Documents disponibles écrits par cet auteur

Identification of rotordynamic force coefficients of a metal mesh foil bearing using impact load excitations / Luis San Andrés in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 133 N° 11 (Novembre 2011) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 133 N° 11 (Novembre 2011) . - 09 p. Titre : Identification of rotordynamic force coefficients of a metal mesh foil bearing using impact load excitations Type de document : texte imprimé Auteurs : Luis San Andrés, Auteur ; Thomas Abraham Chirathadam, Auteur Année de publication : 2012 Article en page(s) : 09 p. Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Damping  Elastic  constants  Impact  (mechanical)  Machine  bearings  Rotors  Stress  analysis  Turbomachinery Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Metal mesh foil bearings (MMFBs) are inexpensive compliant gas bearing type that aim to enable high speed, high temperature operation of small turbomachinery. A MMFB with an inner diameter of 28.00 mm and length of 28.05 mm is constructed with low cost and common materials. The bearing incorporates a copper mesh ring, 20% in compactness, and offering large material damping beneath a 0.127 mm thick preformed top foil. Prior experimentations (published papers) provide the bearing structure force coefficients and the break away torque for bearing lift off. Presently, the MMFB replaces a compressor in a small turbocharger driven test rig. Impact load tests aid to identify the direct and cross-coupled rotor dynamic force coefficients of the floating MMFB while operating at a speed of 50 krpm. Tests conducted with and without shaft rotation show the MMFB direct stiffness is less than its structural (static) stiffness, ~25% lower at an excitation frequency of 200 Hz. The thin air film acting in series with the metal mesh support and separating the rotating shaft and the bearing inner surface while airborne reduces the bearing stiffness. The equivalent viscous damping is nearly identical with and without shaft rotation. The identified loss factor, best representing the hysteretic type damping from the metal mesh, is high at ~0.50 in the frequency range 0–200 Hz. This magnitude reveals large mechanical energy dissipation ability from the MMFB. The measurements also show appreciable cross directional motions from the unidirectional impact loads, thus generating appreciable cross-coupled force coefficients. Rotor speed coast down measurements reveal pronounced subsynchronous whirl motion amplitudes locked at distinct frequencies. The MMFB stiffness hardening nonlinearity produces the rich frequency forced response. The synchronous as well as subsynchronous motions peak while the shaft traverses its critical speeds. The measurements establish reliable operation of the test MMFB while airborne. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013 [...] [article] Identification of rotordynamic force coefficients of a metal mesh foil bearing using impact load excitations [texte imprimé] / Luis San Andrés, Auteur ; Thomas Abraham Chirathadam, Auteur . - 2012 . - 09 p. Génie Mécanique Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 133 N° 11 (Novembre 2011) . - 09 p. Mots-clés : Damping  Elastic  constants  Impact  (mechanical)  Machine  bearings  Rotors  Stress  analysis  Turbomachinery Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Metal mesh foil bearings (MMFBs) are inexpensive compliant gas bearing type that aim to enable high speed, high temperature operation of small turbomachinery. A MMFB with an inner diameter of 28.00 mm and length of 28.05 mm is constructed with low cost and common materials. The bearing incorporates a copper mesh ring, 20% in compactness, and offering large material damping beneath a 0.127 mm thick preformed top foil. Prior experimentations (published papers) provide the bearing structure force coefficients and the break away torque for bearing lift off. Presently, the MMFB replaces a compressor in a small turbocharger driven test rig. Impact load tests aid to identify the direct and cross-coupled rotor dynamic force coefficients of the floating MMFB while operating at a speed of 50 krpm. Tests conducted with and without shaft rotation show the MMFB direct stiffness is less than its structural (static) stiffness, ~25% lower at an excitation frequency of 200 Hz. The thin air film acting in series with the metal mesh support and separating the rotating shaft and the bearing inner surface while airborne reduces the bearing stiffness. The equivalent viscous damping is nearly identical with and without shaft rotation. The identified loss factor, best representing the hysteretic type damping from the metal mesh, is high at ~0.50 in the frequency range 0–200 Hz. This magnitude reveals large mechanical energy dissipation ability from the MMFB. The measurements also show appreciable cross directional motions from the unidirectional impact loads, thus generating appreciable cross-coupled force coefficients. Rotor speed coast down measurements reveal pronounced subsynchronous whirl motion amplitudes locked at distinct frequencies. The MMFB stiffness hardening nonlinearity produces the rich frequency forced response. The synchronous as well as subsynchronous motions peak while the shaft traverses its critical speeds. The measurements establish reliable operation of the test MMFB while airborne. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013 [...]

Measurement of structural stiffness and damping coefficients in a metal mesh foil bearing / Luis San Andrés in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 132 N° 3 (Mars 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 132 N° 3 (Mars 2010) . - 07 p. Titre : Measurement of structural stiffness and damping coefficients in a metal mesh foil bearing Type de document : texte imprimé Auteurs : Luis San Andrés, Auteur ; Thomas Abraham Chirathadam, Auteur ; Tae Ho Kim, Auteur Année de publication : 2010 Article en page(s) : 07 p. Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Creep  Damping  Dynamic  testing  Elasticity  Foils  Machine  bearings  Micromechanical  devices  Rings  (structures)  Shafts  Turbomachinery Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Engineered metal mesh foil bearings (MMFBs) are a promising low cost bearing technology for oil-free microturbomachinery. In a MMFB, a ring shaped metal mesh provides a soft elastic support to a smooth arcuate foil wrapped around a rotating shaft. This paper details the construction of a MMFB and the static and dynamic load tests conducted on the bearing for estimation of its structural stiffness and equivalent viscous damping. The 28.00 mm diameter 28.05 mm long bearing, with a metal mesh ring made of 0.3 mm copper wire and compactness of 20%, is installed on a test shaft with a slight preload. Static load versus bearing deflection measurements display a cubic nonlinearity with large hysteresis. The bearing deflection varies linearly during loading, but nonlinearly during the unloading process. An electromagnetic shaker applies on the test bearing loads of controlled amplitude over a frequency range. In the frequency domain, the ratio of applied force to bearing deflection gives the bearing mechanical impedance, whose real part and imaginary part give the structural stiffness and damping coefficients, respectively. As with prior art published in the literature, the bearing stiffness decreases significantly with the amplitude of motion and shows a gradual increasing trend with frequency. The bearing equivalent viscous damping is inversely proportional to the excitation frequency and motion amplitude. Hence, it is best to describe the mechanical energy dissipation characteristics of the MMFB with a structural loss factor (material damping). The experimental results show a loss factor as high as 0.7 though dependent on the amplitude of motion. Empirically based formulas, originally developed for metal mesh rings, predict bearing structural stiffness and damping coefficients that agree well with the experimentally estimated parameters. Note, however, that the metal mesh ring, after continuous operation and various dismantling and re-assembly processes, showed significant creep or sag that resulted in a gradual decrease in its structural force coefficients. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000132000003 [...] [article] Measurement of structural stiffness and damping coefficients in a metal mesh foil bearing [texte imprimé] / Luis San Andrés, Auteur ; Thomas Abraham Chirathadam, Auteur ; Tae Ho Kim, Auteur . - 2010 . - 07 p. Génie Mécanique Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 132 N° 3 (Mars 2010) . - 07 p. Mots-clés : Creep  Damping  Dynamic  testing  Elasticity  Foils  Machine  bearings  Micromechanical  devices  Rings  (structures)  Shafts  Turbomachinery Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Engineered metal mesh foil bearings (MMFBs) are a promising low cost bearing technology for oil-free microturbomachinery. In a MMFB, a ring shaped metal mesh provides a soft elastic support to a smooth arcuate foil wrapped around a rotating shaft. This paper details the construction of a MMFB and the static and dynamic load tests conducted on the bearing for estimation of its structural stiffness and equivalent viscous damping. The 28.00 mm diameter 28.05 mm long bearing, with a metal mesh ring made of 0.3 mm copper wire and compactness of 20%, is installed on a test shaft with a slight preload. Static load versus bearing deflection measurements display a cubic nonlinearity with large hysteresis. The bearing deflection varies linearly during loading, but nonlinearly during the unloading process. An electromagnetic shaker applies on the test bearing loads of controlled amplitude over a frequency range. In the frequency domain, the ratio of applied force to bearing deflection gives the bearing mechanical impedance, whose real part and imaginary part give the structural stiffness and damping coefficients, respectively. As with prior art published in the literature, the bearing stiffness decreases significantly with the amplitude of motion and shows a gradual increasing trend with frequency. The bearing equivalent viscous damping is inversely proportional to the excitation frequency and motion amplitude. Hence, it is best to describe the mechanical energy dissipation characteristics of the MMFB with a structural loss factor (material damping). The experimental results show a loss factor as high as 0.7 though dependent on the amplitude of motion. Empirically based formulas, originally developed for metal mesh rings, predict bearing structural stiffness and damping coefficients that agree well with the experimentally estimated parameters. Note, however, that the metal mesh ring, after continuous operation and various dismantling and re-assembly processes, showed significant creep or sag that resulted in a gradual decrease in its structural force coefficients. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000132000003 [...]

Measurements of drag torque, lift-off journal speed, and temperature in a metal mesh foil bearing / Luis San Andrés in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 132 N° 11 (Novembre 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 132 N° 11 (Novembre 2010) . - 07 p. Titre : Measurements of drag torque, lift-off journal speed, and temperature in a metal mesh foil bearing Type de document : texte imprimé Auteurs : Luis San Andrés, Auteur ; Thomas Abraham Chirathadam, Auteur ; Ryu, Keun, Auteur Année de publication : 2011 Article en page(s) : 07 p. Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Automotive  engineering  Helicopters  Lubricating  oils  Machine  bearings  Rotary  engines  Torque  measurement  Turbines Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Metal mesh foil bearings (MMFBs) are a promising low cost gas bearing technology for high performance oil-free microturbomachinery. Elimination of complex oil lubrication and sealing system by deploying MMFBs in rotorcraft gas turbine engines offers distinctive advantages such as reduced system weight, enhanced reliability at high rotational speeds and extreme temperatures, and extended maintenance intervals compared with mineral oil lubricated bearings. MMFBs for oil-free rotorcraft engines must demonstrate adequate load capacity, reliable rotordynamic performance, and low frictional losses in a high temperature environment. The paper presents the measurements of MMFB break-away torque, rotor lift-off and touchdown speeds, and temperature at increasing static load conditions. The tests, which were conducted in a test rig driven by an automotive turbocharger turbine, demonstrate the airborne operation (hydrodynamic gas film) of the floating test MMFB with little frictional loses at increasing loads. The measured drag torque peaks when the rotor starts and stops, and drops significantly once the bearing lifts off. The estimated rotor speed for lift-off increases linearly with the applied static load. During continuous operation, the MMFB temperature measured at the back surface of the top foil increases both with rotor speed and static load. Nonetheless, the temperature rise is mild, demonstrating reliable performance. Application of a sacrificial layer of solid lubricant on the top foil surface reduces the rotor break-away torque. The measurements give confidence on this simple bearing technology for ready application into oil-free turbomachinery. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013 [...] [article] Measurements of drag torque, lift-off journal speed, and temperature in a metal mesh foil bearing [texte imprimé] / Luis San Andrés, Auteur ; Thomas Abraham Chirathadam, Auteur ; Ryu, Keun, Auteur . - 2011 . - 07 p. Génie Mécanique Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 132 N° 11 (Novembre 2010) . - 07 p. Mots-clés : Automotive  engineering  Helicopters  Lubricating  oils  Machine  bearings  Rotary  engines  Torque  measurement  Turbines Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Metal mesh foil bearings (MMFBs) are a promising low cost gas bearing technology for high performance oil-free microturbomachinery. Elimination of complex oil lubrication and sealing system by deploying MMFBs in rotorcraft gas turbine engines offers distinctive advantages such as reduced system weight, enhanced reliability at high rotational speeds and extreme temperatures, and extended maintenance intervals compared with mineral oil lubricated bearings. MMFBs for oil-free rotorcraft engines must demonstrate adequate load capacity, reliable rotordynamic performance, and low frictional losses in a high temperature environment. The paper presents the measurements of MMFB break-away torque, rotor lift-off and touchdown speeds, and temperature at increasing static load conditions. The tests, which were conducted in a test rig driven by an automotive turbocharger turbine, demonstrate the airborne operation (hydrodynamic gas film) of the floating test MMFB with little frictional loses at increasing loads. The measured drag torque peaks when the rotor starts and stops, and drops significantly once the bearing lifts off. The estimated rotor speed for lift-off increases linearly with the applied static load. During continuous operation, the MMFB temperature measured at the back surface of the top foil increases both with rotor speed and static load. Nonetheless, the temperature rise is mild, demonstrating reliable performance. Application of a sacrificial layer of solid lubricant on the top foil surface reduces the rotor break-away torque. The measurements give confidence on this simple bearing technology for ready application into oil-free turbomachinery. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ00013 [...]

A metal mesh foil bearing and a bump-type foil bearing / Luis San Andrés in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 134 N° 10 (Octobre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 134 N° 10 (Octobre 2012) . - 13 p. Titre : A metal mesh foil bearing and a bump-type foil bearing : comparison of performance for two similar size gas bearings Type de document : texte imprimé Auteurs : Luis San Andrés, Auteur ; Thomas Abraham Chirathadam, Auteur Année de publication : 2012 Article en page(s) : 13 p. Note générale : gas turbines Langues : Anglais (eng) Mots-clés : gas  bearings;  bump-type  foil  bearings  (BFBs);  overleaf-type  foil  bearings Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Gas bearings in oil-free microturbomachinery for gas process applications and power generation (<400 kW) must be reliable and inexpensive, ensuring low drag power and thermal stability. Bump-type foil bearings (BFBs) and overleaf-type foil bearings are in use in specialized applications, though their development time (design and prototyping), exotic materials, and excessive manufacturing cost still prevent their widespread usage. Metal mesh foil bearings (MMFBs), on the other hand, are an inexpensive alternative that use common materials and no restrictions on intellectual property. Laboratory testing shows that prototype MMFBs perform similarly as typical BFBs, but offer significantly larger damping to dissipate mechanical energy due to rotor vibrations. This paper details a one-to-one comparison of the static and dynamic forced performance characteristics of a MMFB against a BFB of similar size and showcases the advantages and disadvantages of MMFBs. The bearings for comparison are a generation I BFB and a MMFB, both with a slenderness ratio L/D = 1.04. Measurements of rotor lift-off speed and drag friction at start-up and airborne conditions were conducted for rotor speeds to 70 krpm and under identical specific loads (W/LD = 0.06 to 0.26 bar). Static load versus bearing elastic deflection tests evidence a typical hardening nonlinearity with mechanical hysteresis, the MMFB showing two to three times more material damping than the BFB. The MMFB exhibits larger drag torques during rotor start-up, and shut-down tests though bearing lift-off happens at lower rotor speeds (~15 krpm). As the rotor becomes airborne, both bearings offer very low drag friction coefficients, ~0.03 for the MMFB and ~0.04 for the BFB in the speed range 20–40 krpm. With the bearings floating on a journal spinning at 50 krpm, the MMFB dynamic direct force coefficients show little frequency dependency, while the BFB stiffness and damping increases with frequency (200–400 Hz). The BFB has a much larger stiffness and viscous damping coefficients than the MMFB. However, the MMFB material loss factor is at least twice as large as that in the BFB. The experiments show that the MMFB, when compared to the BFB, has a lower drag power and earlier lift-off speed and with dynamic force coefficients having a lesser dependency on whirl frequency excitation. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000010 [...] [article] A metal mesh foil bearing and a bump-type foil bearing : comparison of performance for two similar size gas bearings [texte imprimé] / Luis San Andrés, Auteur ; Thomas Abraham Chirathadam, Auteur . - 2012 . - 13 p. gas turbines Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 134 N° 10 (Octobre 2012) . - 13 p. Mots-clés : gas  bearings;  bump-type  foil  bearings  (BFBs);  overleaf-type  foil  bearings Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Gas bearings in oil-free microturbomachinery for gas process applications and power generation (<400 kW) must be reliable and inexpensive, ensuring low drag power and thermal stability. Bump-type foil bearings (BFBs) and overleaf-type foil bearings are in use in specialized applications, though their development time (design and prototyping), exotic materials, and excessive manufacturing cost still prevent their widespread usage. Metal mesh foil bearings (MMFBs), on the other hand, are an inexpensive alternative that use common materials and no restrictions on intellectual property. Laboratory testing shows that prototype MMFBs perform similarly as typical BFBs, but offer significantly larger damping to dissipate mechanical energy due to rotor vibrations. This paper details a one-to-one comparison of the static and dynamic forced performance characteristics of a MMFB against a BFB of similar size and showcases the advantages and disadvantages of MMFBs. The bearings for comparison are a generation I BFB and a MMFB, both with a slenderness ratio L/D = 1.04. Measurements of rotor lift-off speed and drag friction at start-up and airborne conditions were conducted for rotor speeds to 70 krpm and under identical specific loads (W/LD = 0.06 to 0.26 bar). Static load versus bearing elastic deflection tests evidence a typical hardening nonlinearity with mechanical hysteresis, the MMFB showing two to three times more material damping than the BFB. The MMFB exhibits larger drag torques during rotor start-up, and shut-down tests though bearing lift-off happens at lower rotor speeds (~15 krpm). As the rotor becomes airborne, both bearings offer very low drag friction coefficients, ~0.03 for the MMFB and ~0.04 for the BFB in the speed range 20–40 krpm. With the bearings floating on a journal spinning at 50 krpm, the MMFB dynamic direct force coefficients show little frequency dependency, while the BFB stiffness and damping increases with frequency (200–400 Hz). The BFB has a much larger stiffness and viscous damping coefficients than the MMFB. However, the MMFB material loss factor is at least twice as large as that in the BFB. The experiments show that the MMFB, when compared to the BFB, has a lower drag power and earlier lift-off speed and with dynamic force coefficients having a lesser dependency on whirl frequency excitation. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000010 [...]