Documents disponibles écrits par cet auteur

Characterization and attenuation of sandwiched deadband problem using describing function analysis and application to electrohydraulic systems controlled by closed-center valves / Song Liu in Transactions of the ASME . Journal of dynamic systems, measurement, and control, Vol. 131 N° 3 (Mai 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of dynamic systems, measurement, and control > Vol. 131 N° 3 (Mai 2009) . - 07 p. Titre : Characterization and attenuation of sandwiched deadband problem using describing function analysis and application to electrohydraulic systems controlled by closed-center valves Type de document : texte imprimé Auteurs : Song Liu, Auteur ; Yao Bin, Auteur Année de publication : 2009 Article en page(s) : 07 p. Note générale : dynamic systems Langues : Anglais (eng) Mots-clés : sandwiched  deadband;  dealing;  closed-loop  system Résumé : Unlike input deadband, the sandwiched deadband between actuator and plant dynamics is very difficult to be explicitly compensated for due to the proceeding actuator dynamics whose effect may not be negligible. The paper presents a practical way to overcome the design conservativeness of existing methods in dealing with sandwiched deadband. Specifically, a describing function based nonlinear analysis method is proposed to characterize the effect of the sandwiched deadband on the stability and performance of the overall closed-loop system. The analysis results can be used to determine the highest closed-loop bandwidth that can be achieved without inducing residual limit cycles and instability. Optimal controller parameters can then be found to maximize the achievable closed-loop control performance. The technique is applied to an electrohydraulic system controlled by closed-center valves and a nonlinear feedback controller. Simulation results showed severe oscillations as the feedback control gains are increased to the predicted threshold values. Comparative experimental results also showed the effectiveness of the proposed method in reducing the conservativeness of traditional design and the improved closed-loop control performance in implementation. DEWEY : 629.8 ISSN : 0022-0434 En ligne : http://dynamicsystems.asmedigitalcollection.asme.org/issue.aspx?journalid=117&is [...] [article] Characterization and attenuation of sandwiched deadband problem using describing function analysis and application to electrohydraulic systems controlled by closed-center valves [texte imprimé] / Song Liu, Auteur ; Yao Bin, Auteur . - 2009 . - 07 p. dynamic systems Langues : Anglais (eng) in Transactions of the ASME . Journal of dynamic systems, measurement, and control > Vol. 131 N° 3 (Mai 2009) . - 07 p. Mots-clés : sandwiched  deadband;  dealing;  closed-loop  system Résumé : Unlike input deadband, the sandwiched deadband between actuator and plant dynamics is very difficult to be explicitly compensated for due to the proceeding actuator dynamics whose effect may not be negligible. The paper presents a practical way to overcome the design conservativeness of existing methods in dealing with sandwiched deadband. Specifically, a describing function based nonlinear analysis method is proposed to characterize the effect of the sandwiched deadband on the stability and performance of the overall closed-loop system. The analysis results can be used to determine the highest closed-loop bandwidth that can be achieved without inducing residual limit cycles and instability. Optimal controller parameters can then be found to maximize the achievable closed-loop control performance. The technique is applied to an electrohydraulic system controlled by closed-center valves and a nonlinear feedback controller. Simulation results showed severe oscillations as the feedback control gains are increased to the predicted threshold values. Comparative experimental results also showed the effectiveness of the proposed method in reducing the conservativeness of traditional design and the improved closed-loop control performance in implementation. DEWEY : 629.8 ISSN : 0022-0434 En ligne : http://dynamicsystems.asmedigitalcollection.asme.org/issue.aspx?journalid=117&is [...]

New refreshable n-halamine polymeric biocides: n-chlorination of acyclic amide grafted cellulose / Song Liu in Industrial & engineering chemistry research, Vol. 48 N°2 (Janvier 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N°2 (Janvier 2009) . - p. 613–618 Titre : New refreshable n-halamine polymeric biocides: n-chlorination of acyclic amide grafted cellulose Type de document : texte imprimé Auteurs : Song Liu, Auteur ; Gang Sun, Auteur Année de publication : 2009 Article en page(s) : p. 613–618 Note générale : chemical engineering Langues : Anglais (eng) Mots-clés : antibacterial--  functions  polymerization--processes Résumé : Acyclic N-halamine structures have demonstrated antibacterial functions similar to cyclic N-halamine. Precursors of acyclic halamine such as acrylamide and methacrylamide can be easily grafted onto surfaces of substrates via radical polymerization processes. However, due to easy hydrolysis of primary amides during chlorination and steric hindrance of secondary amide to conversion to acyclic halamine structures, the acyclic halamines still have limitations to many applications in preparation of antimicrobial materials. To reduce hydrolysis of amide during chlorination, particularly under alkaline conditions, addition of electrolytes such as NaCl was able to improve chlorination of polyacrylamide grafted cotton (chlorine content 458 ppm) with less than 10% hydrolysis under slightly basic (pH = 8) conditions. Both acidic conditions and the addition of salt can increase the chlorination of secondary amides and provide effective antibacterial functions on the treated cellulose (5 log reduction of E. coli in contact time of 120 min). En ligne : http://pubs.acs.org/doi/abs/10.1021/ie8007902 [article] New refreshable n-halamine polymeric biocides: n-chlorination of acyclic amide grafted cellulose [texte imprimé] / Song Liu, Auteur ; Gang Sun, Auteur . - 2009 . - p. 613–618. chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N°2 (Janvier 2009) . - p. 613–618 Mots-clés : antibacterial--  functions  polymerization--processes Résumé : Acyclic N-halamine structures have demonstrated antibacterial functions similar to cyclic N-halamine. Precursors of acyclic halamine such as acrylamide and methacrylamide can be easily grafted onto surfaces of substrates via radical polymerization processes. However, due to easy hydrolysis of primary amides during chlorination and steric hindrance of secondary amide to conversion to acyclic halamine structures, the acyclic halamines still have limitations to many applications in preparation of antimicrobial materials. To reduce hydrolysis of amide during chlorination, particularly under alkaline conditions, addition of electrolytes such as NaCl was able to improve chlorination of polyacrylamide grafted cotton (chlorine content 458 ppm) with less than 10% hydrolysis under slightly basic (pH = 8) conditions. Both acidic conditions and the addition of salt can increase the chlorination of secondary amides and provide effective antibacterial functions on the treated cellulose (5 log reduction of E. coli in contact time of 120 min). En ligne : http://pubs.acs.org/doi/abs/10.1021/ie8007902