The Experts below are selected from a list of 189 Experts worldwide ranked by ideXlab platform
Hassan Shirvani - One of the best experts on this subject based on the ideXlab platform.
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An analytical approach for analysis and optimisation of slider bearings with infinite width parallel textures
Tribology International, 2010Co-Authors: Ramin Rahmani, Ayoub Shirvani, Iraj Mirzaee, Hassan ShirvaniAbstract:Abstract This paper introduces an analytical approach to study the textured surfaces in hydrodynamic lubrication regime. For this purpose, a method of integrating the Reynolds equation for slider bearings with surface discontinuities is presented. By introducing appropriate dimensionless parameters, analytical relations for various texture profiles in both indented and projected forms are delivered. These relations express the nature of mathematical dependence between textured bearing performance measures and geometrical/operational parameters. An optimisation procedure is employed to achieve the optimum texturing parameters promoting maximum load capacity, load capacity to Lubricant Flow Rate ratio and minimum friction coefficient for asymmetric partially textured slider bearings.
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Analytical analysis and optimisation of the Rayleigh step slider bearing
Tribology International, 2009Co-Authors: Ramin Rahmani, Ayoub Shirvani, Hassan ShirvaniAbstract:In tribology, the Rayleigh step is known as a bearing with the highest load capacity amongst all other possible bearing geometries. In classical resources on tribology, it is also shown that there is an optimum geometry for the Rayleigh step providing the highest load capacity. However, the analyses are confined to a special case where the effect of hydrostatic pressure is neglected. Furthermore, the possible optimum parameters in terms of the friction force and/or friction coefficient as well as the Lubricant Flow Rate have not been discussed. In this study, the Rayleigh step is comprehensively analysed including the effect of variations of pressure at the boundaries on the optimum parameters. In addition, the bearing is also optimised considering Lubricant Flow Rate, friction force and friction coefficient. It is shown that the optimum bearing parameters are strictly dependent on the variations of the pressure at the boundaries. It is also verified that the optimum point(s) in terms of load capacity are not necessarily equal to the optimum point(s) considering friction coefficient and/or Lubricant Flow Rate even though if there is no pressure difference between bearing endings.
Paolo Pennacchi - One of the best experts on this subject based on the ideXlab platform.
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Ball bearing skidding and over-skidding in large-scale angular contact ball bearings: Nonlinear dynamic model with thermal effects and experimental results
Mechanical Systems and Signal Processing, 2021Co-Authors: Shuai Gao, Steven Chatterton, Lorenzo Naldi, Paolo PennacchiAbstract:Abstract 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.
Ramin Rahmani - One of the best experts on this subject based on the ideXlab platform.
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An analytical approach for analysis and optimisation of slider bearings with infinite width parallel textures
Tribology International, 2010Co-Authors: Ramin Rahmani, Ayoub Shirvani, Iraj Mirzaee, Hassan ShirvaniAbstract:Abstract This paper introduces an analytical approach to study the textured surfaces in hydrodynamic lubrication regime. For this purpose, a method of integrating the Reynolds equation for slider bearings with surface discontinuities is presented. By introducing appropriate dimensionless parameters, analytical relations for various texture profiles in both indented and projected forms are delivered. These relations express the nature of mathematical dependence between textured bearing performance measures and geometrical/operational parameters. An optimisation procedure is employed to achieve the optimum texturing parameters promoting maximum load capacity, load capacity to Lubricant Flow Rate ratio and minimum friction coefficient for asymmetric partially textured slider bearings.
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Analytical analysis and optimisation of the Rayleigh step slider bearing
Tribology International, 2009Co-Authors: Ramin Rahmani, Ayoub Shirvani, Hassan ShirvaniAbstract:In tribology, the Rayleigh step is known as a bearing with the highest load capacity amongst all other possible bearing geometries. In classical resources on tribology, it is also shown that there is an optimum geometry for the Rayleigh step providing the highest load capacity. However, the analyses are confined to a special case where the effect of hydrostatic pressure is neglected. Furthermore, the possible optimum parameters in terms of the friction force and/or friction coefficient as well as the Lubricant Flow Rate have not been discussed. In this study, the Rayleigh step is comprehensively analysed including the effect of variations of pressure at the boundaries on the optimum parameters. In addition, the bearing is also optimised considering Lubricant Flow Rate, friction force and friction coefficient. It is shown that the optimum bearing parameters are strictly dependent on the variations of the pressure at the boundaries. It is also verified that the optimum point(s) in terms of load capacity are not necessarily equal to the optimum point(s) considering friction coefficient and/or Lubricant Flow Rate even though if there is no pressure difference between bearing endings.
Karl Wygant - One of the best experts on this subject based on the ideXlab platform.
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On the Predicted Effect of Angular Misalignment on the Performance of Oil Lubricated Thrust Collars in Integrally Geared Compressors
Journal of Engineering for Gas Turbines and Power, 2016Co-Authors: Travis A. Cable, Luis San Andrés, Karl WygantAbstract:Multiple-stage integrally geared compressors (IGCs) offer improved thermal efficiency and easier access for maintenance and overhaul than single-shaft centrifugal compressors. In an IGC, a main bull shaft drives pinion shafts, each having an impeller at its ends. The compression of process gas in the compressor stages induces axial loads along the pinion shafts that are transmitted via thrust collars (TCs) to the main bull gear (BG) shaft and balanced by a single thrust bearing. Manufacturing inaccuracies and a poor assembly process can lead to static angular misalignments of the TC and BG surfaces that affect the operating film thickness as well as the force and reaction moments of the lubricated mechanical element. In a follow-up to San Andrés et al. (2015, “On the Predicted Performance of Oil Lubricated Thrust Collars in Integrally Geared Compressors,” ASME J. Eng. Gas Turbines Power, 137(5), pp. 1–9), this paper presents an investigation of the performance of a single thrust collar configuration operating with increasing static angular misalignment of either the TC or BG. The Flow model solves the Reynolds equation of hydrodynamic lubrication coupled to a thermal energy transport equation to determine the film pressure and bulk temperature fields, respectively. The model predicts performance parameters such as power loss and Lubricant Flow Rate, and force and moment stiffness and damping coefficients. Predictions show that misaligning of either the thrust collar or bull gear alters the load-carrying area in the lubricated zone, shifts the pressure field with peak magnitudes doubling or more depending on the degree and direction of TC or BG misalignment. Static angular misalignment does not significantly affect the power loss, temperature rise, etc., but does have an effect on the dynamic coefficients (both axial and angular). Finally, a reduced complex dynamic stiffness matrix for the lubricated TC shows that some cross-coupled stiffness and moment coefficients are nonzero, indicating hydrodynamic coupling between axial and angular motions for the pinion and bull gear shafts. The coupling could affect the placement of the system natural frequencies and associated mode shapes as well as the system stability.
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On the Predicted Effect of Angular Misalignment on the Performance of Oil Lubricated Thrust Collars in Integrally Geared Compressors
Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 2016Co-Authors: Travis A. Cable, Luis San Andrés, Karl WygantAbstract:Multiple-stage integrally geared compressors (IGCs) offer improved thermal efficiency and easier access for maintenance and overhaul than single-shaft centrifugal compressors. In an IGC, a main bull shaft drives pinion shafts, each having an impeller at its ends. The compression of process gas in the compressor stages induces axial loads along the pinion shafts that are transmitted via thrust collars (TCs) to the main bull gear (BG) shaft and balanced by a single thrust bearing. Manufacturing inaccuracies and a poor assembly process can lead to static angular misalignments of the TC and BG surfaces that affect the operating film thickness as well as the force and reaction moments of the lubricated mechanical element. In a follow up to Ref. [1], this paper presents an investigation of the performance of a single thrust collar configuration operating with increasing static angular misalignment of either the TC or BG. The Flow model solves the Reynolds equation of hydrodynamic lubrication coupled to a thermal energy transport equation to determine the film pressure and bulk temperature fields, respectively. The model predicts performance parameters such as power loss and Lubricant Flow Rate, and force and moment stiffness and damping coefficients. Predictions show that misaligning of either the thrust collar or bull gear alters the load carrying area in the lubricated zone, shifts the pressure field with peak magnitudes doubling or more depending on the degree and direction of TC or BG misalignment. Static angular misalignment does not significantly affect the power loss, temperature rise, etc., but does have an effect on the dynamic coefficients (both axial and angular). Finally, a reduced complex dynamic stiffness matrix for the lubricated TC shows that some cross coupled stiffness and moment coefficients are nonzero, indicating hydrodynamic coupling between axial and angular motions for the pinion and bull gear shafts. The coupling could affect the placement of the system natural frequencies and associated mode shapes as well as the system stability.
Shuai Gao - One of the best experts on this subject based on the ideXlab platform.
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Ball bearing skidding and over-skidding in large-scale angular contact ball bearings: Nonlinear dynamic model with thermal effects and experimental results
Mechanical Systems and Signal Processing, 2021Co-Authors: Shuai Gao, Steven Chatterton, Lorenzo Naldi, Paolo PennacchiAbstract:Abstract 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.
