Documents disponibles écrits par cet auteur

Development of a computer program for the simulation of ice-bank system operation, part II: Verification / Marino Grozdek in International journal of refrigeration, Vol. 33 N° 8 (Décembre 2010) 

Public ISBD [article]  in International journal of refrigeration > Vol. 33 N° 8 (Décembre 2010) . - pp. 1657-1669 Titre : Development of a computer program for the simulation of ice-bank system operation, part II: Verification Titre original : Développement d'un logiciel pour la simulation du fonctionnement d'un système d'accumulation de glace. Partie II : vérification Type de document : texte imprimé Auteurs : Marino Grozdek, Auteur ; Boris Halasz, Auteur ; Tonko Ćurko, Auteur Année de publication : 2011 Article en page(s) : pp. 1657-1669 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Thermal  storage  Ice  bank  Cooling  Milk  Experiment  Modelling  Simulation  Comparison Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : In order to verify the mathematical model of an ice bank system developed for the purpose of predicting the system performance, experimental measurements on the ice bank system were performed. Static, indirect, cool thermal storage system, with an external ice-on-coil building/melting was considered. Cooling energy stored in the form of ice by night is used for the rapid cooling of milk after the process of pasteurization by day. The ice bank system was tested under real operating conditions to determine parameters such as the time-varying heat load imposed by the consumer, refrigeration unit load, storage capacity, supply water temperature to the load and to find charging and discharging characteristics of the storage. Experimentally obtained results were then compared to the computed ones. It was found that the calculated and experimentally obtained results are in good agreement as long as there is ice present in the silo. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700710000885 [article] Development of a computer program for the simulation of ice-bank system operation, part II: Verification = Développement d'un logiciel pour la simulation du fonctionnement d'un système d'accumulation de glace. Partie II : vérification [texte imprimé] / Marino Grozdek, Auteur ; Boris Halasz, Auteur ; Tonko Ćurko, Auteur . - 2011 . - pp. 1657-1669. Génie Mécanique Langues : Anglais (eng) in International journal of refrigeration > Vol. 33 N° 8 (Décembre 2010) . - pp. 1657-1669 Mots-clés : Thermal  storage  Ice  bank  Cooling  Milk  Experiment  Modelling  Simulation  Comparison Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : In order to verify the mathematical model of an ice bank system developed for the purpose of predicting the system performance, experimental measurements on the ice bank system were performed. Static, indirect, cool thermal storage system, with an external ice-on-coil building/melting was considered. Cooling energy stored in the form of ice by night is used for the rapid cooling of milk after the process of pasteurization by day. The ice bank system was tested under real operating conditions to determine parameters such as the time-varying heat load imposed by the consumer, refrigeration unit load, storage capacity, supply water temperature to the load and to find charging and discharging characteristics of the storage. Experimentally obtained results were then compared to the computed ones. It was found that the calculated and experimentally obtained results are in good agreement as long as there is ice present in the silo. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700710000885

On the numerical prediction of finite length squeeze film dampers performance with free air entrainment / Tilmer H. Méndez in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 132 N° 1 (Janvier 2010) . - 07 p. Titre : On the numerical prediction of finite length squeeze film dampers performance with free air entrainment Type de document : texte imprimé Auteurs : Tilmer H. Méndez, Auteur ; Tonko Ćurko, Auteur ; Marco A. Ciaccia, Auteur Année de publication : 2010 Article en page(s) : 07 p. Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Cavitation  Compressible  flow  Density  Finite  volume  methods  Fracture  Machine  bearings  Machine  control  Rotors  Stratified  flow  Turbomachinery  Vibration  control  Viscosity Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Squeeze film dampers (SFDs) are commonly used in turbomachinery to dampen shaft vibrations in rotor-bearing systems. The main factor deterring the success of analytical models for the prediction of SFD's performance lies on the modeling of dynamic film rupture. Usually, the cavitation models developed for journal bearings are applied to SFDs. Yet, the characteristic motion of the SFD results in the entrapment of air into the oil film, producing a bubbly mixture that cannot be represented by these models. There is a need to identify and understand the parameters that affect air entrainment and subsequent formation of a bubbly air-oil mixture within the lubricant film. A previous model by and Diazand San Andrés (2001, “A Model for Squeeze Film Dampers Operating With Air Entrapment and Validation With Experiments,” ASME J. Tribol., 123, pp. 125–133) advanced estimation of the amount of film-entrapped air based on a nondimensional number that related both geometrical and operating parameters but limited to the short bearing approximation (i.e., neglecting circumferential flow). The present study extends their work to consider the effects of finite length-to-diameter ratios. This is achieved by means of a finite volume integration of the two-dimensional, Newtonian, compressible Reynolds equation combined with the effective mixture density and viscosity defined in the work of Diaz and San Andrés. A flow balance at the open end of the film is devised to estimate the amount of air entrapped within the film. The results show, in dimensionless plots, a map of the amount of entrained air as a function of the feed-squeeze flow number, defined by Diaz and San Andrés, and the length-to-diameter ratio of the damper. Entrained air is shown to decrease as the L/D ratio increases, going from the approximate solution of Diaz and San Andrés for infinitely short SFDs down to no air entrainment for an infinite length SFD. The results of this research are of immediate engineering applicability. Furthermore, they represent a firm step to advance the understanding of the effects of air entrapment on the performance of SFDs. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000132000001 [...] [article] On the numerical prediction of finite length squeeze film dampers performance with free air entrainment [texte imprimé] / Tilmer H. Méndez, Auteur ; Tonko Ćurko, Auteur ; Marco A. Ciaccia, 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° 1 (Janvier 2010) . - 07 p. Mots-clés : Cavitation  Compressible  flow  Density  Finite  volume  methods  Fracture  Machine  bearings  Machine  control  Rotors  Stratified  flow  Turbomachinery  Vibration  control  Viscosity Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Squeeze film dampers (SFDs) are commonly used in turbomachinery to dampen shaft vibrations in rotor-bearing systems. The main factor deterring the success of analytical models for the prediction of SFD's performance lies on the modeling of dynamic film rupture. Usually, the cavitation models developed for journal bearings are applied to SFDs. Yet, the characteristic motion of the SFD results in the entrapment of air into the oil film, producing a bubbly mixture that cannot be represented by these models. There is a need to identify and understand the parameters that affect air entrainment and subsequent formation of a bubbly air-oil mixture within the lubricant film. A previous model by and Diazand San Andrés (2001, “A Model for Squeeze Film Dampers Operating With Air Entrapment and Validation With Experiments,” ASME J. Tribol., 123, pp. 125–133) advanced estimation of the amount of film-entrapped air based on a nondimensional number that related both geometrical and operating parameters but limited to the short bearing approximation (i.e., neglecting circumferential flow). The present study extends their work to consider the effects of finite length-to-diameter ratios. This is achieved by means of a finite volume integration of the two-dimensional, Newtonian, compressible Reynolds equation combined with the effective mixture density and viscosity defined in the work of Diaz and San Andrés. A flow balance at the open end of the film is devised to estimate the amount of air entrapped within the film. The results show, in dimensionless plots, a map of the amount of entrained air as a function of the feed-squeeze flow number, defined by Diaz and San Andrés, and the length-to-diameter ratio of the damper. Entrained air is shown to decrease as the L/D ratio increases, going from the approximate solution of Diaz and San Andrés for infinitely short SFDs down to no air entrainment for an infinite length SFD. The results of this research are of immediate engineering applicability. Furthermore, they represent a firm step to advance the understanding of the effects of air entrapment on the performance of SFDs. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000132000001 [...]

Rate-distortion optimization of scalable video codecs / Hoda Roodaki in Signal processing. Image communication, Vol. 25 N° 4 (Avril 2010) 

Public ISBD [article]  in Signal processing. Image communication > Vol. 25 N° 4 (Avril 2010) . - pp. 276–286 Titre : Rate-distortion optimization of scalable video codecs Type de document : texte imprimé Auteurs : Hoda Roodaki, Auteur ; Tonko Ćurko, Auteur ; Mohammad Ghanbari, Auteur Année de publication : 2012 Article en page(s) : pp. 276–286 Note générale : Electronique Langues : Anglais (eng) Mots-clés : Rate-distortion  optimization  Scalable  video  coding Résumé : In this paper joint optimization of layers in the layered video coding is investigated. Through theoretical analysis and simulations, it is shown that, due to higher interactions between the layers in a SNR scalable codec, this type of layering technique benefits most from joint optimization of the layers. A method for joint optimization is then proposed, and its compression efficiency is contrasted against the separate optimization and an optimized single layer coder. It is shown that, in joint optimization of SNR scalable coders when the quantization step size of the enhancement layer is larger than half the step size of the base layer, an additional improvement is gained by not sending the enhancement zero valued quantized coefficients, provided they are quantized at the base-layer. This will result in a non-standard bitstream syntax and as an alternative for standard syntax, one may skip the inter coded enhancement macroblocks. Through extensive tests it is shown that while separate optimization of SNR coders is inferior to single layer coder by more than 2 dB, with joint optimization this gap is reduced to 0.3–0.5 dB. We have shown that through joint optimization quality of the base layer video is also improved over the separate optimization. It is also shown that spatial scalability like SNR scalability does benefit from joint optimization, though not being able to exploit the relation between the quantizer step sizes. The amount of improvement depends on the interpolation artifacts of upsampled base-layer and the residual quantization distortion of this layer. Hence, the degree of improvement depends on image contents as well as the bit rate budget. Simulation results show that joint optimization of spatial scalable coders is about 0.5–1 dB inferior to the single layer optimized coder, where its separate optimization counterpart like SNR scalability is more than 2 dB worse. ISSN : 0923-5965 En ligne : http://www.sciencedirect.com/science/article/pii/S0923596510000056 [article] Rate-distortion optimization of scalable video codecs [texte imprimé] / Hoda Roodaki, Auteur ; Tonko Ćurko, Auteur ; Mohammad Ghanbari, Auteur . - 2012 . - pp. 276–286. Electronique Langues : Anglais (eng) in Signal processing. Image communication > Vol. 25 N° 4 (Avril 2010) . - pp. 276–286 Mots-clés : Rate-distortion  optimization  Scalable  video  coding Résumé : In this paper joint optimization of layers in the layered video coding is investigated. Through theoretical analysis and simulations, it is shown that, due to higher interactions between the layers in a SNR scalable codec, this type of layering technique benefits most from joint optimization of the layers. A method for joint optimization is then proposed, and its compression efficiency is contrasted against the separate optimization and an optimized single layer coder. It is shown that, in joint optimization of SNR scalable coders when the quantization step size of the enhancement layer is larger than half the step size of the base layer, an additional improvement is gained by not sending the enhancement zero valued quantized coefficients, provided they are quantized at the base-layer. This will result in a non-standard bitstream syntax and as an alternative for standard syntax, one may skip the inter coded enhancement macroblocks. Through extensive tests it is shown that while separate optimization of SNR coders is inferior to single layer coder by more than 2 dB, with joint optimization this gap is reduced to 0.3–0.5 dB. We have shown that through joint optimization quality of the base layer video is also improved over the separate optimization. It is also shown that spatial scalability like SNR scalability does benefit from joint optimization, though not being able to exploit the relation between the quantizer step sizes. The amount of improvement depends on the interpolation artifacts of upsampled base-layer and the residual quantization distortion of this layer. Hence, the degree of improvement depends on image contents as well as the bit rate budget. Simulation results show that joint optimization of spatial scalable coders is about 0.5–1 dB inferior to the single layer optimized coder, where its separate optimization counterpart like SNR scalability is more than 2 dB worse. ISSN : 0923-5965 En ligne : http://www.sciencedirect.com/science/article/pii/S0923596510000056