•Different types of controllable journal bearings are listed and described.•Various applications of controllable bearings are mentioned.•A comparison between passive and controllable bearings was ...made.•Advantages and disadvantages of controllable bearings are presented.•Possible directions of the future development of controllable bearings are indicated.
Controllable/active bearings are mainly associated with active magnetic bearings (AMBs), whereas active bearing control is also found in many types of bearings, e.g. fluid, gas and hybrid bearings. The article presents a review of the literature describing the structure and results of studies of active bearings. Active control brings a number of benefits resulting in the fact that their use as a support for rotors becomes increasingly common. This article introduces readers to the different methods of controlling radial bearings and provides detailed information on various technical solutions. Furthermore, the paper presents the characteristics of bearings as well as the basic advantages, disadvantages and possibilities offered by active control of various types of bearings. The influence of active control on rotor dynamics as well as on bearing friction, temperature control, permissible operating time, the environment (possibility of using safer lubricants) and operating safety is presented. The final part of the article presents possible directions of development of active bearings (ABs).
This reprint focuses on the hot issue of bearing lubrication and thermal analysis, and brings together many cutting-edge studies, such as bearing multi-body dynamics, bearing tribology, new ...lubrication and heat dissipation structures, bearing self-lubricating materials, thermal analysis of bearing assembly process, bearing service state prediction, etc. The purpose of this reprint is to explore recent developments in bearing thermal mechanisms and lubrication technology, as well as the impact of bearing operating parameters on their lubrication performance and thermal behavior.
In recent years, turbochargers have gained importance in the automotive industry, locomotive, and marine applications powered by diesel engines. Also, they are widely implemented in aerospace ...applications to enhance the engine's performance. The lightweighted turbochargers are implemented in aerospace and automotive industries having a rotational speed above 150,000 rpm; meanwhile, the turbochargers implemented in marine and locomotive applications are heavily sized, with rotational speeds around 30,000 rpm. By recovering waste energy from exhaust gases, the turbocharger provides higher inlet air pressure and mass to the engine and, in turn, boosts engine efficiency and reduces emissions. Bearings such as floating ring bearings, rolling element bearings, hydrodynamic bearings and gas foil bearings are the commonly supported bearings for turbochargers which can operate at higher speeds and are strongly nonlinear. However, while running, the rotor vibrates at sub-synchronous frequencies due to fluid instabilities. Instabilities occur in rotors mainly because of unbalanced, whirl, and whip phenomena of oil. Hence, along with the nonlinear and stability analysis, the thermo-mechanical effects must analyze thoroughly for better performance and improvement in the turbocharger's efficiency. The proposed study thoroughly reviews various analyses for a turbocharger rotor system assisted on the bearings mentioned above with different operating conditions. It explains the influence of the thrust bearing on the turbocharger dynamics. Further, the report includes additional guidelines on research topics that must explore extensively in the upcoming years.
Classical air foil bearings consist of a top foil, which is usually supported by a bump or beam foil structure. For this bearing type, the air gap is a function of the top foil deformation. Here, an ...alternative air bearing design – called air ring bearing – is investigated, which may be regarded as a straightforward and very obvious modification of the classical air bearing design. The basic idea is to insert a rigid ring between the shaft and the foil structure. The ring may therefore be considered to be elastically mounted in the housing by means of a bump or beam-type structure. Alternatively, a viscoelastic supporting structure (elastomer) may be used to connect the ring with the housing. Hence, the air film is separated by a rigid ring from the supporting structure. As a consequence, the bearing gap for the fluid film has rigid walls, which simplifies the numerical calculation significantly.
In this manuscript, a detailed numerical analysis of rotor systems supported in air ring bearings is presented. The basic nonlinear dynamical effects occurring in such rotor systems are investigated with a particular focus on the stability and bifurcation behavior. Therefore, a detailed co-simulation model of the rotor/bearing system is used. Different possible bifurcation scenarios are described and explained with the help of run-up simulations.
Rotor systems with air ring bearings exhibit a completely different vibration and stability behavior than rotors in classical air foil bearings. Diverse interesting nonlinear vibration phenomena, not known in connection with classical air foil bearings, are discussed in detail and physically explained in a clear manner.
•A nonlinear prediction model of the herringbone grooved journal gas bearing (HGJB) rotor system was built.•The proposed nonlinear theoretical model was validated by comparing it with experimental ...results.•The evolution of the self-excited motion with operating speed for the HGJB-rotor system was investigated.•The effect of static load and imbalance load on the response of HGJBs supported rotor was studied.
The nonlinear behavior of a rigid rotor supported by herringbone grooved journal gas bearings (HGJBs) was investigated in this study. The two-dimensional narrow groove theory (2D-NGT) was adopted to model the HGJBs. A set of integrated rotor-bearing state equations were built by coupling the rotor motion equations and the bearing Reynolds equation. An implicit integrator with adaptive time step method was used to solve those state equations continuously. Two low-stability HGJBs were implemented to experimentally demonstrate and analyze the appearance of self-excitation motions. The theoretical model was successfully validated by the experimental data on predicting the onset speed of the sub-synchronous vibration of the HGJB-rotor system and the whirl frequency ratio. The predicted limit cycle amplitude increases as the speed increases until the rotor contacts with the bearing surface, which leads to a bearing failure. Forward conical mode dominates the self-excited motion during the whole speed range of self-excited motion. The prediction shows that the HGJB-rotor system can still operate in a stable, even though the rotor is installed vertically, i.e., without static load on the bearings. This is a distinct advantage in comparison to plain bearings. As the static load applies on the bearings increases, the onset speed of sub-synchronous vibration increases as well. For the investigated rotor-bearing system, an increase of the onset speed of sub-synchronous vibration from 36 krpm to 75 krpm is predicted as the static load increases from 0 to 4 times of the rotor weight. This indicates an increased HGJB stability with increased static load. The rotor orbits show complex shapes when the imbalance excitation is considered in the simulation. Both synchronous frequency and whirl frequency are shown in the spectral analysis. Moreover, the speed range of self-excited motion reduces from 38,48 krpm to 40,42 krpm as the imbalance increases from 0 to 40 mgmm.
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•Introduction of the over-skidding phenomenon that occurs in angular contact ball bearings for high axial loads.•Accurate skidding and over-skidding modeling by using a ...kinematic-Hertzian-thermo-hydro-dynamic model.•Experimental validation on a large-scale test-bench in many different operating conditions.•Analysis of pure rolling condition and suitable indices for determining actual pure rolling.
From a kinematic point of view, rolling elements should continuously roll on the raceways of rolling element bearings. When the dynamic behaviour is also considered, pure rolling occurs if the bearing is properly loaded and the system is correctly lubricated. In the absence of these conditions, the rolling elements may slide, or skid, from time to time. In the literature, this behaviour is well documented and occurs generally for low-load roller bearings. During a long-lasting experimental test on a large-scale industrial angular contact ball bearing (ACBB), not only skidding behaviour but also so-called over-skidding behaviour was observed on the rolling elements of the bearing. The term over-skidding, or negative-skidding, means that the cage/rotor speed ratio exceeds the value calculated under pure rolling kinematic conditions. To the best of authors’ knowledge, this phenomenon has not been fully described or analysed before. Therefore, a comprehensive model considering the kinematics of the bearing components, the Hertzian contact between the rolling elements and raceways, the interaction between the rolling elements and cage, the hydro-dynamic lubrication, and the thermal effects is introduced in this paper to study and forecast the over-skidding and skidding mechanisms. The model acronym is KH-THD, that is the kinematic-Hertzian-thermo-hydro-dynamic model. The empirical existence of over-skidding indicates that the use of the theoretical value for the cage/rotor speed ratio is inaccurate for determining whether the bearing rolling elements are slipping or not on the raceways, especially for large-scale industrial bearings. The results of the experimental tests on such kinds of bearings obtained by varying the load and under three different operating rotational speeds and two lubricant supply conditions suggest that the KH-THD model is more accurate than existing models, which neglect the thermal effects due to friction. The analysis of the friction thermal effects due to skidding shows that a considerable temperature gradient forms in the bearing. The increase in the lubricant flow rate can somehow mitigate the increase in temperature even though it can worsen the skidding. The proposed model is useful for determining this trade-off for a given load.
•An extended and up-to-date review on bearing fault assessment (BFA) is provided.•Detailed information on signal processing and learning approaches is given.•Fault size and damage degradation ...estimation are stated as the main aims in BFA.•VIB, AE, CUR and VOLT are found as the main signals to extract useful information.•Open problems and challenges on this research topic are discussed.
Health condition monitoring of rotating machinery is a crucial task to guarantee reliability in industrial processes. In particular, bearings are mechanical components used in most rotating devices and they represent the main source of faults in such equipments; reason for which research activities on detecting and diagnosing their faults have increased. Fault detection aims at identifying whether the device is or not in a fault condition, and diagnosis is commonly oriented towards identifying the fault mode of the device, after detection. An important step after fault detection and diagnosis is the analysis of the magnitude or the degradation level of the fault, because this represents a support to the decision-making process in condition based-maintenance. However, no extensive works are devoted to analyse this problem, or some works tackle it from the fault diagnosis point of view. In a rough manner, fault severity is associated with the magnitude of the fault. In bearings, fault severity can be related to the physical size of fault or a general degradation of the component. Due to literature regarding the severity assessment of bearing damages is limited, this paper aims at discussing the recent methods and techniques used to achieve the fault severity evaluation in the main components of the rolling bearings, such as inner race, outer race, and ball. The review is mainly focused on data-driven approaches such as signal processing for extracting the proper fault signatures associated with the damage degradation, and learning approaches that are used to identify degradation patterns with regards to health conditions. Finally, new challenges are highlighted in order to develop new contributions in this field.
Grease life in hybrid bearings is longer than that in all-steel bearings. This will be shown in this article by means of grease life tests with a large number of greases for both deep groove ball ...bearings (DGBBs) and cylindrical roller bearings (CRBs). The results show that grease life for hybrid bearings is always larger than that for equivalent all-steel bearings and that this varies between a factor of 2 and 9 depending on the grease type used. For cylindrical roller bearings, grease life does not increase with decreasing speed below a minimum value. However, at these relatively low speeds, hybrid bearings give a longer grease life than all-steel bearings.
•Unknown fault feature extraction of rolling bearing is realized under variable speed conditions.•Statistical complexity measuresselects the optimalintrinsic mode function component.•Compared with ...spectral amplitude modulation have optimal performance.
As the main transmission components of rotating machinery, rolling bearings have important research significance for fault diagnosis and state detection. However, the operating environment of mechanical equipment is complex, and the fault characteristic information of rolling bearings is often unknown. Through the complex transmission path, the bearing seat vibration sensor picks up the fault vibration response is weaker, and it is often submerged by strong noise. When the speed and load of rotating mechanical equipment change, the fault characteristic of rolling bearings is more obvious under variable speed conditions. The fault diagnosis problem of rolling bearings needs to be solved urgently under strong noise background, variable speed, and unknown fault characteristics. Therefore, this paper studies an unknown fault feature extraction method of variable speed rolling bearing based on statistical complexity measures (SCM). Order analysis preprocesses the variable speed vibration signal of rolling bearings. It is convenient for subsequent fault feature extraction and analysis. The SCM selects the optimal intrinsic mode function (IMF) component corresponding to the Empirical mode decomposition (EMD) decomposition, and it is also evaluated index for the optimal response of stochastic resonance. Therefore, the adaptive frequency shift stochastic resonance effectively extracts the unknown fault features of rolling bearings under strong noise background.
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