Documents disponibles écrits par cet auteur

Improvement of the performance of a centrifugal compressor by modifying the volute inlet / Semi Kim in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 07 p. Titre : Improvement of the performance of a centrifugal compressor by modifying the volute inlet Type de document : texte imprimé Auteurs : Semi Kim, Auteur ; Park, Junyoung, Auteur ; Kukyoung Ahn, Auteur Année de publication : 2011 Article en page(s) : 07 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  separation  (technology);  compressors;  impellers;  diffusers;  design Résumé : In centrifugal compressors, the diffuser and the volute have strong influences on the flow discharged from the impeller and thus also on the performance. In particular, a key parameter is the radial velocity at the volute inlet; it determines the swirl velocity, which is dissipated as a loss, i.e., it results in performance degradation. With the aim of reducing the swirl loss, a new type of volute with a modified inlet height was tested in this study. The volute inlet height was modified to 6 mm and 7 mm from the original height of 5 mm. The reliability of our computations was tested by comparison of the results of a model with this original height with experimental data. Flow analyses were conducted not only at the design mass flow rate but also at lower and higher mass flow rates. A higher total-to-total efficiency was obtained as a result of the linear increases of the volute inlet height from the diffuser outlet to 6 mm and 7 mm. Our detailed investigation of the simulated flow fields shows that the flow characteristics for a volute inlet height of 6 mm are better than those for a volute inlet height of 5 mm. These results clearly show that a greater volute inlet height assists in pressure recovery and reduces swirl loss in the volute. However, the volute inlet height of 7 mm results in larger hub separation and more energy loss, and thus in inferior performance. Therefore, the hub separation and the radial velocity at the volute inlet strongly influence the performance. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Improvement of the performance of a centrifugal compressor by modifying the volute inlet [texte imprimé] / Semi Kim, Auteur ; Park, Junyoung, Auteur ; Kukyoung Ahn, Auteur . - 2011 . - 07 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 07 p. Mots-clés : pressure;  flow  (dynamics);  separation  (technology);  compressors;  impellers;  diffusers;  design Résumé : In centrifugal compressors, the diffuser and the volute have strong influences on the flow discharged from the impeller and thus also on the performance. In particular, a key parameter is the radial velocity at the volute inlet; it determines the swirl velocity, which is dissipated as a loss, i.e., it results in performance degradation. With the aim of reducing the swirl loss, a new type of volute with a modified inlet height was tested in this study. The volute inlet height was modified to 6 mm and 7 mm from the original height of 5 mm. The reliability of our computations was tested by comparison of the results of a model with this original height with experimental data. Flow analyses were conducted not only at the design mass flow rate but also at lower and higher mass flow rates. A higher total-to-total efficiency was obtained as a result of the linear increases of the volute inlet height from the diffuser outlet to 6 mm and 7 mm. Our detailed investigation of the simulated flow fields shows that the flow characteristics for a volute inlet height of 6 mm are better than those for a volute inlet height of 5 mm. These results clearly show that a greater volute inlet height assists in pressure recovery and reduces swirl loss in the volute. However, the volute inlet height of 7 mm results in larger hub separation and more energy loss, and thus in inferior performance. Therefore, the hub separation and the radial velocity at the volute inlet strongly influence the performance. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Magnetically suspended VSCMGs for simultaneous attitude control and power transfer IPAC service / Park, Junyoung in Transactions of the ASME . Journal of dynamic systems, measurement, and control, Vol. 132 N° 5 (Septembre 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of dynamic systems, measurement, and control > Vol. 132 N° 5 (Septembre 2010) . - 15 p. Titre : Magnetically suspended VSCMGs for simultaneous attitude control and power transfer IPAC service Type de document : texte imprimé Auteurs : Park, Junyoung, Auteur ; Palazzolo, Alan, Auteur Année de publication : 2010 Article en page(s) : 15 p. Note générale : Systèmes dynamiques Langues : Anglais (eng) Mots-clés : Artificial  satellites  Attitude  control  Gyroscopes  Velocity  control  Vibrations  Wheels Index. décimale : 629.8 Résumé : This paper presents the theory and numerical results of utilizing four gimbaled, magnetically suspended, variable speed flywheels for simultaneous satellite attitude control and power transfer (charge, storage, and delivery). Previous variable speed control moment gyro models and control algorithms assumed that the flywheel bearings were rigid. However, high speed flywheels on spacecraft will be supported by active magnetic bearings, which have flexibility and in general frequency dependent characteristics. The present work provides the theory for modeling the satellite and flywheel systems including controllers for stable magnetic bearing suspension for power transfer to and from the flywheels and for attitude control of the satellite. A major reason for utilizing flexible bearings is to isolate the imbalance disturbance forces from the flywheel to the satellite. This g-jitter vibration could interfere with the operation of sensitive onboard instrumentation. A special control approach is employed for the magnetic bearings to reject the imbalance disturbances. The stability, robustness, tracking, and disturbance rejection performances of the feedback control laws are demonstrated with a satellite simulation that includes initial attitude error, system modeling error, and flywheel imbalance disturbance. DEWEY : 629.8 ISSN : 0022-0434 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JDSMAA00013200 [...] [article] Magnetically suspended VSCMGs for simultaneous attitude control and power transfer IPAC service [texte imprimé] / Park, Junyoung, Auteur ; Palazzolo, Alan, Auteur . - 2010 . - 15 p. Systèmes dynamiques Langues : Anglais (eng) in Transactions of the ASME . Journal of dynamic systems, measurement, and control > Vol. 132 N° 5 (Septembre 2010) . - 15 p. Mots-clés : Artificial  satellites  Attitude  control  Gyroscopes  Velocity  control  Vibrations  Wheels Index. décimale : 629.8 Résumé : This paper presents the theory and numerical results of utilizing four gimbaled, magnetically suspended, variable speed flywheels for simultaneous satellite attitude control and power transfer (charge, storage, and delivery). Previous variable speed control moment gyro models and control algorithms assumed that the flywheel bearings were rigid. However, high speed flywheels on spacecraft will be supported by active magnetic bearings, which have flexibility and in general frequency dependent characteristics. The present work provides the theory for modeling the satellite and flywheel systems including controllers for stable magnetic bearing suspension for power transfer to and from the flywheels and for attitude control of the satellite. A major reason for utilizing flexible bearings is to isolate the imbalance disturbance forces from the flywheel to the satellite. This g-jitter vibration could interfere with the operation of sensitive onboard instrumentation. A special control approach is employed for the magnetic bearings to reject the imbalance disturbances. The stability, robustness, tracking, and disturbance rejection performances of the feedback control laws are demonstrated with a satellite simulation that includes initial attitude error, system modeling error, and flywheel imbalance disturbance. DEWEY : 629.8 ISSN : 0022-0434 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JDSMAA00013200 [...]

MIMO active vibration control of magnetically suspended flywheels for satellite IPAC service / Park, Junyoung in Transactions of the ASME . Journal of dynamic systems, measurement, and control, Vol. 130 n°4 (Juillet 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of dynamic systems, measurement, and control > Vol. 130 n°4 (Juillet 2008) . - 22 p. Titre : MIMO active vibration control of magnetically suspended flywheels for satellite IPAC service Type de document : texte imprimé Auteurs : Park, Junyoung, Auteur ; Raymond Beach, Auteur ; Palazzolo, Alan, Auteur Année de publication : 2008 Article en page(s) : 22 p. Note générale : dynamic systems Langues : Anglais (eng) Mots-clés : force;  motion;  flywheels;  satellites Résumé : Theory and simulation results have demonstrated that four, variable speed flywheels could potentially provide the energy storage and attitude control functions of existing batteries and control moment gyros on a satellite. Past modeling and control algorithms were based on the assumption of rigidity in the flywheel’s bearings and the satellite structure. This paper provides simulation results and theory, which eliminates this assumption utilizing control algorithms for active vibration control (AVC), flywheel shaft levitation, and integrated power transfer and attitude control (IPAC), that are effective even with low stiffness active magnetic bearings (AMBs) and flexible satellite appendages. The flywheel AVC and levitation tasks are provided by a multiple input–multiple output control law that enhances stability by reducing the dependence of the forward and backward gyroscopic poles with changes in flywheel speed. The control law is shown to be effective even for (1) large polar to transverse inertia ratios, which increases the stored energy density while causing the poles to become more speed dependent, and for (2) low bandwidth controllers shaped to suppress high frequency noise. Passive vibration dampers are designed to reduce the vibrations of flexible appendages of the satellite. Notch, low-pass, and bandpass filters are implemented in the AMB system to reduce and cancel high frequency, dynamic bearing forces and motor torques due to flywheel mass imbalance. Successful IPAC simulation results are presented with a 12% initial attitude error, large polar to transverse inertia ratio (IP∕IT), structural flexibility, and unbalance mass disturbance. En ligne : http://dynamicsystems.asmedigitalcollection.asme.org/issue.aspx?journalid=117&is [...] [article] MIMO active vibration control of magnetically suspended flywheels for satellite IPAC service [texte imprimé] / Park, Junyoung, Auteur ; Raymond Beach, Auteur ; Palazzolo, Alan, Auteur . - 2008 . - 22 p. dynamic systems Langues : Anglais (eng) in Transactions of the ASME . Journal of dynamic systems, measurement, and control > Vol. 130 n°4 (Juillet 2008) . - 22 p. Mots-clés : force;  motion;  flywheels;  satellites Résumé : Theory and simulation results have demonstrated that four, variable speed flywheels could potentially provide the energy storage and attitude control functions of existing batteries and control moment gyros on a satellite. Past modeling and control algorithms were based on the assumption of rigidity in the flywheel’s bearings and the satellite structure. This paper provides simulation results and theory, which eliminates this assumption utilizing control algorithms for active vibration control (AVC), flywheel shaft levitation, and integrated power transfer and attitude control (IPAC), that are effective even with low stiffness active magnetic bearings (AMBs) and flexible satellite appendages. The flywheel AVC and levitation tasks are provided by a multiple input–multiple output control law that enhances stability by reducing the dependence of the forward and backward gyroscopic poles with changes in flywheel speed. The control law is shown to be effective even for (1) large polar to transverse inertia ratios, which increases the stored energy density while causing the poles to become more speed dependent, and for (2) low bandwidth controllers shaped to suppress high frequency noise. Passive vibration dampers are designed to reduce the vibrations of flexible appendages of the satellite. Notch, low-pass, and bandpass filters are implemented in the AMB system to reduce and cancel high frequency, dynamic bearing forces and motor torques due to flywheel mass imbalance. Successful IPAC simulation results are presented with a 12% initial attitude error, large polar to transverse inertia ratio (IP∕IT), structural flexibility, and unbalance mass disturbance. En ligne : http://dynamicsystems.asmedigitalcollection.asme.org/issue.aspx?journalid=117&is [...]