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Auteur Jun Zhang |
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Ajouter le résultat dans votre panier Faire une suggestion Affiner la rechercheCalculation of moisture distribution in early-age concrete / Jun Zhang in Journal of engineering mechanics, Vol. 135 N° 8 (Août 2009)
Titre : Calculation of moisture distribution in early-age concrete Type de document : texte imprimé Auteurs : Jun Zhang, Auteur ; Qi, Kun, Auteur ; Yu Huang, Auteur Article en page(s) : pp. 871-880 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Concrete Aging Moisture Humidity. Résumé : The moisture content in concrete pores is a critical parameter for most of the degradation processes suffered by concrete, such as concrete shrinkage and related cracking. The objective of this paper is to present the formulation of a general moisture distribution model for young-age concrete. In the modeling, both cement hydration and moisture diffusion resulted humidity variations are taken into account synchronously. The effect of initial water distribution (after concrete casting) on the development of moisture distribution is considered by introducing a critical time parameter. The simulation of humidity reduction produced from self-desiccation is based on cement hydration degree that taking the effect of temperature into account by using the equilibrant age concept. During modeling the moisture diffusion, a multilinear model was adopted to simulate the moisture dependent diffusivity. The developed model and finite deferential method can well predict the moisture distribution as well as its variations with time. Good agreement between model predictions and experimental results is found. These results can subsequently be used in shrinkage induced stress field analyses, and further be used for cracking control of concrete structures. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JENMDT&smode=strres [...]
in Journal of engineering mechanics > Vol. 135 N° 8 (Août 2009) . - pp. 871-880[article] Calculation of moisture distribution in early-age concrete [texte imprimé] / Jun Zhang, Auteur ; Qi, Kun, Auteur ; Yu Huang, Auteur . - pp. 871-880.
Mécanique appliquée
Langues : Anglais (eng)
in Journal of engineering mechanics > Vol. 135 N° 8 (Août 2009) . - pp. 871-880
Mots-clés : Concrete Aging Moisture Humidity. Résumé : The moisture content in concrete pores is a critical parameter for most of the degradation processes suffered by concrete, such as concrete shrinkage and related cracking. The objective of this paper is to present the formulation of a general moisture distribution model for young-age concrete. In the modeling, both cement hydration and moisture diffusion resulted humidity variations are taken into account synchronously. The effect of initial water distribution (after concrete casting) on the development of moisture distribution is considered by introducing a critical time parameter. The simulation of humidity reduction produced from self-desiccation is based on cement hydration degree that taking the effect of temperature into account by using the equilibrant age concept. During modeling the moisture diffusion, a multilinear model was adopted to simulate the moisture dependent diffusivity. The developed model and finite deferential method can well predict the moisture distribution as well as its variations with time. Good agreement between model predictions and experimental results is found. These results can subsequently be used in shrinkage induced stress field analyses, and further be used for cracking control of concrete structures. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JENMDT&smode=strres [...] Exemplaires
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Titre : A direct-flux-vector-controlled induction generator with space-vector modulation for integrated starter alternator Type de document : texte imprimé Auteurs : Jun Zhang, Auteur ; Muhammed Fazlur Rahman, Auteur Année de publication : 2007 Article en page(s) : 2512-2520 p. Note générale : Electronique Langues : Anglais (eng) Mots-clés : Direct-flux vector control (DFC) Induction machine Integrated starter alternator (ISA) Space-vector modulation (SVM) 42-V PowerNet Commande de vecteur directe flux Machine à induction Alternateur intégré démarreur Modulation d'espace Index. décimale : 621 Ingénierie mécanique en général. Technologie nucléaire. Ingénierie électrique. Machinerie Résumé : A direct-flux-vector-controlled scheme of induction generator has been proposed in this paper for future 42-V automobile application. The fundamental relationship between the rotating speed of the stator flux vector and torque is analyzed. A simple structure with only one proportional-integral (PI) controller is shown to implement the torque and flux controls adequately. By controlling the electromagnetic torque of the induction machine, the required dc-bus voltage can be well regulated within the 42-V PowerNet specifications. Fixed switching frequency and low torque ripple are obtained with space-vector modulation technique. Simulation and experimental results indicate that the proposed scheme provides a practical solution for an integrated starter alternator other than the widely applied field-oriented- control scheme.
On a proposé un arrangement diriger-flux-vecteur-commandé de générateur d'induction en ce document pour la future application de l'automobile 42-V. Le rapport fondamental entre la vitesse tournante du vecteur de flux de redresseur et le couple est analysé. Une structure simple avec seulement un contrôleur (pi) proportionnel-intégral est montrée pour mettre en application les commandes de couple et de flux en juste proportion. En commandant le couple électromagnétique de la machine d'induction, la tension exigée de C.C-autobus peut être bien réglée selon les caractéristiques de 42-V PowerNet. La fréquence fixe de commutation et la basse ondulation de couple sont obtenues avec la technique de modulation d'espace-vecteur. La simulation et les résultats expérimentaux indiquent que l'arrangement proposé fournit une solution pratique pour un alternateur intégré de démarreur autre que l'arrangement de commande champ-orienté largement appliqué.DEWEY : 621 ISSN : 0278-0046 RAMEAU : Analyse vectorielle-- Automobiles -- Alternateurs En ligne : http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?isnumber=4282101&arnumber=4285716 [...]
in IEEE transactions on industrial electronics > Vol. 54 N°5 (Octobre 2007) . - 2512-2520 p.[article] A direct-flux-vector-controlled induction generator with space-vector modulation for integrated starter alternator [texte imprimé] / Jun Zhang, Auteur ; Muhammed Fazlur Rahman, Auteur . - 2007 . - 2512-2520 p.
Electronique
Langues : Anglais (eng)
in IEEE transactions on industrial electronics > Vol. 54 N°5 (Octobre 2007) . - 2512-2520 p.
Mots-clés : Direct-flux vector control (DFC) Induction machine Integrated starter alternator (ISA) Space-vector modulation (SVM) 42-V PowerNet Commande de vecteur directe flux Machine à induction Alternateur intégré démarreur Modulation d'espace Index. décimale : 621 Ingénierie mécanique en général. Technologie nucléaire. Ingénierie électrique. Machinerie Résumé : A direct-flux-vector-controlled scheme of induction generator has been proposed in this paper for future 42-V automobile application. The fundamental relationship between the rotating speed of the stator flux vector and torque is analyzed. A simple structure with only one proportional-integral (PI) controller is shown to implement the torque and flux controls adequately. By controlling the electromagnetic torque of the induction machine, the required dc-bus voltage can be well regulated within the 42-V PowerNet specifications. Fixed switching frequency and low torque ripple are obtained with space-vector modulation technique. Simulation and experimental results indicate that the proposed scheme provides a practical solution for an integrated starter alternator other than the widely applied field-oriented- control scheme.
On a proposé un arrangement diriger-flux-vecteur-commandé de générateur d'induction en ce document pour la future application de l'automobile 42-V. Le rapport fondamental entre la vitesse tournante du vecteur de flux de redresseur et le couple est analysé. Une structure simple avec seulement un contrôleur (pi) proportionnel-intégral est montrée pour mettre en application les commandes de couple et de flux en juste proportion. En commandant le couple électromagnétique de la machine d'induction, la tension exigée de C.C-autobus peut être bien réglée selon les caractéristiques de 42-V PowerNet. La fréquence fixe de commutation et la basse ondulation de couple sont obtenues avec la technique de modulation d'espace-vecteur. La simulation et les résultats expérimentaux indiquent que l'arrangement proposé fournit une solution pratique pour un alternateur intégré de démarreur autre que l'arrangement de commande champ-orienté largement appliqué.DEWEY : 621 ISSN : 0278-0046 RAMEAU : Analyse vectorielle-- Automobiles -- Alternateurs En ligne : http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?isnumber=4282101&arnumber=4285716 [...] Exemplaires
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Titre : Engineered cementitious composite with characteristic of low drying shrinkage Type de document : texte imprimé Auteurs : Jun Zhang, Auteur ; Chengxu Gong, Auteur ; Zili Guo, Auteur Année de publication : 2009 Article en page(s) : pp. 303–312 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Tensile properties Shrinkage Composite Fiber reinforcement Résumé : This paper reports a new class of engineered cementitious composite (ECC) with characteristics of low drying shrinkage, tight crack opening and high tensile strain capacity. Research emphasis is placed on the influence of different cementitious matrix on drying shrinkage, tensile property and early age cracking behavior of the composites. Experimental results show that drying shrinkage of the composite is greatly reduced as using the low shrinkage cementitious material in matrix, while the composite remains strain-hardening and multiple cracking characteristics. The measured drying shrinkage strain at 28 days is only 109 × 10− 6 to 242 × 10− 6 for low shrinkage ECCs. For traditional ECC, the shrinkage strain at 28 days is nearly 1200 × 10− 6. The average tensile strain capacity after 28 days curing is 2.5% of the low shrinkage ECC with tensile strength of 4–5 MPa. Further, in the strain-hardening and multiple cracking stage, cracks with much smaller width compared to the traditional ECC are formed in the low shrinkage ECC. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000398
in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 303–312[article] Engineered cementitious composite with characteristic of low drying shrinkage [texte imprimé] / Jun Zhang, Auteur ; Chengxu Gong, Auteur ; Zili Guo, Auteur . - 2009 . - pp. 303–312.
Génie Civil
Langues : Anglais (eng)
in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 303–312
Mots-clés : Tensile properties Shrinkage Composite Fiber reinforcement Résumé : This paper reports a new class of engineered cementitious composite (ECC) with characteristics of low drying shrinkage, tight crack opening and high tensile strain capacity. Research emphasis is placed on the influence of different cementitious matrix on drying shrinkage, tensile property and early age cracking behavior of the composites. Experimental results show that drying shrinkage of the composite is greatly reduced as using the low shrinkage cementitious material in matrix, while the composite remains strain-hardening and multiple cracking characteristics. The measured drying shrinkage strain at 28 days is only 109 × 10− 6 to 242 × 10− 6 for low shrinkage ECCs. For traditional ECC, the shrinkage strain at 28 days is nearly 1200 × 10− 6. The average tensile strain capacity after 28 days curing is 2.5% of the low shrinkage ECC with tensile strength of 4–5 MPa. Further, in the strain-hardening and multiple cracking stage, cracks with much smaller width compared to the traditional ECC are formed in the low shrinkage ECC. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000398 Exemplaires
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Titre : Flyback-based single-stage power-factor-correction scheme with time-multiplexing control Type de document : texte imprimé Auteurs : Jun Zhang, Auteur ; Lu, Dylan Dah-Chuan, Auteur ; Ting, Sun, Auteur Article en page(s) : pp. 1041 - 1049 Note générale : Génie électrique Langues : Anglais (eng) Mots-clés : AC-DC converter Power factor correction (PFC) Single stage Index. décimale : 621.38 Dispositifs électroniques. Tubes à électrons. Photocellules. Accélérateurs de particules. Tubes à rayons X Résumé : A flyback-based single-stage power-factor-correction scheme with time-multiplexing control (TMC) is proposed. As a portion of the input power will be transferred to the output after the first power processing to improve the conversion efficiency, the output voltage would contain substantial low-frequency ripple. An isolated auxiliary circuit based on forward topology is therefore added to the converter to serve as a buffer and a ripple suppression circuit. With TMC, all the power processes can be achieved by a single transformer to lower the size and cost of the converter. In addition, the proposed converter inherits bulk capacitor (auxiliary) voltage clamping capability. The experimental results confirmed the effectiveness of the proposed scheme with high power factor, natural bulk capacitor (auxiliary) clamping voltage, and tight output regulation. DEWEY : 621.38 ISSN : 0278-0046 En ligne : http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5196760
in IEEE transactions on industrial electronics > Vol. 57 N° 3 (Mars 2010) . - pp. 1041 - 1049[article] Flyback-based single-stage power-factor-correction scheme with time-multiplexing control [texte imprimé] / Jun Zhang, Auteur ; Lu, Dylan Dah-Chuan, Auteur ; Ting, Sun, Auteur . - pp. 1041 - 1049.
Génie électrique
Langues : Anglais (eng)
in IEEE transactions on industrial electronics > Vol. 57 N° 3 (Mars 2010) . - pp. 1041 - 1049
Mots-clés : AC-DC converter Power factor correction (PFC) Single stage Index. décimale : 621.38 Dispositifs électroniques. Tubes à électrons. Photocellules. Accélérateurs de particules. Tubes à rayons X Résumé : A flyback-based single-stage power-factor-correction scheme with time-multiplexing control (TMC) is proposed. As a portion of the input power will be transferred to the output after the first power processing to improve the conversion efficiency, the output voltage would contain substantial low-frequency ripple. An isolated auxiliary circuit based on forward topology is therefore added to the converter to serve as a buffer and a ripple suppression circuit. With TMC, all the power processes can be achieved by a single transformer to lower the size and cost of the converter. In addition, the proposed converter inherits bulk capacitor (auxiliary) voltage clamping capability. The experimental results confirmed the effectiveness of the proposed scheme with high power factor, natural bulk capacitor (auxiliary) clamping voltage, and tight output regulation. DEWEY : 621.38 ISSN : 0278-0046 En ligne : http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5196760 Exemplaires
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Titre : Homogeneous synthesis and characterization of cellulose acetate butyrate (CAB) in 1-Allyl-3-methylimidazolium chloride (AmimCl) ionic liquid Type de document : texte imprimé Auteurs : Yan Cao, Auteur ; Huiquan Li, Auteur ; Jun Zhang, Auteur Année de publication : 2011 Article en page(s) : pp. 7808–7814 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Ionic liquid Résumé : Cellulose acetate butyrate (CAB) with butyryl content of 6–47 wt % was homogeneously synthesized in 1-allyl-3-methylimidazolium chloride (AmimCl) in a single step without using any catalysts. The effects of different acylating agents (acetic anhydride and butyric anhydride) addition methods and reaction conditions on the acyl content of CABs were investigated. Synthesized CABs were characterized by FTIR, NMR, solubility, and thermal analysis. The acylating agents addition method influences the butyryl content, substituent distribution within the anhydroglucose units (AGU), and the properties of CAB. The CAB obtained with butyryl content greater than 38% is completely soluble in 2-methyl–ethyl ketone, 1,2-dichloromethane, ethyl acetate, and butyl acetate. After the mix-acylation, AmimCl can be easily recycled and reused. This study provides a novel way for the clean production of CAB under mild conditions for future industrial applications. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24332103
in Industrial & engineering chemistry research > Vol. 50 N° 13 (Juillet 2011) . - pp. 7808–7814[article] Homogeneous synthesis and characterization of cellulose acetate butyrate (CAB) in 1-Allyl-3-methylimidazolium chloride (AmimCl) ionic liquid [texte imprimé] / Yan Cao, Auteur ; Huiquan Li, Auteur ; Jun Zhang, Auteur . - 2011 . - pp. 7808–7814.
Chimie industrielle
Langues : Anglais (eng)
in Industrial & engineering chemistry research > Vol. 50 N° 13 (Juillet 2011) . - pp. 7808–7814
Mots-clés : Ionic liquid Résumé : Cellulose acetate butyrate (CAB) with butyryl content of 6–47 wt % was homogeneously synthesized in 1-allyl-3-methylimidazolium chloride (AmimCl) in a single step without using any catalysts. The effects of different acylating agents (acetic anhydride and butyric anhydride) addition methods and reaction conditions on the acyl content of CABs were investigated. Synthesized CABs were characterized by FTIR, NMR, solubility, and thermal analysis. The acylating agents addition method influences the butyryl content, substituent distribution within the anhydroglucose units (AGU), and the properties of CAB. The CAB obtained with butyryl content greater than 38% is completely soluble in 2-methyl–ethyl ketone, 1,2-dichloromethane, ethyl acetate, and butyl acetate. After the mix-acylation, AmimCl can be easily recycled and reused. This study provides a novel way for the clean production of CAB under mild conditions for future industrial applications. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24332103 Exemplaires
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