axis motion trajectory signal. Based on the different curvatures of various regions in the axis motion trajectory graph, data points are adaptively selected. The distances between the selected data points and a unique fixed point are calculated in the two-dimensional plane, resulting in a feature signal that characterizes the axis motion trajectory graph. This completes the extraction of the axis motion trajectory characteristics. Different rotational speeds, additional weights, and changes in rotor arrangement types are applied to a multi-disk rotor test rig to obtain measured data for various unbalanced states, validating this method. The results show that this method effectively characterizes the axis motion trajectory with strong generality. [ABSTRACT FROM AUTHOR]

The blade fracture of horizontal centrifugal pump will not only affect the hydraulic performance of the pump, but also affect the safety and stability of the whole unit. In this paper, for horizontal centrifugal pumps, five single-blade fracture schemes are designed and numerical simulations are carried out under different operating conditions. The results show that with the increase of fracture size, the influence on the hydraulic characteristics of the pump shows a decreasing trend, and it will also affect the turbulent kinetic energy distribution near the impeller inlet, so that the internal flow becomes complex and the flow loss increases. The radial force on the impeller changes periodically, and its magnitude shows a nonlinear decreasing change with the increase of the fracture size. The pressure pulsation analysis of several monitoring points in the worm shell shows that as the fracture size increases, the amplitude of the lobe frequency slowly rises, and the shaft frequency, which is second only to the lobe frequency, becomes higher and higher and begins to dominate. A study of the rotor system shows that the maximum deformation of the impeller occurs at the edge of the impeller cover and the maximum equivalent stress occurs at the blade exit; blade fracture causes a significant reduction in the latter third-order intrinsic frequency. [ABSTRACT FROM AUTHOR]

The nonlinear stiffness of a structure results in complex nonlinear dynamic behaviors and bifurcations of rotor systems. However, there still lacks of comprehensive studies on the bifurcation-induced motion to chaos of the nonlinear system. This study investigated the energy transfer during the motion evolution to chaos around bifurcations. In this paper, a flexible rotor system with nonlinear stiffness is established and the nonlinear responses under different parameter excitations are studied. We construct the energy trajectory in energy space and propose a bifurcation detection method based on generalized energy transfer for studying the evolution of motion cascades to chaos. The induction of period-doubling and period-halving bifurcation is revealed through the energy trajectory. The stability domains of the rotor system in different parameter planes are determined based on the Lyapunov stability criterion. A nonlinear rotor test platform is built and speed-up experiments are carried out to verify the proposed bifurcation detection method based on generalized energy transfer. These results indicate that the energy transfer is consistent with the switching of bifurcations. The sudden shift and fluctuation in the generalized energy amplitude correspond to period-doubling bifurcation and chaos, respectively. The generalized energy curves reveal the period-halving bifurcation, which cannot be observed in the speed-up test. This research and proposed method have potential for application in condition monitoring and bifurcation recognition during the operation of rotating machinery. [ABSTRACT FROM AUTHOR]

In order to solve the problem of imbalance of internal forces in the system caused by the gravity force of the eccentric wheel and the orbiting scroll close to the drive bearing and the rotational inertia force during the operation of the electric scroll compressor, a dynamic model of the rotor system of the scroll compressor that takes into account the effect of the gas force was established using the multibody dynamics software ADAMS/View 2020. Dynamic simulation analysis of the rotor system is carried out, focusing on the force of the drive bearing; a parametric optimization method is adopted to optimize the position of the center-of-mass coordinates of the eccentric wheel of the relevant components, and the relevant parameters are derived after optimization. The results show that by adjusting the center-of-mass position of the eccentric wheel it is possible to optimize the unbalance force and unbalance moment of the main shaft drive system; compared with the pre-optimization, the force fluctuation ranges of the drive bearing in the horizontal and vertical directions are reduced, the peak value is reduced by 18%, and the impact force of the drive bearing during the initial period of compressor operation is effectively relieved. Through optimization calculation, the vibration and noise of the system are reduced, the operating stability of the scroll compressor is improved, and analytical methods and theoretical guidance are provided for the design and prediction of the dynamic behavior of the scroll compressors. [ABSTRACT FROM AUTHOR]

Along with the rotating machinery advances toward high speeds, the significance of the excitation force of the seal fluid in the rotor system is growing, which can cause serious accidents. Most of the previous research on rotors in rotating machinery has predominantly focused on the effects of misalignment in couplings. In this article, a novel model is proposed, introducing an analytical approach that combines both internal friction in couplings and loosening support faults. Additionally, an analysis and discussion of the vibration characteristics of the rotating system under the influence of internal friction are presented. This method allows for a more comprehensive assessment of the performance of rotors in engineering applications. Assuming that the left support of the rotor is loose, this model focused on how various factors such as rotor speeds, eccentricity, seal disc mass, and left-end support mass affect the labyrinth seal rotor system's dynamic characteristics. Based on the findings, The emergence of internal friction forces advances the chaos of the rotor. It seems that as the rotating speed increases, there will be a small frequency range, resulting in fluid oscillation, and the system stability will be reduced at this time. The improvement in the seal disc's quality has minimal impact on the stability of the left journal, but it will reduce the stability of the seal disc. The increase in the mass of the left end support will increase the stability of the movement at the left journal and reduce the stability of the movement at the seal disc. [ABSTRACT FROM AUTHOR]

This paper proposes a novel cylindrical conformal contact model for the large-diameter bearing with small clearance to its housing in aero-engines. Since the clearance between them is usually below one-thousandth of the bearing nominal diameter, Hertz's law is not feasible in this case. The proposed contact model accounts for the surface contact condition and more geometric parameters of the bearing-housing component to obtain more accurate prediction results, which are validated by the finite element method (FEM) results. Based on this novel contact model, the vibration response of a single-disk rotor introduced by Ishida et al. is investigated. Numerical results are in good agreement with experimental results by Ishida et al. Influences of several critical parameters on the vibration responses are also studied. Furthermore, a complex dual-rotor system whose front bearing has a clearance stop between the outer ring and housing is analyzed with the proposed model. Good agreement is shown in the comparison between numerical and experimental results, which shows the feasibility of the proposed model in the contact simulation of large-diameter bearings with a small clearance. The results show that periodic collision between the bearing and housing could lead to self-excited vibrations. A natural frequency component in frequency-domain responses is an important indicator for the occurrence of self-excited vibration. This work provides a reference for the fault diagnosis of practical rotor-bearing systems with bearing clearance. [ABSTRACT FROM AUTHOR]

The twin rotor aerodynamic system (TRAS) reflects the dynamics of vertical take-off rotor systems. TRAS considers the coupling effect and gyroscopic disturbance torque as unwanted signals. For safe and reliable TRAS operation, proper control input is vital, along with fast fault indication. This paper addresses the output sensor fault detection problem in the linear model of TRAS subjected to l2-norm bounded disturbance. A robust design of an observer is formulated as H-/H∞ optimization problem to maximize the sensitivity/robustness criterion. The approach minimizes the disturbance effect on the residual signal, which leads to successful fault detection. Furthermore, a linear quadratic regulator-based state feedback controller is proposed to meet the system's desired transient response requirement. The incorporation of an observer-based residual generator for fault detection along with the state-feedback controller differs the current work from the existing work. Successful fault detection in the output sensor of TRAS depicts the good performance of the proposed observer.

The performance of a rotor system is influenced by various design parameters that are neither precise nor constant. Uncertainties in rotor operation arise from factors such as assembly errors, material defects, and wear. To obtain more reliable analytical results, it is essential to consider these uncertainties when evaluating rotor performance. In this paper, the Chebyshev interval method is employed to quantify the uncertainty in the steady-state response of the rotor system. To address the challenges of high-dimensional integration, an innovative sparse-grid integration method is introduced and demonstrated using a rotor tester. The effects of support stiffness, mass imbalance, and uncertainties in the installation phase angle on the steady-state response of the rotor system are analyzed individually, along with a comprehensive assessment of their combined effects. When compared to the Monte Carlo simulation (MCS) method and the full tensor product grid (FTG) method, the proposed method requires only 68% of the computational cost associated with MCS, while maintaining calculation accuracy. Additionally, sparse-grid integration reduces the computational cost by approximately 95.87% compared to the FTG method.

Sealing aerodynamic characteristics are affected by the seal structure, and thus the stability of the rotor system is affected too. A 1.5-stage, three-dimensional, full-cycle model of the high-pressure cylinder of a 1000 MW steam turbine was established. The high eccentricity whirl of the rotor was realized using mesh deformation technology and the multi-frequency whirl model. The nonlinear steam-flow-exciting force of different sealing structures was obtained using CFD/FLUENT, and the motion equations with a nonlinear steam-exciting force were solved using the Runge–Kutta method. The motion characteristics and stability of the rotor system with different sealing structures were obtained. The results show that there are “inverted bifurcation” and “double bifurcation” phenomena in the bifurcation diagrams of different tooth numbers, boss numbers, and tooth lengths, and a 1/2 power frequency of different sealing structures goes through the process of weakening, disappearing, reproducing, and evolving into a 1/3 power frequency and a 2/3 power frequency. With the increasing load, the steam-flow-exciting force becomes stronger, and the multi-frequency vibration and dense frequency phenomena are significant. Under some load conditions, the change curves of three kinds of teeth in 1/3 and 2/3 power frequency vibrations are highly similar, and the tooth number has little influence on the system stability. Under the high load condition, with the boss number increasing, the chaos phenomenon is weakened. Increasing the tooth length is beneficial to the stability of the rotor.

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Severe looseness and unbalance of a twin-spool rotor system aggravate the vibration of the entire system, which may induce secondary faults such as intershaft rubbing. To address this issue, the dynamic responses of a twin-spool rotor–casing system with looseness and intershaft rubbing coupling faults are analyzed. First, considering nonlinear factors, such as looseness and intershaft rubbing force, the governing equations of the twin-spool rotor–casing system are derived based on the finite element discretization method. To deal with second-order nonlinear differential equation, a modified Newmark-β method based on Gaussian elimination is proposed. On this basis, the effects of looseness and intershaft rubbing fault on the dynamic responses of the rotor system are discussed through numerical simulations. Results indicate looseness fault increases the vibration of the rotor system. As the support stiffness decreases, the rotational orbit becomes irregular and complex, and the displacement in the vertical direction varies remarkably. Moreover, looseness can cause the rotor system to induce the secondary intershaft rubbing fault. Compared with the rotor system without looseness, the rotational speed corresponding to the first intershaft rubbing drops due to the effect of looseness. As the initial intershaft clearance grows, most of partial rubbing states evolve into no rubbing, and the possibility of intershaft rubbing decreases. [ABSTRACT FROM AUTHOR]

For the squirrel cage in aero-engine, a metamaterial attenuation structure is presented to control its vibration. Considering the characteristic rotating speeds of rotor system, several types of metamaterial cells are designed. According to the shape of squirrel cage, a structure composed of the metamaterial belts is designed to realize vibration attenuation. For each cell, the dispersion analysis is carried out. The results prove that the bandgap could cover the characteristic frequency of the rotor system. For the squirrel cage equipped with the metamaterial belts, corresponding Finite Element Method (FEM) model is established and simulations are carried out. The results prove that the metamaterial belts could attenuate the cage's vibration effectively. The validation experiments were carried out. The results of sweeping frequency prove that the metamaterial structure could attenuate the vibration amplitude significantly. Especially, at the resonance frequency, the squirrel cage with metamaterial belts could reach a 96% reduction in amplitude compared to the squirrel cage without it. The responses for harmonic excitations prove that at the characteristic rotating speed the vibration amplitude of squirrel cage can be reduced greatly. The results may provide a guidance for the design of vibration attenuation of squirrel cage. [ABSTRACT FROM AUTHOR]

In order to improve the vibration performance of the oil-lubricated tilting pad bearing system, an experimental approach using a piezoelectric actuator to control two new flexible tilting pads is proposed. The performance test bench of the bearing–rotor system based on a tilting pad bearing with a flexible support is established. The different circumferential angles of the angle bearing tilting pad and the radial displacement of the displacement bearing are tested by a piezoelectric actuator. At the same time, the trajectory of the rotor center under actual operating conditions is analyzed. The experimental results show that the amplitude of the rotor journal can be significantly reduced by controlling the control variables related to the circumferential angle and radial displacement of the bearing bush. Therefore, this control improvement can improve the vibration performance of two new flexible tilting pad bearing–rotor systems. The technical means are provided for the active control of an oil-lubricated tilting pad bearing. [ABSTRACT FROM AUTHOR]

To solve the problems of the nonlinear damping force in the traditional squeeze film damper (SFD), a novel structure of G-type integral squeeze film damper (GISFD) based on ISFD is proposed for the first time. The finite element model and test rig of the ball bearing-rotor system are established to explore the influence of GISFD and ISFD on the dynamic characteristics of the unbalanced rotor system. The results show that both GISFD and ISFD can change the critical speed of the rotor system, reduce the bending strain energy of the shaft, and reduce the bearing dynamic load of the rotor system. Through comparison, it is found that the effect of GISFD is more obvious. The experimental results show that, compared with the unbalanced rotor system without damper, the peak-peak value of amplitude in the rotor system with GISFD and ISFD at 3000 rpm is reduced by 25.53 and 15.81%. The amplitude in the disk at the first-order critical speed is effectively reduced, and the reduction range reach 52.01 and 35.44%, respectively. GISFD has a more significant effect of suppressing unbalanced vibration, and has superior vibration damping performance when compared with ISFD. [ABSTRACT FROM AUTHOR]

The operational state of a rotor system directly affects its working efficiency, and the axis trajectory can accurately characterize this state. Therefore, a method for extracting axis motion trajectory characteristics based on distance sequence representation is established. First, the axis trajectory sample signal is constructed from the original vibration displacement signal. Singular value decomposition (SVD) is performed on the sample signal to obtain effective components, resulting in a purified and denoised axis motion trajectory signal. Next, the axis motion trajectory signal is centralized and normalized. Feature extraction is then performed on the axis motion trajectory signal. Based on the different curvatures of various regions in the axis motion trajectory graph, data points are adaptively selected. The distances between the selected data points and a unique fixed point are calculated in the two-dimensional plane, resulting in a feature signal that characterizes the axis motion trajectory graph. This completes the extraction of the axis motion trajectory characteristics. Different rotational speeds, additional weights, and changes in rotor arrangement types are applied to a multi-disk rotor test rig to obtain measured data for various unbalanced states, validating this method. The results show that this method effectively characterizes the axis motion trajectory with strong generality.

In order to solve the problem of imbalance of internal forces in the system caused by the gravity force of the eccentric wheel and the orbiting scroll close to the drive bearing and the rotational inertia force during the operation of the electric scroll compressor, a dynamic model of the rotor system of the scroll compressor that takes into account the effect of the gas force was established using the multibody dynamics software ADAMS/View 2020. Dynamic simulation analysis of the rotor system is carried out, focusing on the force of the drive bearing; a parametric optimization method is adopted to optimize the position of the center-of-mass coordinates of the eccentric wheel of the relevant components, and the relevant parameters are derived after optimization. The results show that by adjusting the center-of-mass position of the eccentric wheel it is possible to optimize the unbalance force and unbalance moment of the main shaft drive system; compared with the pre-optimization, the force fluctuation ranges of the drive bearing in the horizontal and vertical directions are reduced, the peak value is reduced by 18%, and the impact force of the drive bearing during the initial period of compressor operation is effectively relieved. Through optimization calculation, the vibration and noise of the system are reduced, the operating stability of the scroll compressor is improved, and analytical methods and theoretical guidance are provided for the design and prediction of the dynamic behavior of the scroll compressors.

For the aero-engine rotor system with complex vibration responses, a simplified model based dynamic similarity is proposed to study the vibration characteristics of that. On the basis of the principle of dynamic similarity, a simplified model of the combustion-driven rotor is obtained, with the criteria of the same critical speed of each order and similar vibration modes, while keeping the layout of the structure unchanged. By comparing the vibration characteristics of the actual rotor with those of the simplified model through theoretical analysis, there is less than 2.59 % error between the simplified model and the actual rotor. The rationality of the research method, which is developing the simplified model based on dynamic similarity to study the vibration response law of the original rotor, is demonstrated. Then, the unbalance response law of the rotor with a squeeze film damper is explored expanding on the produced model, and the study shows that the unbalanced excitation can significantly reduce the response. Finally, the influence law of the phase of unbalance excitation is experimentally verified on the test rotor. The results show that the simplified model of the actual rotor based on dynamic similarity can well reflect the vibration characteristics of the original rotor, and the proposed analysis method has an important reference role in studying the vibration mechanism of the aero-engine rotor system.

The rotor systems are the critical components of many rotational machines. The dynamic stiffness of the supporting structure affects the dynamic characteristics of the rotor system significantly. The effect can't be overlooked for obtaining accurate dynamic characteristics. The judgment index of dynamic stiffness influence (DSI) is proposed in this paper to evaluate the degree of dynamic stiffness influence on the dynamic characteristics. The dynamic model of the rotor system considering the dynamic stiffness of supports is established, and the expression of DSI is given. Then the Campbell diagrams and corresponding DSI values for different system parameters under the influence of dynamic stiffness are discussed and analyzed. The effectiveness of DSI is verified by the literature. Besides, an experiment is carried out to verify the effectiveness of the DSI. The results indicate that the effectiveness of DSI can be confirmed by both numerical and experimental cases, and that the DSI can evaluate the degree of dynamic stiffness influence well. [ABSTRACT FROM AUTHOR]

The research on fault diagnosis methods based on generative adversarial networks has achieved fruitful results, but most of the research objects are rolling bearings or gears, and the model test data are almost all derived from laboratory bench test data. In the industrial Internet environment, equipment-fault diagnosis is faced with the characteristics of large amounts of data, unbalanced data samples, and inconsistent data file lengths. Moreover, there are few research results on the fault diagnosis of rotor systems composed of shafts, impellers or blades, couplings, and tilting pad bearings. There are still shortcomings in the operational risk evaluation of rotor systems. In order to ensure the reliability and safety of rotor systems, an Improved Auxiliary Classifier Wasserstein Generative Adversarial Network with Gradient Penalty (IACWGAN-GP) model is constructed, a fault diagnosis method based on IACWGAN-GP for tilting pad bearings is proposed, and an intelligent fault diagnosis system platform for equipment in an industrial Internet environment is built. The verification results of engineering case data show that the fault diagnosis model based on IACWGAN-GP can adapt to any length of sequential data files, and the automatic identification accuracy of early faults in tilting pad bearings reaches 98.7%. [ABSTRACT FROM AUTHOR]

Introduction: When the micro gas turbine surpass the first order critical, the synchronous vibration of the compressor end often exceeds the allowable value. To address this problem, a novel squeeze film damper (NISFD), containing three pairs of elastomer characteristics is designed. Compared with the conventional integral squeeze film damper, the NISFD ensures the uniform distribution of stiffness and damping, and the structure is more simpler and easier to machine. Methods: The specific implementation process is as follows: the compressor is equivalent to the rotor system and modelled. Based on the finite element method, the synchronous vibration response analysis is carried out to determine the optimal stiffness value of the damper. The stiffness of the NISFD are tuned by modifying the structural parameters. Then, based on the high precision computational fluid dynamics (CFD) method verified by experiments, the equivalent damping coefficient of the NISFD is solved and applied to the rotor system for synchronous vibration response analysis. To further verify the damping performance of the NISFD, an equivalent rotor test rig was built based on the dynamic characteristics of the compressor. Results: By comparing vibration values in the two directions of the disc end with and without the NISFD, excellent vibratio control effects are achieved under the critical speed operation conditions of the rotor system. The maximum reduction in the vibration displacement amplitude in the x direction is 74.07%, and that in the y direction is 54.69%. At the same time, the damping force provided by the damper increases with the increasing of the rotor whirl amplitude within a certain range. Conclusion: From the research work, it is found that the NISFD designed based on the optimal stiffness method can effectively suppress the whirl amplitude of the rotor and significantly improve the stability of the rotor system. [ABSTRACT FROM AUTHOR]

• A skewed distribution is introduced to build contact mechanics model more accurately. • Nonlinear vibration and bifurcations are investigated of rotor system in different preloads. • A higher preload is conducive to maintaining stable period-1 motion state at high speed. • Speed range with obvious periodic-doubling frequency increases with the increase of preload according to test results. • Such results can be applied to preload adjustment and health monitoring of gas turbine rotor systems. Contact effects are one of the primary nonlinear sources of vibrations in the gas turbine rotor systems. Specifically, the nonlinear stiffness between the disk interface from the contact effects has an important influence on the vibration characteristics. In this study, a contact model that accounts for the elastoplastic deformation of asperity is established based on the contact theory. To improve the macroscopic contact model of the bolted structure, we integrate the tested morphology results and modified the skewed distribution function. Subsequently, a dynamic model of the rod fastened rotor-bearing system that incorporates the nonlinear oil film force is established. The influence of the preload on the vibration characteristics of the rotor bearing system is analyzed. The results demonstrate that the improved contact model accurately describes the distribution of asperities on rough surface. The contact effects weaken the rotor lateral stiffness to a certain extent. According to the numerical results and experimental results, it can be found that changes in preload significantly affects the occurrence conditions from periodic vibration to chaotic vibration, a higher preload is conducive to maintaining the stable period-1 motion state at high speed. Additionally, as the preload is decreased, the speed range with obvious periodic-doubling frequencies gradually increases and the amplitude of vibration response decreases. This work provides a practical guidance for the dynamic design and preload adjustment of gas turbine rod-fastened rotor considering contact effects. [ABSTRACT FROM AUTHOR]

Axial-flow pumps consider both the conventional pump mode and the pump as turbine (PAT) mode operation and put forward higher requirements for long-term operation stability and structural strength; therefore, it is of great engineering significance to evaluate the structural strength and fatigue life of the rotor under full operating conditions. In this study, based on computational fluid dynamics and the one-way fluid-structure interaction algorithm, the structural strength and fatigue life of the rotor system of a large vertical axial-flow pump under full operating conditions were evaluated and studied. The results show that blade deformation and equivalent stress are generally higher in the PAT mode than in the pump mode. The maximum deformation in both modes occurs at the tip of the blade, while the area of stress concentration is at the root of the blade. Both the deformation and the equivalent stress increase with increasing flow rate. The minimum safety factor occurs at the blade root in both modes, and the safety factor in the PAT mode is relatively smaller than that in pump mode. Therefore, when designing and manufacturing axial flow pumps for turbine duties, priority should be given to material strength at the blade root during PAT mode operation to ensure safe and stable operation. The aim of this study is to provide technical references and theoretical foundations for evaluating the service cycle of axial-flow pumps and the influence on pump life under different operation modes. [ABSTRACT FROM AUTHOR]

The rotor of the magnetic suspension turbomachinery is supported by the magnetic suspension bearing without contact and mechanical friction, which directly drives the high-efficiency fluid impeller. It has the advantages of high efficiency, low noise, less fault and no lubrication. However, the system often has some unknown mutation, time variation, load perturbation and other un-certainties when working, and the traditional Proportion Integration Differentiation (PID) control strategy has great limitations to overcome the above disturbances. Therefore, this paper firstly establishes a mathematical model of the rotor of magnetic levitation turbomachinery. Then, a linear active disturbance rejection controller (LADRC) is presented, which can not only improve the above problems of PID control, but also avoid the complex parameter tuning process of traditional nonlinear active disturbance rejection control (ADRC). However, LADRC is easy to induce the overshoot of the system and cannot filter the given signal. On this basis, an improved LADRC with a fast-tracking differentiator (FTD) is proposed to arrange the transition process of input signals. The simulation results show that compared with the traditional PID controller and single LADRC, the improved linear active disturbance rejection control method with fast tracking differentiator (FTD-LADRC) can better suppress some unknown abrupt changes, time variation and other uncertainties of the electromagnetic bearing-rotor system. At the same time, the overshoot of the system is smaller, and the parameters are easy to be set, which is convenient for engineering application.

In this study, we developed a data-driven frequency domain analysis method for rotor systems using the NARX (Nonlinear Auto-Regressive with eXternal input) model established by system vibration signals. We propose a model-based index of fault features calculated in a multi-frequency range to facilitate condition monitoring of rotor systems. Four steps are included in the proposed method. Firstly, displacement vibration signals are collected at multiple monitored rotating speeds. Secondly, the collected signals are processed as output data and the corresponding input data is generated. Then, NARX models are developed with input and output data to characterize the rotor system. Finally, the NRSF (Nonlinear Response Spectrum Function)-based nonlinear fault index is calculated and compared to the healthy condition. An experimental application to the misaligned rotor system is also demonstrated to verify its effectiveness. Our results indicate that the value of the index directly reflects the severity of the misaligned fault. [ABSTRACT FROM AUTHOR]

In practical engineering applications, the working load of the rotor system is changing constantly, and the noise pollution of its working environment is serious, which leads to the performance degradation of traditional fault diagnosis methods. To solve the above problems, we present a novel rotor system fault diagnosis model based on parallel convolutional neural network architecture with attention mechanism (AMPCNN). The model uses convolution kernels of different sizes in parallel channels to process raw data, and based on late feature fusion, a more comprehensive feature map is obtained. Furthermore, the information sharing between the two channels is realized through the attention mechanism so that the effective features of one channel can be reflected in another channel. The performance of the model under variable working conditions is verified by the Machinery Fault Database (MAFAULDA), and the average accuracy is 99.58%. By dividing Gaussian white noise from -9 dB to 2 dB into 11 intervals and adding it to the public data of Wuhan University, the noise resistance performance is verified, and the proposed method can obtain 100% diagnosis accuracy even in the high noise condition. The above experiments show that in terms of load adaptability and noise immunity, the method has higher accuracy than traditional deep learning classification methods. [ABSTRACT FROM AUTHOR]

The digital twin (DT) includes real-time data analytics based on the actual product ormanufacturing processing parameters. Data fromdigital twins can predict asset maintenance requirements ahead of time. This saves money by decreasing operating expenses and asset downtime, which improves company efficiency. In this paper, a digital twin in braiding machinery based on IoT (DTBM-IoT) used to diagnose faults. When an imbalance fault occurs, the system gathers experimental data. After that, the information is sent into a digital win model of the rotor system to see whether it can quantify and locate imbalance for defect detection. It is possible to anticipate asset maintenance requirements withDT technology by IoT (Internet of Things) sensors, XR(XRay) capabilities, and AI-powered analytics.A DT model's appropriate design and flexibility remain difficult because of the nonlinear dynamics and unpredictability inherent in the degrading process of equipment. The results indicate that theDT in braidingmachinery developed allows for precise diagnostic and dynamic deterioration analysis. At least there is 37% growth in efficiency over conventional approaches. [ABSTRACT FROM AUTHOR]