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The vibration control of a flexible rotor by means of a squeeze-film damper
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Efficient computation on nonlinear responses of a rotating assembly incorporating the squeeze-film damper
No full textOil film forces of the squeeze-film damper are highly nonlinear functions of the displacement and velocity of the shaft. Three numerical methods are introduced to predict the dynamic characteristics of this nonlinear system. The fast integration method is very efficient in calculating the transient and steady state responses. The harmonic balance method can be used to predict steady state responses of both synchronous and nonsynchronous (subharmonic and superharmonic) components. The simple iteration method is suitable to calculate the circular concentric orbits. The method can be chosen according to the practical need
Skidding and cage whirling of angular contact ball bearings: Kinematic-hertzian contact-thermal-elasto-hydrodynamic model with thermal expansion and experimental validation
Get PDFThe occurrence of skidding and overskidding behaviour is likely to scratch rolling element raceways and lead to a significant temperature rise and thermal deformation. The ball-cage interaction and cage whirling motion are likely to oscillate as this skidding is aggravated. To address the damage problems introduced by skidding behaviour, a kinematic-Hertzian contact thermal-elasto-hydrodynamic (KH-TEHD) model with a 5-layer loop structure is proposed. Various factors are considered in the model, including the dynamic beahviour of bearing components, quasi-static analysis on bearing load distribution and deformation of bearing components, and the miscellaneous forces (unbalanced force, collision tangential friction, drag force) acting on the ball and cage. Ball-raceway lubrication, lubricant temperature rise, thermal expansion of shaft and bearing housings, and hydrodynamic pressure acting between the cage surface and guide-ring surface are established in this paper. A 7307AC bearing experimental study under varying operating speeds, axial loads and two lubricating conditions is conducted to validate the accuracy and effectiveness of the KH-TEHD model. The superiority of the developed model is illustrated by comparison with previous models, and the results suggest that the thermal expansion and cage-guide ring hydrodynamic pressure cannot be ignored. After comparisons with literature results, it is found that the overskidding degree is approximately proportional to the square of the bearing size under the same level of operating speed. The maximum thermal deformation at the bearing raceway under starvation lubrication reaches 4 times the ball-raceway clearance. The cage simulation results indicate that the cage whirling oscillation amplitude increases with increasing operating speed and unbalanced mass and generally decreases with increasing axial load. The proposed model and discussion of the results are useful for mitigating the skidding degree under certain conditions and avoiding cage instability and wear
Behaviour of an angular contact ball bearing with three-dimensional cubic-like defect: A comprehensive non-linear dynamic model for predicting vibration response
No full textThe dynamic model of an asymmetric defects on an angular contact ball bearing raceway has not been fully described before. An advanced 10-degree-of-freedom dynamic model that includes detailed contact forms between a three-dimensional cubic-like defect and balls is proposed in this article. Examples are load distributions, ball passing defect profiles, varying effective stiffness between balls and raceways, and the impulse response caused by the collision of balls and defect edges. The results suggest that the circumferential size of the 3-D defect has a significant effect on the contact force distribution, which consequently generates impulse vibration in the bearing system. The analysis on the axial and circumferential sizes of defect show that the extension of the defect in the circumferential direction should be avoided. Additionally, the reduction of the radial-axial load ratio could mitigate the vibration impulses
Deep spiking transfer learning for rotating machinery fault diagnosis
No full textTransfer learning is commonly used to find domain-invariant features between different domains. However, existing models may extract redundant and distorted features, which show poor interpretability and lead to poor performance in the target domain. To address this issue, a novel model named Multi-order Statistics Matching Gated Spiking Neural Network (MSM-HGSNN) is proposed for rotating machinery fault diagnosis. To better extract features and reduce noise in signals, an interpretable feature extraction module composed of sparse wavelet convolution and gated leaky integrate-and-fire module is proposed. Furthermore, to ensure better performance in the target domain, the multi-order statistical matching measure is proposed to align features from the source domain and target domain. Compared with traditional transfer learning methods, the proposed method demonstrates better diagnostic performance on bearing and gear datasets
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Ultra-compact triboelectric bearing based on a ribbon cage with applications for fault diagnosis of rotating machinery
No full textA ribbon-cage-based triboelectric bearing (RTB) is proposed and applied to the fault diagnosis of rotating machinery. Teflon insulating coatings are sprayed on the surface of the ribbon cage, and interdigital electrodes are pasted on the inner side of the dust cover to form a triboelectric nanogenerator with a free-standing mode. Owing to the direct use of the existing structure of rolling bearings (the ribbon cage and dust cover), only an insulating film and electrodes are added, and the designed RTB has an ultra-compact structure. Based on the fabricated RTB prototype, the variations in output voltage and current with load resistance are tested, and the effects of design parameters (including dielectric layer material and thickness, number of electrode section pairs, and spraying of Teflon coatings) on output characteristics are discussed. Through varying-speed tests, charging of load capacitors, and effective driving of micro-powered electronic devices, the
self-sensing and self-powering capabilities of the proposed RTB are confirmed. A gear transmission test bench is constructed to perform fault diagnosis of rotating machinery based on the RTB output current. Combined with the time–frequency transformation and a deep learning algorithm, typical faults of rotating machinery (including localized faults in gears and bearings) are classified and recognized. The results show that the RTB
output current can be used to diagnose faults in rotating machinery, and the classification accuracy can exceed 90%, which is only slightly lower than that obtained from the analysis using vibration signals. The proposed RTB has good application prospects for the fault diagnosis of rotating machinery
Extremely compact and lightweight triboelectric nanogenerator for spacecraft flywheel system health monitoring
No full textThe abnormal state of supporting bearings significantly affects the directional accuracy of spacecraft flywheel systems. A self-sensing triboelectric nanogenerator (TENG) offers a desirable route for on-orbit health monitoring and can potentially improve the intelligence level of spacecraft. Here, an extremely compact and lightweight TENG (CL-TENG) for the nonguided clearance of bearings is proposed and fabricated for the condition monitoring of a flywheel assembly. Using the bearing radial space allows the CL-TENG to perceive the revolution and whirling behavior of the cage; therefore, the output of the CL-TENG is simultaneously affected by the bearing speed and load. A test platform for capturing the kinematic of the cage is established to validate the effectiveness of the CL-TENG based on bearing skidding, cage rotation, and whirling instability. A negative exponential correlation between the output voltage and dynamic whirling clearance index is shown to be the basis of cage whirling sensing. The internal clearance and materials of the CL-TENG are optimized to enhance the output performance while preventing wear on the flexible electrodes. The application of the CL-TENG to an actual flywheel system in a simulated space environment and nonstationary operating conditions demonstrate its advantages in detecting the abnormal operating state of the cage
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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