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Effects of mesh density on static load performance of metal mesh gas foil bearings / Yong-Bok Lee in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 134 N° 1 (Janvier 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 134 N° 1 (Janvier 2012) . - 08 p. Titre : Effects of mesh density on static load performance of metal mesh gas foil bearings Type de document : texte imprimé Auteurs : Yong-Bok Lee, Auteur ; Chang Ho Kim, Auteur ; Tae Ho Kim, Auteur ; Young Tae Kim, Auteur Année de publication : 2012 Article en page(s) : 08 p. Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Damping  Elastic  constants  Machine  bearings  Net  structures  (mechanical)  Rotors  Stainless  steel Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Metal mesh materials have been used successfully in vibration isolators and bearing dampers due to their superior friction or hysteresis damping mechanism. These materials are formed to metal mesh (or wire mesh) structures in ring-shape by compressing a weave of metal wires, in general. Recently, oil-free rotating machinery implement metal mesh structures into hydrodynamic gas foil bearings by replacing bump strip layers with them, to increase its bearing structural damping. A metal mesh foil bearing (MMFB) consists of a top foil and support elastic metal mesh pads installed between a rotating shaft and a housing. The present research presents load capacity tests of a MMFB at rotor rest (0 rpm) and 30 krpm for three metal mesh densities of 13.1%, 23.2%, and 31.6%. The metal mesh pad of test MMFB is made using a stainless steel wire with a diameter of 0.15 mm. Test rig comprises a rigid rotor with a diameter of 60 mm supported on two ball bearings at both ends and test MMFB with an axial length of 50 mm floats on the rotor. Static loads is provided with a mechanical loading device on test MMFB and a strain gauge type load cell measures the applied static loads. A series of static load versus deflection tests were conducted for selected metal mesh densities at rest (0 rpm). Test data are compared to further test results of static load versus journal eccentricity recorded at the rotor speed of 30 krpm. Test data show a strong nonlinearity of bearing deflection (journal eccentricity) with static load, independent of rotor spinning. Observed hysteresis loops imply significant structural damping of test MMFB. Measured journal deflections at 0 rpm are in similar trend to recorded journal eccentricities at the finite rotor speed; thus implying that the MMFB performance depends mainly on the metal mesh structures. The paper also estimates linearlized stiffness coefficient and damping loss factor of test MMFB using the measured static load versus deflection test data at 0 rpm and 30 krpm. The results show that the highest mesh density of 31.6% produces highest linearlized stiffness coefficient and damping loss factor. With rotor spinning at 30 krpm, the linearlized stiffness coefficient and damping loss factor decrease slightly, independent of metal mesh densities. The present test data will serve as a database for benchmarking MMFB predictive models. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000001 [...] [article] Effects of mesh density on static load performance of metal mesh gas foil bearings [texte imprimé] / Yong-Bok Lee, Auteur ; Chang Ho Kim, Auteur ; Tae Ho Kim, Auteur ; Young Tae Kim, Auteur . - 2012 . - 08 p. Génie mécanique Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 134 N° 1 (Janvier 2012) . - 08 p. Mots-clés : Damping  Elastic  constants  Machine  bearings  Net  structures  (mechanical)  Rotors  Stainless  steel Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Metal mesh materials have been used successfully in vibration isolators and bearing dampers due to their superior friction or hysteresis damping mechanism. These materials are formed to metal mesh (or wire mesh) structures in ring-shape by compressing a weave of metal wires, in general. Recently, oil-free rotating machinery implement metal mesh structures into hydrodynamic gas foil bearings by replacing bump strip layers with them, to increase its bearing structural damping. A metal mesh foil bearing (MMFB) consists of a top foil and support elastic metal mesh pads installed between a rotating shaft and a housing. The present research presents load capacity tests of a MMFB at rotor rest (0 rpm) and 30 krpm for three metal mesh densities of 13.1%, 23.2%, and 31.6%. The metal mesh pad of test MMFB is made using a stainless steel wire with a diameter of 0.15 mm. Test rig comprises a rigid rotor with a diameter of 60 mm supported on two ball bearings at both ends and test MMFB with an axial length of 50 mm floats on the rotor. Static loads is provided with a mechanical loading device on test MMFB and a strain gauge type load cell measures the applied static loads. A series of static load versus deflection tests were conducted for selected metal mesh densities at rest (0 rpm). Test data are compared to further test results of static load versus journal eccentricity recorded at the rotor speed of 30 krpm. Test data show a strong nonlinearity of bearing deflection (journal eccentricity) with static load, independent of rotor spinning. Observed hysteresis loops imply significant structural damping of test MMFB. Measured journal deflections at 0 rpm are in similar trend to recorded journal eccentricities at the finite rotor speed; thus implying that the MMFB performance depends mainly on the metal mesh structures. The paper also estimates linearlized stiffness coefficient and damping loss factor of test MMFB using the measured static load versus deflection test data at 0 rpm and 30 krpm. The results show that the highest mesh density of 31.6% produces highest linearlized stiffness coefficient and damping loss factor. With rotor spinning at 30 krpm, the linearlized stiffness coefficient and damping loss factor decrease slightly, independent of metal mesh densities. The present test data will serve as a database for benchmarking MMFB predictive models. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000001 [...]

A New Switching Strategy for Pulse Width Modulation (PWM) Power Converters / Kyu Min Cho in IEEE transactions on industrial electronics, Vol. 54 N°1 (Fevrier 2007) 

Public ISBD [article]  in IEEE transactions on industrial electronics > Vol. 54 N°1 (Fevrier 2007) . - 330-337 p. Titre : A New Switching Strategy for Pulse Width Modulation (PWM) Power Converters Titre original : Une Nouvelle Stratégie de Commutation pour des Convertisseurs de Puissance de la Modulation de Largeur d'Impulsion (PWM) Type de document : texte imprimé Auteurs : Kyu Min Cho, Auteur ; Won Seok Oh, Auteur ; Young Tae Kim ; Hee Jun Kim, Auteur Article en page(s) : 330-337 p. Note générale : Génie Electrique Langues : Anglais (eng) Mots-clés : Dead  time  effect  Power  converters  Pulse  width  modulation  Switching  strategy.Effet  de  temps  mort  Convertisseurs  de  puissance  Modulation  de  largeur  d'impulsion  Stratégie  de  commutation. Index. décimale : 621.38 Dispositifs électroniques. Tubes à électrons. Photocellules. Accélérateurs de particules. Tubes à rayons X Résumé : This paper presents a new switching strategy for pulse width modulation (PWM) power converters. Since the proposed strategy uses independent on/off switching action of the upper or lower arm according to the polarity of the current, the dead time is not needed except instant of current polarity change. Therefore, it is not necessary to compensate the dead time effect and the possibility of arm short is strongly eliminated. The current control of PWM power converters can easily adopt the proposed switching strategy by using the polarity information of the reference current instead of the real current, thus eliminating the problems that commonly arise from real current detection. In order to confirm the usefulness of the proposed switching strategy, experimental tests were done using a single-phase inverter with passive loads, a three-phase inverter for induction motor drives, a three-phase ac/dc PWM converter, a three-phase active power filter, and a class-D amplifier, the results of which are presented in this paper. Cet article présente une nouvelle stratégie de commutation pour des convertisseurs de puissance de la modulation de largeur d'impulsion (PWM). Puisque la stratégie proposée emploie l'action "Marche/Arrêt" indépendante de commutation du bras supérieur ou inférieur selon la polarité du courant, le temps mort n'est pas nécessaire à moins qu'instant de changement courant de polarité. Par conséquent, il n'est pas nécessaire de compenser l'effet de temps mort et la possibilité de short de bras est fortement éliminée. La commande courante des convertisseurs de puissance de PWM peut facilement adopter la stratégie de changement proposée en employant l'information de polarité du courant de référence au lieu du vrai courant, de ce fait éliminant les problèmes qui résultent généralement de la vraie détection courante. Afin de confirmer l'utilité de la stratégie de changement proposée, des essais expérimentaux ont été faits à l'aide d'un inverseur monophasé avec les charges passives, d'un inverseur triphasé pour des commandes de moteur à induction, d'un convertisseur triphasé d'ac/dc PWM, d'un filtre actif triphasé de puissance, et d'un amplificateur de classe-d, les résultats dont sont présentés en cet article. DEWEY : 621 ISSN : 02780046 RAMEAU : Convertisseur En ligne : hjkim@hanyang.ac.kr [article] A New Switching Strategy for Pulse Width Modulation (PWM) Power Converters = Une Nouvelle Stratégie de Commutation pour des Convertisseurs de Puissance de la Modulation de Largeur d'Impulsion (PWM) [texte imprimé] / Kyu Min Cho, Auteur ; Won Seok Oh, Auteur ; Young Tae Kim ; Hee Jun Kim, Auteur . - 330-337 p. Génie Electrique Langues : Anglais (eng) in IEEE transactions on industrial electronics > Vol. 54 N°1 (Fevrier 2007) . - 330-337 p. Mots-clés : Dead  time  effect  Power  converters  Pulse  width  modulation  Switching  strategy.Effet  de  temps  mort  Convertisseurs  de  puissance  Modulation  de  largeur  d'impulsion  Stratégie  de  commutation. Index. décimale : 621.38 Dispositifs électroniques. Tubes à électrons. Photocellules. Accélérateurs de particules. Tubes à rayons X Résumé : This paper presents a new switching strategy for pulse width modulation (PWM) power converters. Since the proposed strategy uses independent on/off switching action of the upper or lower arm according to the polarity of the current, the dead time is not needed except instant of current polarity change. Therefore, it is not necessary to compensate the dead time effect and the possibility of arm short is strongly eliminated. The current control of PWM power converters can easily adopt the proposed switching strategy by using the polarity information of the reference current instead of the real current, thus eliminating the problems that commonly arise from real current detection. In order to confirm the usefulness of the proposed switching strategy, experimental tests were done using a single-phase inverter with passive loads, a three-phase inverter for induction motor drives, a three-phase ac/dc PWM converter, a three-phase active power filter, and a class-D amplifier, the results of which are presented in this paper. Cet article présente une nouvelle stratégie de commutation pour des convertisseurs de puissance de la modulation de largeur d'impulsion (PWM). Puisque la stratégie proposée emploie l'action "Marche/Arrêt" indépendante de commutation du bras supérieur ou inférieur selon la polarité du courant, le temps mort n'est pas nécessaire à moins qu'instant de changement courant de polarité. Par conséquent, il n'est pas nécessaire de compenser l'effet de temps mort et la possibilité de short de bras est fortement éliminée. La commande courante des convertisseurs de puissance de PWM peut facilement adopter la stratégie de changement proposée en employant l'information de polarité du courant de référence au lieu du vrai courant, de ce fait éliminant les problèmes qui résultent généralement de la vraie détection courante. Afin de confirmer l'utilité de la stratégie de changement proposée, des essais expérimentaux ont été faits à l'aide d'un inverseur monophasé avec les charges passives, d'un inverseur triphasé pour des commandes de moteur à induction, d'un convertisseur triphasé d'ac/dc PWM, d'un filtre actif triphasé de puissance, et d'un amplificateur de classe-d, les résultats dont sont présentés en cet article. DEWEY : 621 ISSN : 02780046 RAMEAU : Convertisseur En ligne : hjkim@hanyang.ac.kr

Rotordynamic performance of an oil-free turbo blower focusing on load capacity of gas foil thrust bearings / Tae Ho Kim in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 134 N° 2 (Février 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 134 N° 2 (Février 2012) . - 07 p. Titre : Rotordynamic performance of an oil-free turbo blower focusing on load capacity of gas foil thrust bearings Type de document : texte imprimé Auteurs : Tae Ho Kim, Auteur ; Yong-Bok Lee, Auteur ; Young Tae Kim, Auteur ; Kyong Ho Jeong, Auteur Année de publication : 2012 Article en page(s) : 07 p. Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Compressed  air  systems  Finite  element  analysis  Hydrodynamics  Impellers  Rolling  bearings  Rotors  Turbomachinery Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Engineered design of modern efficient turbomachinery based on accurate model predictions is of importance as operating speed and rate power increase. Industrial applications use hydrodynamic fluid film bearings as rotor support elements due to their advantages over rolling element bearings in operating speed, system stability (rotordynamic and thermal), and maintenance life. Recently, microturbomachinery (< 250 kW) implement gas foil bearings (GFBs) as its rotor supports due to its compact design without lubricant supply systems and enhanced stability characteristics. To meet the needs from manufacturers, the turbomachinery development procedure includes a rotordynamic design and a gas foil journal bearing (GFJB) analysis in general. The present research focuses on the role of gas foil thrust bearings (GFJBs) supporting axial load (static and dynamic) in an oil-free turbo blower with a 75 kW (100 HP) rate power at 30,000 rpm. The turbo blower provides a compressed air with a pressure ratio of 1.6 at a mass flow rate of 0.92 kg/s, using a centrifugal impeller installed at the rotor end. Two GFJBs with a diameter of 66mm and a length of 50 mm and one pair of GFTB with an outer diameter of 144 mm and an inner diameter of 74 mm support the rotor with an axial length of 493 mm and a weight of 12.7 kg. A finite element rotordynamic model prediction using predicted linearized GFJB force coefficients designs the rotor-GFB system with stability at the rotor speed of 30,000 rpm. Model predictions of the GFTB show axial load carrying performance. Experimental tests on the designed turbo blower; however, demonstrate unexpected large amplitudes of subsynchronous rotor lateral motions. Post-inspection reveals minor rubbing signs on the GFJB top foils and significant wear on the GFTB top foil. Therefore, GFTB is redesigned to have the larger outer diameter of 166 mm for the enhanced load capacity, i.e., 145%, increase in its loading area. The modification improves the rotor-GFB system performance with dominant synchronous motions up to the rate speed of 30,000 rpm. In addition, the paper studies the effect of GFTB tilting angles on the system performance. Insertion of shims between the GFTB brackets changes the bearing tilting angles. Model predictions show the decrease in the thrust load capacity by as large as 86% by increase in the tilting angle to 0.0006 rad (0.03438 deg). Experimental test data verify the computational model predictions. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000002 [...] [article] Rotordynamic performance of an oil-free turbo blower focusing on load capacity of gas foil thrust bearings [texte imprimé] / Tae Ho Kim, Auteur ; Yong-Bok Lee, Auteur ; Young Tae Kim, Auteur ; Kyong Ho Jeong, Auteur . - 2012 . - 07 p. Génie mécanique Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 134 N° 2 (Février 2012) . - 07 p. Mots-clés : Compressed  air  systems  Finite  element  analysis  Hydrodynamics  Impellers  Rolling  bearings  Rotors  Turbomachinery Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Engineered design of modern efficient turbomachinery based on accurate model predictions is of importance as operating speed and rate power increase. Industrial applications use hydrodynamic fluid film bearings as rotor support elements due to their advantages over rolling element bearings in operating speed, system stability (rotordynamic and thermal), and maintenance life. Recently, microturbomachinery (< 250 kW) implement gas foil bearings (GFBs) as its rotor supports due to its compact design without lubricant supply systems and enhanced stability characteristics. To meet the needs from manufacturers, the turbomachinery development procedure includes a rotordynamic design and a gas foil journal bearing (GFJB) analysis in general. The present research focuses on the role of gas foil thrust bearings (GFJBs) supporting axial load (static and dynamic) in an oil-free turbo blower with a 75 kW (100 HP) rate power at 30,000 rpm. The turbo blower provides a compressed air with a pressure ratio of 1.6 at a mass flow rate of 0.92 kg/s, using a centrifugal impeller installed at the rotor end. Two GFJBs with a diameter of 66mm and a length of 50 mm and one pair of GFTB with an outer diameter of 144 mm and an inner diameter of 74 mm support the rotor with an axial length of 493 mm and a weight of 12.7 kg. A finite element rotordynamic model prediction using predicted linearized GFJB force coefficients designs the rotor-GFB system with stability at the rotor speed of 30,000 rpm. Model predictions of the GFTB show axial load carrying performance. Experimental tests on the designed turbo blower; however, demonstrate unexpected large amplitudes of subsynchronous rotor lateral motions. Post-inspection reveals minor rubbing signs on the GFJB top foils and significant wear on the GFTB top foil. Therefore, GFTB is redesigned to have the larger outer diameter of 166 mm for the enhanced load capacity, i.e., 145%, increase in its loading area. The modification improves the rotor-GFB system performance with dominant synchronous motions up to the rate speed of 30,000 rpm. In addition, the paper studies the effect of GFTB tilting angles on the system performance. Insertion of shims between the GFTB brackets changes the bearing tilting angles. Model predictions show the decrease in the thrust load capacity by as large as 86% by increase in the tilting angle to 0.0006 rad (0.03438 deg). Experimental test data verify the computational model predictions. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000002 [...]