Littérature scientifique sur le sujet « Bearing flexibility »
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Articles de revues sur le sujet "Bearing flexibility"
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OHTA, Hiroyuki, et Shoji YASUMOTO. « Ball Bearing Stiffness Incorporating Bearing Ring Flexibility. » Transactions of the Japan Society of Mechanical Engineers Series C 67, no 660 (2001) : 2643–50. http://dx.doi.org/10.1299/kikaic.67.2643.
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Jakobs, T., G. Jacobs, J. Euler, A. Rolink et J. Röder. « Impact of 3D segment profiling on friction losses of plain bearings in wind turbines main bearings ». Journal of Physics : Conference Series 2767, no 5 (1 juin 2024) : 052021. http://dx.doi.org/10.1088/1742-6596/2767/5/052021.
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Abstract Wind power is a crucial technology in transitioning to a carbon-free energy future. To increase the economic competitiveness, the levelized cost of electricity of wind power needs to be further reduced. A critical factor contributing to maintenance expenses is the failure of main rolling bearings. Replacing these rolling bearings in the case of damages is a costly procedure as it necessitates dismantling the wind turbine drivetrain. Unlike conventional rolling bearings, segmented plain bearings allow for the up-tower replacement of individual faulty segments, significantly reducing downtime and maintenance costs. The FlexPad plain bearing concept specifically addresses the need for an easy-to-maintain main bearing for wind turbines. While the current FlexPad design guideline focuses on global geometrical parameters disregarding a detailed segment profile optimization, literature suggests that a 3D-profile on the segments can enhance bearing performance by reducing frictional losses. However, the investigations conducted in literature were limited to stationary thrust bearings. The FlexPad bearing's inherent flexibility and conical shape preclude direct application of the findings in literature. Therefore, a coupled elastohydrodynamic-multi-body simulation model was developed to account for the bearing's flexibility while investigating different 3D-profiles. This study quantifies the impact 3D-profiles on friction power, solid contact, and maximum hydrodynamic pressure, demonstrating the advantages. The best 3D-profiles achieve a decrease in friction power of 18.3% with an increase of the maximum hydrodynamic pressure of just 4.9%.
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Thomsen, Kim, et Peder Klit. « Improvement of journal bearing operation at heavy misalignment using bearing flexibility and compliant liners ». Proceedings of the Institution of Mechanical Engineers, Part J : Journal of Engineering Tribology 226, no 8 (1 mars 2012) : 651–60. http://dx.doi.org/10.1177/1350650112439372.
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A flexure journal bearing design is proposed that will improve operational behaviour of a journal bearing at pronounced misalignment. Using a thermoelastohydrodynamic model, it is shown that the proposed flexure journal bearing has vastly increased the hydrodynamic performance compared to the stiff bearing when misaligned. The hydrodynamic performance is evaluated on lubricant film thickness, pressure and temperature. Furthermore, the influence of a compliant bearing liner is investigated and it is found that it increases the hydrodynamic performance when applied to a stiff bearing, whereas the liner has practically no influence on the flexure journal bearing's performance.
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Liu, Xiangyang, Rongjun Niu, Bin Wang, Shuai Zhang, Yongcun Cui et Zhanli Zhang. « Crowning Method on Bearing Supporting Large Wind Turbine Spindle Considering the Flexibility of Structure of Shaft System ». Machines 11, no 1 (26 décembre 2022) : 28. http://dx.doi.org/10.3390/machines11010028.
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To meet the precision design of bearings on large wind turbine spindles, a crowning method of bearing on wind turbine spindles considering the flexibility of the support structure is proposed. Firstly, a finite element (FE) model of the shaft system with a flexible structure is constructed by connecting the shaft and bearing through constraint equations (CE) and multi-point constraint (MPC) algorithms and replacing the bearing rollers with nonlinear spring elements and dampers. Then, the Newmark integration algorithm is used to solve the model and analyze the effect of the structure’s rigidity on the load distribution of bearings. Then, perform convergence analysis of the sequences of the spring load distribution using a high-pass filter based on fast Fourier transform (FFT) and root mean square error (RMSE) to obtain a suitable number of replacement springs. Finally, a sub-model of the upwind bearing is constructed with structured mesh. With the maximum Von Mises stress of the roller profile as the design target, the optimal logarithmic crowning of the roller and its tolerance zone under the given working conditions are obtained. The results show that the FE model of the shaft system proposed has good convergence. The FE model of the shaft system considering the flexibility of the support structure can obtain more accurate load distributions of bearings and can make the accurate crowning design of the bearing rollers based on the actual working conditions. This provides support for the precision design of bearings in large shaft systems.
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Zhang, Jun Yan, Su Fen Zhang et You Wei Zhang. « The Analysis of the Deformation and Contact Lubrication Problem of HPD Diesel Engine Connecting Rod Bearings Based on the FFT Method and Flexibility Matrix Method ». Advanced Materials Research 602-604 (décembre 2012) : 2170–73. http://dx.doi.org/10.4028/www.scientific.net/amr.602-604.2170.
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Based on the fast fourier transform (FFT) and flexibility matrix method, the effects of the FFT and flexibility matrix method on the distribution of oil film pressure, elastic deformation in the steady load and the journal center orbit of the connecting rod big-end bearings in the dynamic load are investigated. The results are shown that when the eccentricity ratio is more than 1, the maximum oil film pressure obtained by FFT method is bigger on both ends of the journal bearing and on its intermediate position is smaller. To the connecting rod big-end bearing, under the dynamic load condition, there is the same trend of the journal center orbit with two methods. However, with FFT method, the journal is largely deviated from bearing center.
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Zhang, Jun Yan, Shu Kui Han, Su Fen Zhang et You Wei Zhang. « A Comparative Study of the Methods for Calculation of Journal Bearing Elastohydrodynamic Lubrication ». Advanced Materials Research 594-597 (novembre 2012) : 2727–30. http://dx.doi.org/10.4028/www.scientific.net/amr.594-597.2727.
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Based on the fast fourier transform（FFT） and flexibility matrix method, the study is presented for journal bearing elastohydrodynamic lubrication. The effects of FFT and flexibility matrix method on the distribution of oil film pressure and elastic deformation in the steady load are investigated. The results are shown that the difficulty of the EHL for journal bearings in the case of high eccentricity ratios or heave loads can be effectively solved by the FFT method. When the eccentricity ratio is smaller, the magnitude and distribution of the oil film pressure are basic agreement by FFT method and flexibility matrix method. When the eccentricity ratio enhances, the maximum oil film pressure obtained by FFT method is bigger on both ends of the journal bearing and on its intermediate is smaller.
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Мединський, Валерій Володимирович, et Дмитро Миколайович Зінченко. « Influence of the aircraft bearing surface flexibility on its bearing properties ». Information systems, mechanics and control, no 20 (30 juin 2019) : 29–40. http://dx.doi.org/10.20535/2219-3804202019194412.
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Earles, L. L., A. B. Palazzolo et R. W. Armentrout. « A Finite Element Approach to Pad Flexibility Effects in Tilt Pad Journal Bearings : Part II—Assembled Bearing and System Analysis ». Journal of Tribology 112, no 2 (1 avril 1990) : 178–82. http://dx.doi.org/10.1115/1.2920239.
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Pad flexibility effects are studied in an actual bearing. This flexibility is shown to decrease the predicted instability onset speed of the rotor bearing system. The use of complex eigenvalue dependent bearing coefficients as compared with using synchronously reduced coefficients is seen to produce a more significant decrease in the instability onset speed. Further reductions in the instability onset speed are obtained by including pivot stiffness in the complex eigenvalue dependent bearing coefficients.
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Smolnicki, Tadeusz, et Eugeniusz Rusiński. « Superelement-Based Modeling of Load Distribution in Large-Size Slewing Bearings ». Journal of Mechanical Design 129, no 4 (29 mars 2006) : 459–63. http://dx.doi.org/10.1115/1.2437784.
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The supporting structures in large-size slewing bearings are highly flexible. In order to choose the proper bearing and shape the load-carrying structure one must estimate the distribution of forces among the individual rolling elements. Advanced numerical models are needed for this. An original method of modeling the rolling element-track system is presented and its usefulness for modeling large-size bearings is demonstrated. The results of an exemplary analysis are presented in the form of graphs and figures. The superelement-based discrete bearing models are so far most comprehensive and take into account all the phenomena involved in the bearing-supporting structures system. The application of the finite-element method and the models based on the track-rolling element-track superelement made it possible to determine the effect of the deformability of the supporting structures and the nonuniformity of their flexibility on the loading of the rolling elements in the two-row bearing. The use of formulas which do not take into account the flexibility of the supporting structures to determine the distribution of the load among the rolling elements is unacceptable.
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Kumar, D. Satish, C. Sujatha et N. Ganesan. « Disc flexibility effects in rotor bearing systems ». Computers & ; Structures 62, no 4 (février 1997) : 715–19. http://dx.doi.org/10.1016/s0045-7949(96)00214-3.
Texte intégralThèses sur le sujet "Bearing flexibility"
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Zutavern, Zachary Scott. « Fiber optic strain gauge calibration and dynamic flexibility transfer function identification in magnetic bearings ». Thesis, Texas A&M University, 2003. http://hdl.handle.net/1969.1/152.
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Historical attempts to measure forces in magnetic bearings have been unsuccessful as a result of relatively high uncertainties. Recent advances in the strain-gauge technology have provided a new method for measuring magnetic bearing forces. Fiber optic strain gauges are roughly 100 times more sensitive than conventional strain gauges and are not affected by electro-magnetic interference. At the Texas A&M Turbomachinery Laboratory, installing the fiber-optic strain gauges in magnetic bearings has produced force measurements with low uncertainties. Dynamic flexibility transfer functions exhibiting noticeable gyroscopic coupling have been identified and compared with results of a finite element model. The comparison has verified the effectiveness of using magnetic bearings as calibrated exciters in rotordynamic testing. Many applications including opportunities for testing unexplained rotordynamic phenomena are now feasible.
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Kintingu, Simion Hosea. « Design of interlocking bricks for enhanced wall construction, flexibility, alignment accuracy and load bearing ». Thesis, University of Warwick, 2009. http://wrap.warwick.ac.uk/2768/.
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The worldwide housing shortage has stimulated a search for appropriate, easy, fast and cost-effective new ways of wall construction. Among many technologies found to have promise is mortarless technology using dry-stack interlocking bricks/blocks. This thesis is about such mortarless walling technology and in particular: how to improve wall-construction flexibility, the effects of brick irregularities on wall alignment accuracy and wall behaviour (stiffness, strength) when subject to lateral forces. The flexibility of mortarless technology (MT) has been enhanced by the development of new bricks (centre-half bat and tee brick): the introduction of closer bricks led to the formation of two new bonds (patterns) namely Shokse and Lijuja bonds. It is now possible to construct more than half-brick-thick walls, to attach more than half-brickwide piers (buttresses) onto walls, and, using special bricks, to construct polygonal and curved walls using interlocking bricks. Three methods (theoretical modeling, physical experiments and computer simulation) were used to analyze the effects of brick imperfections on wall alignment accuracy. Theoretical analysis confirmed that brick moulders should concentrate on achieving parallel top and bottom faces rather than achieving true square-ness. Physical column assembly compared three brick-laying strategies namely: “random”, “reversing” and “replace”. The columns assembled using the “reversing” and “replace” strategies realized alignment improvement factors of 1.6 and 2.9 respectively over “random” strategy. The research also revealed that grooving, to prevent bricks making contact near their centre lines, improved column alignment by factor 2.13 and stiffness by factor 2.0, thus allowing construction of longer and higher walls without strengthening measures. In order to attain alignment accuracy in accordance with BS 5628-3:2005 in a dry-stack mortarless wall, this research recommends using full bricks with top and bottom surface irregularities not exceeding ±0.5mm for un-grooved bricks, and up-to ±0.9mm for grooved bricks. Further analysis was undertaken with respect to resource-use implications (cement, water, soil) of employing MT. Using MT will save 50% of wall construction cost and 50% cement consumption, which ultimately will reduce 40% of carbon emissions.
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Bedford, Adam. « Strength in flexibility : research into innovative flexible bearing designs for wave convertor permanent magnet generators ». Thesis, Lancaster University, 2011. http://clok.uclan.ac.uk/4192/.
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Originally this research was to investigate the use of hydrostatic bearings in large linear machines, such as linear generators, and determine their viability in a power generation context. It quickly became clear that it was possible to make hydro-static bearings viable, however the methods employed to do so gave rise to new possibilities which altered the scope of the research. The overall aim of the research has become to look at flexible construction, using modular generation units, as a means of creating more reliable and cost effective generators. The methods employed to do this involved modularising the generator's structure. Each module then acts as a generator in its own right transferring its power to the parent machine. The potential for each module design was assessed based on its losses, due to the bearings, and its economic potential, such as how it impacted the operation and maintenance costs or transport costs and consideration of how each design affected the power density of the parent machine. The basic structural analysis showed that, of the arrangements tried, there was a distinct advantage to restricting the number of bearings because it reduces energy losses. This is particularly true of designs that take advantage of the MMA concepts. The magnitude of the forces within the generators, during operation, lead to the creation 2-stage bearing and MMA concepts. The key reasons for them being to reducing dynamic forces within the generator and increase tolerance to design flaws and damage. Reducing the dynamic forces reduces losses in all types of bearings improving overall efficiency. Not all the concepts present in this document show commercial promise, however from the basic principles used to understand their working, there are some whose potential is clear. In general the modules have reduced the weight necessary to operate a successful generator and reduced the bearing losses no matter the type of bearing being used. Predicted force reductions mean that less strength critical and more cost effective materials can be used in the machines construction. Given that the original scope of the research was to assess a single type of bearing it has come a long way to incorporate construction methods that will reduce operation and transport costs, as well as being more efficient on some of the construction materials. The final module designs show great promise to increase the power density of generators whilst making them easy to maintain. Although hydrostatic bearings provide excellent lubrication the basic analysis performed herein shows that their energy consumption exceeds the energy loss of normal roller bearings reducing overall generator efficiency. The modular constructions presented may not provide a great jump in efficiency over previous designs however they do show a way to simplify operation and maintenance costs improving overall commercial viability. All 3D/CAD models contained herein were created by the author for this work unless otherwise stated/referenced.
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Sow, Souleymane. « Simulateur vibratoire de machines tournantes à base de machine-learning ». Electronic Thesis or Diss., Reims, 2024. http://www.theses.fr/2024REIMS038.
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Placée dans le cadre de la maintenance 4.0, cette thèse vise à développer un simulateur vibratoire pour un banc d’essais de roulements à gorges profondes, afin d’améliorer la précision des diagnostics basés sur des algorithmes de machine learning. Le travail se concentre d’abord sur l’intégration de la flexibilité des paliers dans un modèle numérique existant, créant ainsi un jumeau numérique plus représentatif des conditions réelles d’exploitation. La méthodologie s’articule autour de la conception d’un modèle numérique hybride, combinant un modèle méso (éléments discrets) et un modèle macro (éléments finis). Ces deux sous-modèles communiquent pour décrire la dynamique du système et simuler différents modes de fonctionnement. Les données générées par le simulateur sont ensuite exploitées pour mettre à jour le modèle et entraîner des algorithmes de classification (MSVM, KNN, arbres de décision), obtenant un taux de classification de 94 %. Ce résultat montre une amélioration de 10 % par rapport aux méthodes précédentes, confirmant l’efficacité de l’approche. Dans le but de mesurer l’apport qualitatif et quantitatif des données dans un diagnostic par classification, les données issues de ce modèle numérique mis à jour sont utilisées dans différentes stratégies d’hybridation de données avec les celles mesurées sur le systèmeFramed within maintenance 4.0, this thesis aims to develop a vibratory simulator for a deep-groove ball bearing test bench to improve the accuracy of diagnostics based on machine learning algorithms. The work initially focuses on integrating the flexibility of the bearing supports into an existing numerical model, thereby creating a digital twin that more accurately reflects real operating conditions. The methodology is centred around the design of a hybrid numerical model, combining a meso-model (discrete elements) and a macro-model (finite elements). These two sub-models interact to describe the system's dynamics and simulate different operating modes. The data generated by the simulator is then used to update the model and train classification algorithms (MSVM, KNN, decision trees), achieving a classification accuracy of 94%. This result demonstrates a 10% improvement compared to previous methods, confirming the approach’s effectiveness. To assess the qualitative and quantitative contributions of the data in a classification-based diagnostic, the data from the updated numerical model is used in various data hybridization strategies with those measured from the physical system
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Silva, Felipe José Passos. « Influência da deformação do encosto e do alojamento no campo de tensões em bronzinas / ». Guaratinguetá : [s.n.], 2005. http://hdl.handle.net/11449/97078.
Texte intégralRésumé :
Orientador: Fernando de Azevedo SilvaBanca: Victor Orlando Gamarra Rosado
Banca: Gustavo Aristides Santana Martínez
Resumo: Bronzinas são componentes essenciais em motores automotivos, pois são muito importantes sempre que houver peças em movimento relativo, já que sua utilização visa minimizar os danos das peças móveis mais caras e de difícil substituição. Um dos mais comuns tipos de falhas evidenciados em bronzinas é a fadiga superficial, que geralmente aparece na forma de trincas superficiais. Tensões reversas na camada do mancal podem causar fadiga superficial. Estas falhas por fadiga podem ser induzidas na superfície do mancal devido às tensões flutuantes diretas, ou na superfície de união devido às tensões flutuantes de cisalhamento. Muitas são as fontes de tensões em mancais, tais como: gradiente de pressão, flexibilidade de materiais de encosto e alojamento, presença de ranhuras de óleo, não uniformidade do apoio do alojamento, rugosidade superficial, espessura das camadas de encosto e de revestimento, problemas de montagem, entre outros. Este projeto visa determinar o campo de tensões a partir das deformações de encosto e alojamento, utilizando o método dos elementos finitos, e relacionar este campo de tensões com falhas por fadiga. Para isto, é utilizado o software comercial ANSYS® versão 7.0 no qual a bronzina é modelada.
Abstract: Journal bearings are essentials components in automotive engines, because they are very important when exist parts in relative movement, since its use aims at to minimize the damages of the more expensive and difficult substitution mobile parts. One of the most common types of evidenced failures is the surface fatigue, which it appears in the form of surface cracks. Reverse stresses in the bearing layer can cause surface fatigue. These failures can be induced in the surface due to the direct floating stresses or in the bond surface due to the shear floating stresses. There are many stress sources in bearings, such as, pressure gradient, flexibilities of backing and housing materials, presence of oil grooves, non-uniform housing supports, surface roughness, backing and covering layer thickness, assembly problems, among others. This work aims at to determine the stresses field from the backing and housing strain, using the finite elements method, and to relate this stresses field fatigue failures. For this, it is used the commercial software ANSYS® version 7.0 in which the bearing is modeled.
Mestre
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Silva, Felipe José Passos [UNESP]. « Influência da deformação do encosto e do alojamento no campo de tensões em bronzinas ». Universidade Estadual Paulista (UNESP), 2005. http://hdl.handle.net/11449/97078.
Texte intégralRésumé :
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silva_fjp_me_guara.pdf: 1797451 bytes, checksum: 8356f42bb2a95184e0bf1b4b2bb9a24f (MD5)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Universidade Estadual Paulista (UNESP)
Bronzinas são componentes essenciais em motores automotivos, pois são muito importantes sempre que houver peças em movimento relativo, já que sua utilização visa minimizar os danos das peças móveis mais caras e de difícil substituição. Um dos mais comuns tipos de falhas evidenciados em bronzinas é a fadiga superficial, que geralmente aparece na forma de trincas superficiais. Tensões reversas na camada do mancal podem causar fadiga superficial. Estas falhas por fadiga podem ser induzidas na superfície do mancal devido às tensões flutuantes diretas, ou na superfície de união devido às tensões flutuantes de cisalhamento. Muitas são as fontes de tensões em mancais, tais como: gradiente de pressão, flexibilidade de materiais de encosto e alojamento, presença de ranhuras de óleo, não uniformidade do apoio do alojamento, rugosidade superficial, espessura das camadas de encosto e de revestimento, problemas de montagem, entre outros. Este projeto visa determinar o campo de tensões a partir das deformações de encosto e alojamento, utilizando o método dos elementos finitos, e relacionar este campo de tensões com falhas por fadiga. Para isto, é utilizado o software comercial ANSYS® versão 7.0 no qual a bronzina é modelada.
Journal bearings are essentials components in automotive engines, because they are very important when exist parts in relative movement, since its use aims at to minimize the damages of the more expensive and difficult substitution mobile parts. One of the most common types of evidenced failures is the surface fatigue, which it appears in the form of surface cracks. Reverse stresses in the bearing layer can cause surface fatigue. These failures can be induced in the surface due to the direct floating stresses or in the bond surface due to the shear floating stresses. There are many stress sources in bearings, such as, pressure gradient, flexibilities of backing and housing materials, presence of oil grooves, non-uniform housing supports, surface roughness, backing and covering layer thickness, assembly problems, among others. This work aims at to determine the stresses field from the backing and housing strain, using the finite elements method, and to relate this stresses field fatigue failures. For this, it is used the commercial software ANSYS® version 7.0 in which the bearing is modeled.
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Moreira, Bruno. « Modélisation et contrôle vibratoire d'une pompe turbomoléculaire sur Paliers Magnétiques Actifs : interactions entre un contrôleur modal et la flexibilité de l'arbre et des aubages ». Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEC042.
Texte intégralRésumé :
Ce travail porte sur la modélisation et le contrôle vibratoire des pompes turbomoléculaires sur paliers magnétiques actifs (PMA). Ces pompes sont composées d'une roue aubagée multiétage accrochée à un arbre flexible. Les paliers magnétiques sont naturellement instables et nécessitent un contrôleur pour son bon fonctionnement. Dans la littérature, les simulations des rotors sur PMA sont réalisées en tenant compte d'un modèle rigide ou flexible du rotor, le plus souvent en se basant sur l'hypothèse d'axisymétrie de la partie tournante, négligeant la flexibilité des aubages et les phénomènes propres aux roues aubagées. Ces hypothèses et simplifications évitent des termes périodiques dans les équations du mouvement en boucle fermée. Néanmoins, des essais sur une pompe en fonctionnement ont montré une corrélation entre la dynamique du contrôleur et la réponse des aubages.L'objectif de cette thèse est donc de pouvoir évaluer la dynamique du modèle mécanique complet sur paliers magnétiques actifs, mettant l'accent sur les effets de la flexibilité de l'arbre et des aubages et leur interaction avec le contrôleur. Pour cela, un modèle analytique de l'arbre et de la roue aubagée a été obtenu à partir de la méthode de Rayleigh-Ritz. Ce modèle prend en compte les effets gyroscopiques, d'assouplissement et rigidification centrifuges et le désaccordage des aubes. Une loi de contrôle modal prenant en compte les modes rigides a été mise en œuvre, associée à des filtres du second ordre pour amortir le mode flexible d'arbre. Finalement, un compensateur gyroscopique limite les variations des pulsations propres du système avec la vitesse de rotation. Les simulations ont été faites en trois étapes. La première étape consistait à étudier le comportement en boucle ouverte de la pompe. Dans cette phase de l'étude, les simulations du modèle mécanique obtenu considéraient les paliers linéaires et se focalisait sur les effets du désaccordage des aubes et du couplage avec l'arbre flexible. Les résultats numériques obtenus corrèlent bien avec les mesures réalisées sur une pompe en fonctionnement. La deuxième étape a été d'évaluer les performances de la loi de contrôle proposée sur un modèle axisymétrique, et tout particulièrement de garantir la stabilité en boucle fermée de notre contrôleur. Finalement les deux approches initiales ont été combinées pour simuler le système mécanique complet en boucle fermée avec une loi de contrôle. Les résultats suggèrent que la perte de symétrie associée au mouvement flexible des aubages peut engendrer des instabilités non-prévues par l'étude d'un modèle axisymétrique de la pompe. Les résultats obtenus durant cette thèse montrent l'importance de la prise en compte de la dynamique des aubages sur les analyses de performance du contrôleurAbstractThe subject of this work is mechanical modeling and vibration control of a turbomolecular pump on active magnetic bearings. Such pumps are composed of a multistage bladed disk attached to a flexible shaft. Magnetic bearings are naturally unstable and need a controller for proper operation. In the literature, magnetic suspended rotating systems simulations are performed taking into account a rigid or flexible rotor model, mostly based on the axisymmetric assumption of the rotating part, neglecting blades flexibility and all related phenomena. This avoids periodic terms in closed loop motion equations. Nevertheless, tests on an operating pump highlight a strong coupling between blades motion and controller dynamics.The objective of this work is to evaluate the dynamics of the complete mechanical model on active magnetic bearings, emphasising the effects of shaft and blades flexibility as well as its interaction with the controller. On that purpose, an analytical model was obtained using Rayleigh-Ritz method. This model takes into account gyroscopic effects, spin softening, centrifugal stiffening and blades mistuning. A modal control law taking into account the rigid modes has been implemented, associated with second order filters to dampen shaft flexural mode. Finally, a gyroscopic compensator limits eigenvalues dependence on spin speed.Simulations and analysis were tackled in three steps. The first one was to study the open-loop behavior of the pump. In this phase, bearings were considered as linear springs, focusing the analysis on the effects of blades mistuning and coupling of shaft and blades flexural motion in rotation. Numerical results correlate well with results from a pump in operation. Second step consisted on evaluating the proposed control law performance and closed loop stability on an axisymmetric model. Finally the two initial approaches were combined to simulate the complete mechanical system including magnetic bearings and control law. Results suggest that the loss of symmetry associated with blades motion may cause instabilities which are not foreseen by an axisymmetric model. The developed model highlights the importance of taking into account the dynamics of the blades on the synthesis and analysis of magnetic bearing controllers
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Wang, Fu Zhou, et 王富洲. « Rigid model-based feedback linearization and fuzzy composite control for magnetic bearings including rotor eccentricity and flexibility ». Thesis, 1996. http://ndltd.ncl.edu.tw/handle/70882258254447473557.
Texte intégralLivres sur le sujet "Bearing flexibility"
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Modeling of rolling element bearing mechanics--computer program updates. MSFC, Ala : National Aeronautics and Space Administration, Marshall Space Flight Center, 1997.
Trouver le texte intégralChapitres de livres sur le sujet "Bearing flexibility"
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Krishan, A. L., V. I. Rimshin, I. L. Shubin, M. A. Astafeva et A. A. Stupak. « Compressed Reinforced Concrete Elements Bearing Capacity of Various Flexibility ». Dans Lecture Notes in Civil Engineering, 283–91. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-85236-8_26.
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Phadatare, Hanmant P., Sankalp Singh et Barun Pratiher. « Effect of Unbalance with Bearing Flexibility on Vibration Phenomenon of Geometrically Nonlinear Rotating Shaft with Ball Bearing ». Dans Lecture Notes in Mechanical Engineering, 1261–76. Singapore : Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-16-0550-5_120.
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Heras, Iker, Josu Aguirrebeitia, Mikel Abasolo et Ibai Coria. « Load Distribution in Four-Point Contact Slewing Bearings Considering Manufacturing Errors and Ring Flexibility ». Dans EuCoMeS 2018, 267–74. Cham : Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-98020-1_31.
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Moreira, Alysson B. Barbosa, et Fabrice Thouverez. « Dynamic Modelling and Vibration Control of a Turbomolecular Pump with Magnetic Bearings in the Presence of Blade Flexibility ». Dans Rotating Machinery, Vibro-Acoustics & ; Laser Vibrometry, Volume 7, 101–10. Cham : Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-74693-7_10.
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Shi, Zhifeng, Lan Luo, Gang Zhang, Changfeng Yan et Jing Liu. « Effects of Cage Flexibility and Crack Propagation on Roller-Cage Pocket Interaction Forces and Dynamics in Cylindrical Roller Bearings ». Dans Mechanisms and Machine Science, 34–47. Cham : Springer Nature Switzerland, 2024. http://dx.doi.org/10.1007/978-3-031-69483-7_4.
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Chung, Heejung. « The flexibility paradox : why more freedom at work leads to more work ». Dans The Flexibility Paradox, 69–84. Policy Press, 2022. http://dx.doi.org/10.1332/policypress/9781447354772.003.0005.
Texte intégralRésumé :
This chapter provides the theoretical underpinning of the flexibility paradox and the resulting self-exploitation. This chapter first summarises the ideas of previous scholars– for example the theories of social exchange, enforced intensification, and enabled intensification, entreployee, entrepreneurial self, and the theory of autonomy-control paradox. This chapter draws from Foucault’s theories of homo-economicus and the subjectification of self to provide a broader framework of understanding the flexibility paradox. More specifically, it argues that we now live in a society where all interactions takes form of economic exchanges, where workers internalise these ideas of capitalism. In this context, “freedom” over one’s work is more likely to lead to workers working longer and harder, because the failure to do so will only result in the worker themselves bearing the associated risk of income insecurity, unemployment or loss of position within the organisation/labour market. This chapter also examines whether this phenomenon in on the rise especially with the millennial (and zennial) generation, who have been born into the world of gig-economy and the demise of the collective. Finally, the chapter explore some of the key indicators of such societal change by exploring the idea and data around work-centrality and passion at work.
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Hayes, Christine. « The Flexibility of Torah ». Dans What's Divine about Divine Law ? Princeton University Press, 2015. http://dx.doi.org/10.23943/princeton/9780691165196.003.0011.
Texte intégralRésumé :
This chapter examines sources that shed light on a variety of issues bearing on the question of the flexibility of the divine law of Israel according to the talmudic rabbis. In many of these sources, the Law is seen to be susceptible to change through rational adjustments by humans. The rhetoric surrounding human adjustment of the Law varies. In some passages these adjustments are represented as a kind of natural evolution justified by values and commitments internal to the system. In some passages, however, they are represented as interventions based on values and commitments external to the system, raising important questions about the agency and authority of human beings in a system of divine law. On what grounds do humans modify the Law? How is it that rational modification of the Law and the implied fallibility of the divine lawgiver do not impinge upon the Law's divinity in the eyes of the rabbis?
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Barry, M. K., I. L. Al-Qadi, H. Ozer et F. Safi. « An implementation of the Illinois flexibility index testing protocol for balanced asphalt mix designs ». Dans Bearing Capacity of Roads, Railways and Airfields, 217–21. CRC Press, 2017. http://dx.doi.org/10.1201/9781315100333-28.
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Chesnais, Jean-Claude. « Introduction : The ‘Theory’ of Demographic Transition : Its Conciseness, Diversity, and Flexibility ». Dans The Demographic Transition, 1–9. Oxford University PressOxford, 1992. http://dx.doi.org/10.1093/oso/9780198286592.003.0001.
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Abstract Demography is a science in which general theories are rare. Aside from Malthus’s theory, which emphasizes constraints of subsistence on population, as a principal body of thought there is only what is called by convention the theory of demographic transition. The most important point of comparison between these two explanatory systems lies in the supposed effect of economic development on fertility. In the Malthusian view, economic development stimulates fertility, the increase in demand for work encouraging marriage and family formation. In the transitional view, the relation between industrialization and fertility is inverse: industrial revolution raises the standard of living and stimulates, especially, a general aspiration towards an always greater degree of comfort, which, in turn, promotes the limitation of child-bearing.
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Kamali, Mohammad Hashim. « Conclusion and Recommendations ». Dans Crime and Punishment in Islamic Law, 334–46. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780190910648.003.0034.
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While bearing in mind the diversity of practices and developments concerning Islamic criminal laws in Muslim countries, as well as the strong currents of opinion that obtain on ḥudūd, the presentation in this chapter offers a number of reform proposals on each of the ḥudūd offences, qiṣāṣ, and taʿzīr. These proposals integrate a degree of flexibility and choice that envisage different possibilities for various countries and jurisdictions. These proposals do not preclude the suspension altogether of at least some ḥudūd penalties.
Actes de conférences sur le sujet "Bearing flexibility"
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Schank, Troy, et Kynn Schulte. « A Smart Position Sensor for Articulated Rotors ». Dans Vertical Flight Society 71st Annual Forum & Technology Display, 1–10. The Vertical Flight Society, 2015. http://dx.doi.org/10.4050/f-0071-2015-10190.
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Modern articulated rotors utilize an elastomeric bearing on the root of each blade to allow multi-axis articulation through a single component. The bearing forms a spherical joint that makes measuring angular displacements in specific blade axes both coupled and difficult to measure. A smart sensing concept is developed to uncouple and separately measure the blade flapping, feathering, and lead-lag position. The sensor concept projects a magnetic field from the blade root to the rotor hub such that flap, lag and pitch displacements can be derived from a hub mounted pickup array. The device utilizes permanent magnets on the blade root and an array of Anisotropic Magnetoresitive (AMR) sensors on the hub. The sensor array is integrated with other electronic components, including a microprocessor in a printed circuit board, forming a self contained sensing system. The 'smart' sensor is software driven, self checking, and can be networked with other sensors for application flexibility. The sensor accuracy is ensured through a process that develops calibration coefficients that are loaded into system non-volatile memory. The sensor system is designed for initial application on an articulated tail rotor for flight test purposes. Risk reduction testing is conducted in simulated tail rotor environmental conditions including vibration and shock, elevated centrifugal force (CF), temperature extremes and electromagnetic emissions / susceptibility. All development and test results indicate the new sensor technology is valid and ready for use in its initial flight test application.
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Gaines, Jennifer E., et Dara W. Childs. « The Impact of Pad Flexibility on the Rotordynamic Coefficients of Tilting-Pad Journal Bearings ». Dans ASME Turbo Expo 2015 : Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-42289.
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Static and dynamic load tests were performed on a three-pad, rocker-pivot, tilting-pad journal bearing (TPJB) with three interchangeable pad configurations, each with measurably different pad flexibilities. Measured dynamic-stiffness data for the bearing were readily fitted by a frequency-independent, constant-coefficient [K][C][M] model. The test bearing had a 101 .74 mm diameter with L/D = 0.6 Tests were conducted over the speed range of 6 to 12 krpm, with unit loads varying from .172 to 1.724 MPa. An ISO VG 46 lubricant was used as the test fluid. Pad flexibility was characterized as the change in the pad’s bending stiffness or the change in pad thickness. A finite-element model was created to predict the structural bending stiffness of each pad configuration, showing a significant pad-flexibility increase as pad thickness decreased. To examine the effect of pad flexibility on the rotordynamic coefficients, the measured results were compared across pad configurations and showed that the pad-flexibility increase reduced the direct damping coefficients by 12–20%. As pad flexibility increased, the direct stiffness coefficients could increase or decrease, depending on the unit load. They varied from an increase of 12% at low unit loads to a decrease of 3% at high unit loads. Results show that the pad’s structural bending stiffness or flexibility is important when predicting the bearing’s dynamic performance. Damping is consistently over-predicted when neglecting pad flexibility. A non-dimensional pad flexibility parameter αflex was developed. It related the average deflection across the pad surface to the pad’s arc length and was to relate the pad flexibility of multiple bearings of different sizes. A bearing code was used to predict the percent change in direct damping coefficients for rigid-pad/flexible-pivot and flexible-pad/flexible-pivot models for a surface speed of 54 m/s and a unit load of 783 kPa for the three pad configurations tested here plus five additional tested bearings from the literature. For the minimum-pad-thickness configuration tested here, the code predicted a 20% drop in predicted Cxx (off-load-axis direct damping) when comparing a model that included pad flexibility with a model that neglected pad flexibility. In terms of αflex, the two thinnest pad configurations tested here are quite flexible compared to both TPJB’s pads used in industry and previously-tested TPJB pads.
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Jiale, Tian, Yu Lie et Zhou Jian. « Frequency Effects on Dynamic Characteristics of Tilting-Pad Journal Bearings due to Pivot Flexibility ». Dans ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-70681.
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The stable working condition of high speed, heavy loaded rotating machinery depends strongly on the stability provided by the journal bearing. Tilting pad journal bearings (TPJB) are widely used under such situation due to their inherent stability performance. However, because of the complexity of the TPJB structure, obtaining a reliable prediction of the journal bearing’s dynamic characteristics has always been a challenging task. In this paper, a theoretical analysis has been done to investigate the dynamic performance of a 4 pad TPJB with ball-in-socket pivot, emphasizing on the frequency dependency due to pivot flexibility. The analytical model containing the complete set of dynamic coefficients of the TPJB is built and the pivot stiffness is calculated and used to evaluate the equivalent dynamic coefficients of the bearing. In general, at lower perturbation frequency, the equivalent stiffness and damping increase with frequency. While for higher perturbation frequency, the dynamic coefficients are nearly independent of the frequency. Moreover, the results also show the limit value of the dynamic characteristics of the TPJB when the perturbation frequency is set to 0+ and ∞.
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Gu¨rkan, N. Ersan, et H. Nevzat O¨zgu¨ven. « Interactions Between Backlash and Bearing Clearance Nonlinearity in Geared Flexible Rotors ». Dans ASME 2007 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/detc2007-34101.
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In this study, the interactions between backlash, bearing clearance and bearing flexibility are studied in geared flexible rotors. For this purpose, the non-linear mathematical model developed in a recent previous study for geared rotors on flexible bearings is extended further to handle clearance nonlinearity in bearings. The model consists of elastic shafts on elastic bearings with clearance, and coupled by a non-linear gear mesh interface. Shafts are modeled by using finite elements. The mathematical model includes the axial loading on shafts, rotary inertia, material damping of shafts, backlash nonlinearity of gear mesh and flexible bearings with clearances nonlinearity. The model considers also the effects of gear errors and profile modifications. The excitation effect of time varying mesh stiffness is indirectly included into the analysis through a periodic displacement representing loaded static transmission error (STE). STE input is modeled by the highest n harmonic terms of the Fourier series representation of the measured or calculated data. The model developed is believed to be one of the most advanced ones: It includes several linear and non-linear effects and capable of handling various different gear-rotor-bearing configurations. Through several case studies, the combined effects of backlash, bearing clearance, and bearing flexibility on dynamic mesh force and bearing loads are studied.
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Yu, Bo, Endian Xu, Kai Wang, Xinyuan Wang et Lihua Yang. « Performance Analysis of Tilting Pad Journal Bearing Considering Base Flexibility ». Dans 2022 Global Reliability and Prognostics and Health Management (PHM-Yantai). IEEE, 2022. http://dx.doi.org/10.1109/phm-yantai55411.2022.9942146.
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San Andrés, Luis, et Yingkun Li. « Effect of Pad Flexibility on the Performance of Tilting Pad Journal Bearings : Benchmarking a Predictive Model ». Dans ASME Turbo Expo 2015 : Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-42776.
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Tilting pad journal bearings (TPJBs) supporting high performance turbomachinery rotors have undergone steady design improvements to satisfy ever stringent operating conditions that include large specific loads due to smaller footprints, and high surface speeds that promote flow turbulence and thus larger drag power losses. Simultaneously, predictive models continuously evolve to include minute details on bearing geometry, pads and pivots’ configurations, oil delivery systems, etc. In general, predicted TPJB rotordynamic force coefficients correlate well with experimental data for operation with small to moderately large unit loads (1.7 MPa). Experiments also demonstrate bearing dynamic stiffnesses are frequency dependent, best fitted with a stiffness-mass like model whereas damping coefficients are adequately represented as of viscous type. However, for operation with large specific loads (> 1.7 MPa), poor correlation of predictions to measured force coefficients is common. Recently, an experimental effort [1] produced test data for three TPJB sets, each having three pads of unequal thickness, to quantify the effect of pad flexibility on the bearings’ force coefficients, in particular damping, over a range of load and rotational speed conditions. This paper introduces a fluid film flow model accounting for both pivot and pad flexibility to predict the bearing journal eccentricity, drag power loss, lubricant temperature rise and force coefficients of typical TPJBs. A finite element pad structural model including the Babbitt layer is coupled to the thin film flow model to determine the mechanical deformation of the pad surface. Predictions correlate favorably with test data, also demonstrating that pad flexibility produces a reduction of up to 34% in damping for the bearing with the thinnest pads relative to that with the thickest pads. A parametric study follows to quantify the influence of pad thickness on the rotordynamic force coefficients of a sample TPJB with three pads of increasing preload, rp = 0, 0.25 (baseline) and 0.5. The bearing pads are either rigid or flexible by varying their thickness. For design considerations, dimensionless static and dynamic characteristics of the bearings are presented versus the Sommerfeld number (S). Pad flexibility shows a more pronounced effect on the journal eccentricity and the force coefficients of a TPJB with null pad preload than for the bearings with larger pad preloads (0.25 and 0.5), in particular for operation with a small load or at a high surface speed (S>0.8).
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Andreau, C., F. Ferdi, R. Ville et M. Fillon. « A Method for Determination of Elastohydrodynamic Behavior of Line Shafting Bearings in Their Environment ». Dans ASME/STLE 2007 International Joint Tribology Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/ijtc2007-44056.
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Safe operation of a rotating line shafting needs to use proper tools and methodology for an accurate determination of its static and steady state behavior in running conditions. Taking into account properly the characteristics of shaft environment is of primary importance. These characteristics are mainly bearing material behavior, oil film dynamic coefficients (stiffness and damping), flexibility and deformations of structure supporting line shafting bearings. Global non linear behavior of the entire system needs to be analyzed to get an accurate solution, as oil film dynamic coefficients depend on steady state location of shaft inside the considered bearing, which depends itself on oil film stiffness, and also on flexibility and deformations of supporting structure. Calculations of structure flexibility and deformations, as well as line shafting stiffness characteristics are performed straightforwardly using finite element method. Solving global matrix equilibrium equation needs to solve elastohydrodynamic (EHD) problem on each bearing. A specific finite element method is developed for this purpose. This method is attractive for taking into account thick and flexible bearing materials such as multi layer synthetic materials. It can also support further developments (effects of geometry defects on bearings, solving thermoelastohydrodynamic problem). The application of the method to the propulsion line shafting of a large LNGC ship (Liquid Natural Gas Carrier) is presented, the final target being the determination of the most optimum bearing offsets for operating safely the vessel in all relevant conditions.
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Bahan, Doğancan, et Ender Ciğeroğlu. « Nonlinear Dynamic Analysis of an Asymmetric Ball Bearing Rotor System ». Dans ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-12218.
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Abstract Performance of ball bearing–rotor systems are highly dependent on and often limited by characteristics of ball bearings. Several studies are available in the literature, investigating varying compliance and subharmonic resonances of ball bearings. Most of the studies are carried out with rigid rotors to focus on modelling of the bearings. There exist few studies which take flexibility of rotors into account. Furthermore, even if the rotor flexibility is modelled, most of the time symmetrical rotors are considered. However, rotors are rarely symmetric in realistic applications due to different locations of bearings and different weights of rotor components (compressors, turbines etc.). In this study, an asymmetric, balanced, flexible rotor supported by ball bearings considering Hertzian contact and radial clearance is investigated. Rotor shaft is modelled with Nelson finite rotor elements using Timoshenko beam theory and disks are considered as rigid masses. Harmonic Balance Method (HBM) is used to obtain nonlinear algebraic equations in the frequency domain and Alternating Frequency Time (AFT) method is utilized to find Fourier coefficients of nonlinear bearing forces. In order to decrease the number of nonlinear equations to be solved, Receptance Method (RM) is applied. Resulting set of nonlinear algebraic equations is solved by using Newton’s method with arclength continuation. Several case studies are performed and effects of asymmetry on nonlinear periodic vibration response of rotors are studied.
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Dmochowski, Waldemar. « Dynamic Properties of Tilting-Pad Journal Bearings : Experimental and Theoretical Investigation of Frequency Effects Due to Pivot Flexibility ». Dans ASME Turbo Expo 2006 : Power for Land, Sea, and Air. ASMEDC, 2006. http://dx.doi.org/10.1115/gt2006-90280.
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Tilting-pad journal bearings (TPJB) dominate as rotor supports in high speed rotating machinery. The paper analyzes frequency effects on the TPJB’s stiffness and damping characteristics based on experimental and theoretical investigations. The experimental investigation has been carried out on a five pad tilting-pad journal bearing of 98 mm in diameter. Time domain and multifrequency excitation has been used to evaluate the dynamic coefficients. The calculated results have been obtained from a three-dimensional computer model of TPJB, which accounts for thermal effects, turbulent oil flow, and elastic effects, including that of pad flexibility. The analyzes of the TPJB’s stiffness and damping properties showed that the frequency effects on the bearing dynamic properties depend on the operating conditions and bearing design. It has been concluded that the pad inertia and pivot flexibility are behind the variations of the stiffness and damping properties with frequency of excitation.
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Neisi, Neda, Eerik Sikanen, Janne E. Heikkinen et Jussi Sopanen. « Stress Analysis of a Touchdown Bearing Having an Artificial Crack ». Dans ASME 2017 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/detc2017-67750.
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The active magnetic bearings (AMBs) are often the preferred bearing solution in high speed rotating machines. Even though AMBs have numerous advantages in comparison to normal bearings they are sensitive to the power shutdowns. In the absence of electromagnetic field, the rotor collides with touchdown bearing. The high contact forces occurring between the rotor and touchdown bearing might lead to a contact surface failure in the touchdown bearings. In this study, the simulation model has been used to study the stresses of the touchdown bearing with an artificial crack. Flexibility of the rotor is modelled using the finite element method and frictional contacts are defined between the rotor and touchdown bearing. Hertzian contact theory is used to model all internal contacts in the ball bearing type touchdown bearings. This makes it possible to obtain the Hertzian contact stresses in each ball of the touchdown bearing and evaluate the stress intensity factors for a crack propagation analysis. The results show that increase in the dynamic friction coefficient between the rotor and bearing as well as increase in the air gap leads to a higher maximum Hertzian stress. As a result of the higher contact stress the stress intensity factor will increase.
Rapports d'organisations sur le sujet "Bearing flexibility"
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Kinser, Ryan, Mark Barkey, Timothy Rushing, Abby Cisko, Lyan Garcia, Paul Allison et J. Jordon. Computationally efficient modeling of lightweight expeditionary airfield surfacing systems at large length scales. Engineer Research and Development Center (U.S.), février 2024. http://dx.doi.org/10.21079/11681/48266.
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Expeditionary airfield matting systems are lightweight, portable surfaces that enable the rapid deployment of infrastructure to support aircraft operations. Individual matting components are assembled via interlocking joints to construct arrays that serve as temporary aircraft operating surfaces. The paper outlines the homogenization of the AM2 portable airfield matting system and its interlocking mechanisms to permit computationally efficient analyses toward understanding mechanisms that influence the global behavior of these arrays and underlying subgrade during aircraft maneuvers. An equivalent orthotropic two-dimensional continuum was developed from finite element analysis of a detailed three-dimensional model and its flexural behavior was validated against experimental data and solid finite element models. Interlocking joints were characterized using node-to-node connector elements based on subscale finite element studies. Both components were implemented into a full-scale model representative of a typical test section, and responses to static high tire pressure aircraft loads were analyzed over a soil foundation representing a California bearing ratio of 6%, yielding promising agreement with experimental data. Results of this study reveal an inherent coupling between load transfer, mat deflection, and near-surface subgrade stress with dependence on tire location, mat core shear flexibility, and joint stiffness.
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Delmer, Deborah, Nicholas Carpita et Abraham Marcus. Induced Plant Cell Wall Modifications : Use of Plant Cells with Altered Walls to Study Wall Structure, Growth and Potential for Genetic Modification. United States Department of Agriculture, mai 1995. http://dx.doi.org/10.32747/1995.7613021.bard.
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Our previous work indicated that suspension-cultured plant cells show remarkable flexibility in altering cell wall structure in response either to growth on saline medium or in the presence of the cellulose synthesis inhibitor 2,-6-dichlorobenzonitrile (DCB). We have continued to analyze the structure of these modified cell walls to understand how the changes modify wall strength, porosity, and ability to expand. The major load-bearing network in the walls of DCB-adapted dicot cells that lack a substantial cellulose-xyloglucan network is comprised of Ca2+-bridged pectates; these cells also have an unusual and abundant soluble pectic fraction. By contrast, DCB-adapted barley, a graminaceous monocot achieves extra wall strength by enhanced cross-linking of its non-cellulosic polysaccharide network via phenolic residues. Our results have also shed new light on normal wall stucture: 1) the cellulose-xyloglucan network may be independent of other wall networks in dicot primary walls and accounts for about 70% of the total wall strength; 2) the pectic network in dicot walls is the primary determinant of wall porosity; 3) both wall strength and porosity in graminaceous monocot primary walls is greatly influenced by the degree of phenolic cross-linking between non-cellulosic polysaccharides; and 4) the fact that the monocot cells do not secrete excess glucuronoarabinoxylan and mixed-linked glucan in response to growth on DCB, suggests that these two non-cellulosic polymers do not normally interact with cellulose in a manner similar to xyloglucan. We also attempted to understand the factors which limit cell expansion during growth of cells in saline medium. Analyses of hydrolytic enzyme activities suggest that xyloglucan metabolism is not repressed during growth on NaCl. Unlike non-adapted cells, salt-adapted cells were found to lack pectin methyl esterase, but it is not clear how this difference could relate to alterations in wall expansibility. Salt-adaped cell walls contain reduced hyp and secrete two unique PRPP-related proteins suggesting that high NaCl inhibits the cross-linking of these proteins into the walls, a finding that might relate to their altered expansibility.
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Moghimi, Gholamreza, et Nicos Makris. Response Modification of Structures with Supplemental Rotational Inertia. Pacific Earthquake Engineering Research Center, University of California, Berkeley, CA, janvier 2024. http://dx.doi.org/10.55461/tihv1701.
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Tall, multistory, buildings are becoming increasingly popular in large cities as a result of growing urbanization trends (United Nations Department of Economic and Social Affairs 2018). As cities continue to grow, many of them along the coasts of continents which are prone to natural hazards, the performance of tall, flexible buildings when subjected to natural hazards is a pressing issue with engineering relevance. The performance of structures when subjected to dynamic loads can be enhanced with various response modification strategies which have been traditionally achieved with added stiffness, flexibility, damping and strength (Kelly et al. 1972; Skinner et al. 1973, 1974; Clough and Penzien 1975; Zhang et al. 1989; Aiken 1990; Whittaker et al. 1991; Makris et al. 1993a,b; Skinner et al. 1993; Inaudi and Makris 1996; Kelly 1997; Soong and Dargush 1997; Constantinou et al. 1998; Makris and Chang 2000a; Chang and Makris 2000; Black et al. 2002, 2003; Symans et al. 2008; Sarlis et al. 2013; Tena-Colunga 1997). Together with the elastic spring that produces a force proportional to the relative displacement of its end-nodes and the viscous dashpot that produces a force proportional to the relative velocity of its end-nodes; the inerter produces a force proportional to the relative acceleration of its end-nodes and emerges as the third elementary mechanical element (in addition to the spring and dashpot) capable for modifying structural response. Accordingly, in this report we examine the seismic performance of multistory and seismically isolated structures when equipped with inerters. In view that the inerter emerges as the third elementary mechanical element for the synthesis of mechanical networks, in Chapter 2 we derive the basic frequency- and time-response functions of the inerter together with these of the two-parameter inertoelastic and inertoviscous mechanical networks. Chapter 3 examines the response of a two-degree-of-freedom (2DOF) structure where the first story is equipped with inerters. Both cases of a stiff and a compliant support of the inerters are examined. The case of two parallel clutching inerters is investigated and the study concludes that as the compliance of the frame that supports the inerters increases, the use of a single inerter offers more favorable response other than increasing the force transferred to the support frame. Chapter 4 examines the seismic response analysis of the classical two-degree-of-freedom isolated structure with supplemental rotational inertia (inerter) in its isolation system. The analysis shows that for the “critical” amount of rotational inertia which eliminates the participation of the second mode, the effect of this elimination is marginal on the structural response since the participation of the second mode is invariably small even when isolation systems without inerters are used. Our study, upon showing that the reaction force at the support of the inerter is appreciable, proceeds with a non-linear response analysis that implements a state-space formulation which accounts for the bilinear behavior of practical isolation system (single concave sliding bearings or lead-rubber bearings) in association with the compliance of the support of the inerter. Our study concludes that supplemental rotational inertia aggravates the displacement and acceleration response of the elastic superstructure and as a result, for larger isolation periods (Tb > 2.5s) the use of inerters in isolation systems is not recommended. Chapter 5 first examines the response analysis of a SDOF elastoplastic and bilinear structure and reveals that when the yielding structure is equipped with supplemental rotational inertia, the equal- displacement rule is valid starting from lower values of the pre-yielding period given that the presence of inerters lengthens the apparent pre-yielding period. The analysis concludes that sup- plemental rotational inertia emerges as an attractive response modification strategy for elastoplastic and bilinear SDOF structures with pre-yielding periods up to T1 = 1.5sec. For larger pre-yielding periods (say T1 > 2.0sec), the effectiveness of inerters to suppress the inelastic response of 2DOF yielding structures reduces; and for very flexible first stories; as in the case of isolated structures examined in chapter 4, the use of inerter at the first level (isolation system) is not recommended. Finally, chapter 6 shows that, in spite of the reduced role of inerters when placed at floor levels other than the first level (they no-longer suppress the induced ground acceleration nor they can eliminate the participation of higher modes), they still manifest a unique role since it is not possible to replace a structure with solitary inerters at higher levels with an equivalent traditional structure without inerters.