The Experts below are selected from a list of 261 Experts worldwide ranked by ideXlab platform
L.-x. Liu - One of the best experts on this subject based on the ideXlab platform.
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scaling laws for ultra short hydrostatic gas Journal Bearings
Journal of Vibration and Acoustics, 2005Co-Authors: Zoltán S. Spakovszky, L.-x. LiuAbstract:The Journal Bearings of the MIT micro-devices are located at the outer periphery of the rotor and are designed to operate at rotational speeds of order two million rpm in order to enable high-power densities with turbomachinery tip speeds near 500 m/s. These Journal Bearings are very short compared to their relatively large bearing diameters such that the bearing L/D is typically less than 0.1, that is at least one order of magnitude smaller than in conventional gas Bearings. Thus, the ultra-short micro gas Journal Bearings essentially act as short annular seals and operate at Reynolds numbers of order 300, two orders of magnitude lower than conventional annular seals. The concepts that hold for turbulent flow, large scale annular seals do not apply to micro Bearings and the laminar flow regime sets new challenges in the design, implementation and operation of ultra-short, high-speed gas Bearings. In order to reach the goal of operating the MIT micro devices at full design speed, the micro-bearing design must be improved and engineering solutions need to be found to overcome the challenges of high-speed bearing operation. This paper is the first to derive the scaling laws for the dynamics of ultra-short hydrostatic gas Journal Bearings. The theory is established from first principles and enables a physics based characterization of the dynamic behavior of ultra-short hydrostatic gas Bearings. The derived scaling laws for natural frequency and damping ratio show good agreement with experimental data. A simple criterion for whirl instability is found that only depends on bearing geometry. The scaling laws together with this criterion are used to delineate engineering solutions critical for stable high-speed bearing operation. Design charts are developed which provide the link between fabrication tolerances, bearing performance, and the tolerable level of rotor unbalance for a minimum required whirl ratio.
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Hydrostatic Gas Journal Bearings for Micro-Turbomachinery
Journal of Vibration and Acoustics, 2005Co-Authors: L.-x. Liu, Alan H. Epstein, C J Teo, Zoltán S. SpakovszkyAbstract:Several years ago an effort was undertaken at MIT to develop high-speed rotating MEMS (Micro Electro-Mechanical Systems) using computer chip fabrication technology,. To enable high-power density the micro-turbomachinery must be run at tip speeds of order 500 m/s, comparable to conventional scale turbomachinery. The high rotating speeds (of order 2 million rpm), the relatively low bearing aspect ratios (L/D < 0.1) due to fabrication constraints, and the laminar flow regime in the bearing gap place the microbearing designs to an exotic spot in the design space for hydrostatic, gas Bearings. This paper presents a new analytical model for axially fed gas Journal Bearings and reports the experimental testing of micro gas Bearings to characterize and to investigate their rotordynamic behavior The analytical model is capable of dealing with all the elements of (1) micro-devices, (2) dynamic response characteristics of hydrostatic gas Bearings, (3) evaluation of stiffness, natural frequency and damping, (4) evaluation of instability boundaries, and (5) evaluation of effects of imbalance and bearing anisotropy,. First, a newly developed analytical model for hydrostatic gas Journal Bearings is introduced. The model consists of two parts, a fluid dynamic model for axially, fed gas Journal Bearings and a rotordynamic model for micro-devices. Next, the model is used to predict the natural frequency, damping ratio and the instability boundanry for the test devices. Experiments are conducted using a high-resolution fiber optic sensor to measure rotor speed, and a data reduction scheme is implemented to obtain imbalance-driven whirl response curves. The model predictions are validated against experimental data and show good agreement with the measured natural frequencies and damping ratios. Last, the new model is successfully used to establish bearing operating protocols and guidelines for high-speed operation.
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hydrostatic gas Journal Bearings for micro turbomachinery
ASME 2003 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, 2003Co-Authors: L.-x. Liu, C J Teo, A H Epstei, Zoltán S. SpakovszkyAbstract:Several years ago an effort was undertaken at MIT to develop high-speed rotating MEMS (Micro Electro-Mechanical Systems) using computer chip fabrication technology. To enable high-power density the micro-turbomachinery must be run at tip speeds of order 500 m/s, comparable to conventional scale turbomachinery. The high rotating speeds (of order 2 million rpm), the relatively low bearing aspect ratios (L/D < 0.1) due to fabrication constraints, and the laminar flow regime in the bearing gap place the micro-bearing designs to an exotic spot in the design space for hydrostatic gas Bearings. This paper presents a new analytical model for axially fed gas Journal Bearings and reports the experimental testing of micro gas Bearings to characterize and to investigate their rotordynamic behavior. The analytical model is capable of dealing with all the elements of, (1) micro-devices, (2) dynamic response characteristics of hydrostatic gas Bearings, (3) evaluation of stiffness, natural frequency and damping, (4) evaluation of instability boundaries, and (5) evaluation of effects of imbalance and bearing anisotropy. First, a newly developed analytical model for hydrostatic gas Journal Bearings is introduced. The model consists of two parts, a fluid dynamic model for axially fed gas Journal Bearings and a rotordynamic model for micro-devices. Next, the model is used to predict the natural frequency, damping ratio and the instability boundary for the test devices. Experiments are conducted using a high-resolution fiber optic sensor to measure rotor speed, and a data reduction scheme is implemented to obtain imbalance-driven whirl response curves. The model predictions are validated against experimental data and show good agreement with the measured natural frequencies and damping ratios. Last, the new model is successfully used to establish bearing operating protocols and guidelines for high-speed operation.Copyright © 2003 by ASME
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scaling laws for ultra short hydrostatic gas Journal Bearings
ASME 2003 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, 2003Co-Authors: Zoltán S. Spakovszky, L.-x. LiuAbstract:The Journal Bearings of the MIT micro-devices are located at the outer periphery of the rotor and are designed to operate at rotational speeds of order 2 million rpm in order to enable high-power densities with turbomachinery tip speeds near 500 m/s. These Journal Bearings are very short compared to their relatively large bearing diameters such that the bearing L/D is typically less than 0.1, that is at least one order of magnitude smaller than in conventional gas Bearings. Thus, the ultra-short micro gas Journal Bearings essentially act as short annular seals and operate at Reynolds numbers of order 300, two orders of magnitude lower than conventional annular seals. The concepts that hold for turbulent flow, large scale annular seals do not apply to micro Bearings and the laminar flow regime sets new challenges in the design, implementation and operation of ultra-short, high-speed gas Bearings. In order to reach the goal of operating the MIT micro devices at full design speed, the micro-bearing design must be improved and engineering solutions need to be found to overcome the challenges of high-speed bearing operation. This paper is the first to derive the scaling laws for the dynamics of ultrashort hydrostatic gas Journal Bearings. The theory is established from first principles and enables a physics based characterization of the dynamic behavior of ultra-short hydrostatic gas Bearings. The derived scaling laws for natural frequency and damping ratio show good agreement with experimental data. A simple criterion for whirl instability is found that only depends on bearing geometry. The scaling laws together with this criterion are used to delineate engineering solutions critical for stable high-speed bearing operation. Design charts are developed which provide the link between fabrication tolerances, bearing performance, and the tolerable level of rotor unbalance for a minimum required whirl ratio.Copyright © 2003 by ASME
Zoltán S. Spakovszky - One of the best experts on this subject based on the ideXlab platform.
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scaling laws for ultra short hydrostatic gas Journal Bearings
Journal of Vibration and Acoustics, 2005Co-Authors: Zoltán S. Spakovszky, L.-x. LiuAbstract:The Journal Bearings of the MIT micro-devices are located at the outer periphery of the rotor and are designed to operate at rotational speeds of order two million rpm in order to enable high-power densities with turbomachinery tip speeds near 500 m/s. These Journal Bearings are very short compared to their relatively large bearing diameters such that the bearing L/D is typically less than 0.1, that is at least one order of magnitude smaller than in conventional gas Bearings. Thus, the ultra-short micro gas Journal Bearings essentially act as short annular seals and operate at Reynolds numbers of order 300, two orders of magnitude lower than conventional annular seals. The concepts that hold for turbulent flow, large scale annular seals do not apply to micro Bearings and the laminar flow regime sets new challenges in the design, implementation and operation of ultra-short, high-speed gas Bearings. In order to reach the goal of operating the MIT micro devices at full design speed, the micro-bearing design must be improved and engineering solutions need to be found to overcome the challenges of high-speed bearing operation. This paper is the first to derive the scaling laws for the dynamics of ultra-short hydrostatic gas Journal Bearings. The theory is established from first principles and enables a physics based characterization of the dynamic behavior of ultra-short hydrostatic gas Bearings. The derived scaling laws for natural frequency and damping ratio show good agreement with experimental data. A simple criterion for whirl instability is found that only depends on bearing geometry. The scaling laws together with this criterion are used to delineate engineering solutions critical for stable high-speed bearing operation. Design charts are developed which provide the link between fabrication tolerances, bearing performance, and the tolerable level of rotor unbalance for a minimum required whirl ratio.
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Hydrostatic Gas Journal Bearings for Micro-Turbomachinery
Journal of Vibration and Acoustics, 2005Co-Authors: L.-x. Liu, Alan H. Epstein, C J Teo, Zoltán S. SpakovszkyAbstract:Several years ago an effort was undertaken at MIT to develop high-speed rotating MEMS (Micro Electro-Mechanical Systems) using computer chip fabrication technology,. To enable high-power density the micro-turbomachinery must be run at tip speeds of order 500 m/s, comparable to conventional scale turbomachinery. The high rotating speeds (of order 2 million rpm), the relatively low bearing aspect ratios (L/D < 0.1) due to fabrication constraints, and the laminar flow regime in the bearing gap place the microbearing designs to an exotic spot in the design space for hydrostatic, gas Bearings. This paper presents a new analytical model for axially fed gas Journal Bearings and reports the experimental testing of micro gas Bearings to characterize and to investigate their rotordynamic behavior The analytical model is capable of dealing with all the elements of (1) micro-devices, (2) dynamic response characteristics of hydrostatic gas Bearings, (3) evaluation of stiffness, natural frequency and damping, (4) evaluation of instability boundaries, and (5) evaluation of effects of imbalance and bearing anisotropy,. First, a newly developed analytical model for hydrostatic gas Journal Bearings is introduced. The model consists of two parts, a fluid dynamic model for axially, fed gas Journal Bearings and a rotordynamic model for micro-devices. Next, the model is used to predict the natural frequency, damping ratio and the instability boundanry for the test devices. Experiments are conducted using a high-resolution fiber optic sensor to measure rotor speed, and a data reduction scheme is implemented to obtain imbalance-driven whirl response curves. The model predictions are validated against experimental data and show good agreement with the measured natural frequencies and damping ratios. Last, the new model is successfully used to establish bearing operating protocols and guidelines for high-speed operation.
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hydrostatic gas Journal Bearings for micro turbomachinery
ASME 2003 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, 2003Co-Authors: L.-x. Liu, C J Teo, A H Epstei, Zoltán S. SpakovszkyAbstract:Several years ago an effort was undertaken at MIT to develop high-speed rotating MEMS (Micro Electro-Mechanical Systems) using computer chip fabrication technology. To enable high-power density the micro-turbomachinery must be run at tip speeds of order 500 m/s, comparable to conventional scale turbomachinery. The high rotating speeds (of order 2 million rpm), the relatively low bearing aspect ratios (L/D < 0.1) due to fabrication constraints, and the laminar flow regime in the bearing gap place the micro-bearing designs to an exotic spot in the design space for hydrostatic gas Bearings. This paper presents a new analytical model for axially fed gas Journal Bearings and reports the experimental testing of micro gas Bearings to characterize and to investigate their rotordynamic behavior. The analytical model is capable of dealing with all the elements of, (1) micro-devices, (2) dynamic response characteristics of hydrostatic gas Bearings, (3) evaluation of stiffness, natural frequency and damping, (4) evaluation of instability boundaries, and (5) evaluation of effects of imbalance and bearing anisotropy. First, a newly developed analytical model for hydrostatic gas Journal Bearings is introduced. The model consists of two parts, a fluid dynamic model for axially fed gas Journal Bearings and a rotordynamic model for micro-devices. Next, the model is used to predict the natural frequency, damping ratio and the instability boundary for the test devices. Experiments are conducted using a high-resolution fiber optic sensor to measure rotor speed, and a data reduction scheme is implemented to obtain imbalance-driven whirl response curves. The model predictions are validated against experimental data and show good agreement with the measured natural frequencies and damping ratios. Last, the new model is successfully used to establish bearing operating protocols and guidelines for high-speed operation.Copyright © 2003 by ASME
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scaling laws for ultra short hydrostatic gas Journal Bearings
ASME 2003 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, 2003Co-Authors: Zoltán S. Spakovszky, L.-x. LiuAbstract:The Journal Bearings of the MIT micro-devices are located at the outer periphery of the rotor and are designed to operate at rotational speeds of order 2 million rpm in order to enable high-power densities with turbomachinery tip speeds near 500 m/s. These Journal Bearings are very short compared to their relatively large bearing diameters such that the bearing L/D is typically less than 0.1, that is at least one order of magnitude smaller than in conventional gas Bearings. Thus, the ultra-short micro gas Journal Bearings essentially act as short annular seals and operate at Reynolds numbers of order 300, two orders of magnitude lower than conventional annular seals. The concepts that hold for turbulent flow, large scale annular seals do not apply to micro Bearings and the laminar flow regime sets new challenges in the design, implementation and operation of ultra-short, high-speed gas Bearings. In order to reach the goal of operating the MIT micro devices at full design speed, the micro-bearing design must be improved and engineering solutions need to be found to overcome the challenges of high-speed bearing operation. This paper is the first to derive the scaling laws for the dynamics of ultrashort hydrostatic gas Journal Bearings. The theory is established from first principles and enables a physics based characterization of the dynamic behavior of ultra-short hydrostatic gas Bearings. The derived scaling laws for natural frequency and damping ratio show good agreement with experimental data. A simple criterion for whirl instability is found that only depends on bearing geometry. The scaling laws together with this criterion are used to delineate engineering solutions critical for stable high-speed bearing operation. Design charts are developed which provide the link between fabrication tolerances, bearing performance, and the tolerable level of rotor unbalance for a minimum required whirl ratio.Copyright © 2003 by ASME
Martin J Conlon - One of the best experts on this subject based on the ideXlab platform.
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operational performance of textured Journal Bearings lubricated with a contaminated fluid
Tribology International, 2016Co-Authors: Azzedine Dadouche, Martin J ConlonAbstract:Abstract Contemporary machinery are required to operate under more demanding conditions such as high-temperature or possible contaminated environments. Such situations affect the proper operation of rotating components and sealing systems and could reduce their service life. For instance, hydrodynamic Journal Bearings may suffer serious performance issues due to contamination from moisture, dust, foreign particles and wear debris. This experimental study investigates the effect of surface texturing on the steady-state performance characteristics of highly-loaded Journal Bearings lubricated with a contaminated lubricant. Special attention is given to the Bearings’ load capacity and friction and wear at various contamination levels in the lubricant. Rig tests have been performed at selected speeds and loads on plain smooth and surface-textured Journal Bearings. Variable-size test dust was introduced into the lubrication system (at different rates) upstream of the test bearing while bearing characteristics were measured. Conclusions are then drawn on the effectiveness of the dimples in capturing contaminant particles and reducing the possibility of bearing failure.
Satoru Kaneko - One of the best experts on this subject based on the ideXlab platform.
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Numerical and Experimental Analyses of the Dynamic Characteristics of Journal Bearings With Square Dimples
Journal of Tribology-transactions of The Asme, 2017Co-Authors: Hiroyuki Yamada, Hiroo Taura, Satoru KanekoAbstract:Numerous previous numerical studies have investigated the effect of surface texturing upon the static characteristics of Journal Bearings, including their load-carrying capacity and friction torque. In general, the dynamic characteristics of Journal Bearings are also important, since they are essential factors in predicting the vibration behavior of actual rotors supported by Journal Bearings. However, the effects of surface texture upon these dynamic characteristics have not been investigated through either numerical or experimental analysis. Thus, in the present study, such analyses were conducted to investigate the dynamic characteristics of textured Journal Bearings, such as their dynamic coefficients of oil film and the stability-threshold shaft speed supported by the Bearings. Numerical analysis was done using a model that included inertial effects and energy loss; this model agreed well with experimental results concerning static characteristics from our previous study. Dynamic testing based on a sinusoidal-excitation method was also performed using textured Journal Bearings with uniform square dimples to verify the numerical results, which agreed qualitatively with those of experiment, confirming the validity of the numerical analysis. These results suggest that under the same operating conditions, the main effect of texturing upon the dynamic coefficients is to yield the cross-coupled stiffness coefficients with lower absolute values than the conventional ones with a smooth surface. The linear stability-threshold shaft speed of the rotor supported by the textured Journal Bearings became higher than that of a smooth bearing, mainly due to the reduction of cross-coupled stiffness coefficients. This tendency became more pronounced for high Reynolds number operating conditions and textured Bearings with a large number of dimples.
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Static Characteristics of Journal Bearings With Square Dimples
Journal of Tribology-transactions of The Asme, 2017Co-Authors: Hiroyuki Yamada, Hiroo Taura, Satoru KanekoAbstract:Surface texturing is a technique for improving frictional and hydrodynamic performances of Journal Bearings because microtextures can serve as reservoirs for oil or traps for debris and may also generate hydrodynamic pressure. Over the past two decades, many researchers have experimentally demonstrated that texturing of various tribological elements can reduce friction force and wear, contributing to improvement of lubrication performance. Some numerical studies have examined the hydrodynamic lubrication conditions and reported that surface texturing affects the static characteristics of Journal Bearings, such as their load carrying capacity and friction torque. However, the validity of these numerical models has not been confirmed because of a lack of experimental studies. This study proposes a numerical model that includes both inertial effects and energy loss at the edges of dimples on the surface of a Journal bearing in order to investigate the bearing's static characteristics. Experimental verification of Journal Bearings is also conducted with a uniform square-dimple pattern on their full-bearing surface. The results obtained by the model agree well with those of experiment, confirming the model's validity. These results show that under the same operating conditions, textured Bearings yield a higher eccentricity ratio and lower attitude angle than the conventional ones with a smooth surface. This tendency becomes more marked for high Reynolds number operating conditions and for textured Bearings with a large number of dimples.
Yong-joo Cho - One of the best experts on this subject based on the ideXlab platform.
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Comparison of power loss and pad temperature for leading edge groove tilting pad Journal Bearings and conventional tilting pad Journal Bearings
Tribology International, 2010Co-Authors: Kyung-bo Bang, Jeong-hun Kim, Yong-joo ChoAbstract:Abstract A study was undertaken to compare power loss and pad temperature characteristics between LEG (leading edge groove) tilting pad Journal Bearings and conventional tilting pad Journal Bearings with and without a seal tooth. All test Bearings were double tilting type with six-pad LOP (Load On Pad), 300.6 mm inner diameter, and 120.0 mm effective length. Pad temperatures and power losses were compared and evaluated versus rotor rotational speed, oil flow rate, and static load. Four kinds of tilting pad Journal Bearings were evaluated, conventional tilting pad Journal Bearings with and without a seal tooth and LEG tilting pad Journal Bearings with and without a seal tooth. Test results indicate that tilting pad Journal Bearings without a seal tooth have lower power loss and pad temperature than tilting pad Journal Bearings with a seal tooth. Especially, conventional tilting pad Journal bearing without a seal tooth has the lowest power loss and pad temperature among the test Bearings.
