Documents disponibles écrits par cet auteur

On occurrence of reverse full annular rub / John J. Yu 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 : On occurrence of reverse full annular rub Type de document : texte imprimé Auteurs : John J. Yu, Auteur Année de publication : 2012 Article en page(s) : 08 p. Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Friction  Mechanical  contact  Polynomials  Rotors  Seals  (stoppers) Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : This paper discusses reverse full annular rub based on a two degree-of-freedom rotor/seal model where a rubbing location can be simulated away from the lumped rotor mass. The analytical model is much closer to the experimental setup for comparison of results, and real machines for analysis, than the previous one degree-of-freedom model. Its closed-form solution is given including reverse rub amplitudes and relative phases, as well as the normal contact force. The exact frequency equation in polynomial form yields reverse full annular rub frequencies without having to neglect any parameters. Many conclusions can be drawn directly from explicit expressions without numerical calculations. The solution with nonpositive normal contact force indicates a dry-friction whirl/whip-free region, usually accompanied by low friction and/or high damping. The analytical study covers both dry-friction whirl and dry-friction whip, and their relations with dry-friction factor, damping, and rotor speed. Range of reverse rub frequencies, their relation with rotor and rotor/seal coupled natural frequencies, and direction of frictional force, are also revealed. Destructive dry-friction whip experimental results are given, which have fully confirmed the analytical formulas. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000001 [...] [article] On occurrence of reverse full annular rub [texte imprimé] / John J. Yu, 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 : Friction  Mechanical  contact  Polynomials  Rotors  Seals  (stoppers) Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : This paper discusses reverse full annular rub based on a two degree-of-freedom rotor/seal model where a rubbing location can be simulated away from the lumped rotor mass. The analytical model is much closer to the experimental setup for comparison of results, and real machines for analysis, than the previous one degree-of-freedom model. Its closed-form solution is given including reverse rub amplitudes and relative phases, as well as the normal contact force. The exact frequency equation in polynomial form yields reverse full annular rub frequencies without having to neglect any parameters. Many conclusions can be drawn directly from explicit expressions without numerical calculations. The solution with nonpositive normal contact force indicates a dry-friction whirl/whip-free region, usually accompanied by low friction and/or high damping. The analytical study covers both dry-friction whirl and dry-friction whip, and their relations with dry-friction factor, damping, and rotor speed. Range of reverse rub frequencies, their relation with rotor and rotor/seal coupled natural frequencies, and direction of frictional force, are also revealed. Destructive dry-friction whip experimental results are given, which have fully confirmed the analytical formulas. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000001 [...]

Onset of (1/2)X vibration and its prevention / John J. Yu in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 132 N° 2 (Fevrier 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 132 N° 2 (Fevrier 2010) . - 10 p. Titre : Onset of (1/2)X vibration and its prevention Type de document : texte imprimé Auteurs : John J. Yu, Auteur Année de publication : 2010 Article en page(s) : 10 p. Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Turbomachinery  Vibrations Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : This paper discusses real cases on three different machines where subsynchronous vibration occurred suddenly at a frequency exactly equal to one-half ((1/2)X) of the operational speed of 3600 rpm. In two cases, vibration amplitude increased from around 2 mils (51 µm) pp to over 12 mils (305 µm) pp, causing the machine to trip unexpectedly. The (1/2)X vibration was even sustained during shutdown at speed below 3600 rpm after trip. Unlike other reported experimental results, shaft orbit measured by proximity probes was fairly circular and dominantly composed of the (1/2)X component without significant components at multiple orders of the (1/2)X. The onset of the subsynchronous (1/2)X vibration was sometimes triggered by changes in bearing lube oil temperature and supply pressure, which would typically be believed to be caused by oil whirl that could occur at close to the (1/2)X frequency. An upward shift in shaft centerline plot was observed to occur prior to the onset of the subsynchronous vibration. The (1/2)X vibration was successfully prevented by changing bearing clearance or adjustment of bearing oil temperature and supply pressure. Parametric excitation analysis on (1/2)X vibration is also given in this paper. The main purpose of this paper, unlike previously published papers on analytical or experimental results, is to show shaft orbital and centerline plots as well as spectrum data due to the (1/2)X vibration, including effects of operating conditions in real rotating machines. DEWEY : 62.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000132000002 [...] [article] Onset of (1/2)X vibration and its prevention [texte imprimé] / John J. Yu, Auteur . - 2010 . - 10 p. Génie Mécanique Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 132 N° 2 (Fevrier 2010) . - 10 p. Mots-clés : Turbomachinery  Vibrations Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : This paper discusses real cases on three different machines where subsynchronous vibration occurred suddenly at a frequency exactly equal to one-half ((1/2)X) of the operational speed of 3600 rpm. In two cases, vibration amplitude increased from around 2 mils (51 µm) pp to over 12 mils (305 µm) pp, causing the machine to trip unexpectedly. The (1/2)X vibration was even sustained during shutdown at speed below 3600 rpm after trip. Unlike other reported experimental results, shaft orbit measured by proximity probes was fairly circular and dominantly composed of the (1/2)X component without significant components at multiple orders of the (1/2)X. The onset of the subsynchronous (1/2)X vibration was sometimes triggered by changes in bearing lube oil temperature and supply pressure, which would typically be believed to be caused by oil whirl that could occur at close to the (1/2)X frequency. An upward shift in shaft centerline plot was observed to occur prior to the onset of the subsynchronous vibration. The (1/2)X vibration was successfully prevented by changing bearing clearance or adjustment of bearing oil temperature and supply pressure. Parametric excitation analysis on (1/2)X vibration is also given in this paper. The main purpose of this paper, unlike previously published papers on analytical or experimental results, is to show shaft orbital and centerline plots as well as spectrum data due to the (1/2)X vibration, including effects of operating conditions in real rotating machines. DEWEY : 62.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000132000002 [...]