Theory of low frequency noise transmission through turbines

Improvements of the existing theory of low frequency noise transmission through turbines and development of a working prediction tool are described. The existing actuator-disk model and a new finite-chord model were utilized in an analytical study. The interactive effect of adjacent blade rows, higher order spinning modes, blade-passage shocks, and duct area variations were considered separately. The improved theory was validated using the data acquired in an earlier NASA program. Computer programs incorporating the improved theory were produced for transmission loss prediction purposes. The programs were exercised parametrically and charts constructed to define approximately the low frequency noise transfer through turbines. The loss through the exhaust nozzle and flow(s) was also considered

Attenuation of upstream-generated low frequency noise by gas turbines

The acoustic transfer functions of low frequency (below 3500 Hz) noise through aircraft turbines were investigated. Model test results were compared with theoretical predictions in order to assess the validity of the theory. Component tests were conducted on both high pressure and low pressure model turbines. The influence of inlet temperature and turbine speed attenuation was evaluated, while the effects of turbine pressure ratio, blade-row choking, and additional downstream stages were determined. Preliminary identification of pertinent aeroacoustic correlating parameters was made

Analytical evaluation of the output variability in production systems with general Markovian structure

Performance evaluation models are used by companies to design, adapt, manage and control their production systems. In the literature, most of the effort has been dedicated to the development of efficient methodologies to estimate the first moment performance measures of production systems, such as the expected production rate, the buffer levels and the mean completion time. However, there is industrial evidence that the variability of the production output may drastically impact on the capability of managing the system operations, causing the observed system performance to be highly different from what expected. This paper presents a general methodology to analyze the variability of the output of unreliable single machines and small-scale multi-stage production systems modeled as General Markovian structure. The generality of the approach allows modeling and studying performance measures such as the variance of the cumulated output and the variance of the inter-departure time under many system configurations within a unique framework. The proposed method is based on the characterization of the autocorrelation structure of the system output. The impact of different system parameters on the output variability is investigated and characterized. Moreover, managerial actions that allow reducing the output variability are identified. The computational complexity of the method is studied on an extensive set of computer experiments. Finally, the limits of this approach while studying long multi-stage production lines are highlighted. © 2013 Springer-Verlag Berlin Heidelberg

"Manger tradition" ou la fabrication d'un patrimoine alimentaire inégal (Lima, Pérou)

La patrimonialisation accompagne en Amérique Latine un vaste mouvement de globalisation des ressources locales, naturelles comme culturelles. Politique publique, elle est également un vecteur de développement local. Fortement médiatisés, les patrimoines alimentaires matériels et immatériels explicitent divers clivages sociaux et culturels, politiques, économiques et territoriaux, et se présentent comme des constructions standardisées et hétérogènes, singulières et locales. Leur valorisation et mises en scène conduisent à s'interroger sur les modalités de leur production, au-delà des questions de sauvegarde et d'inventaire. À partir de trois exemples péruviens (Lima), nous montrerons comment les mises à distances et les rapprochements, opérés par rapport à un espace-temps alimentaire "idéel", participent à la construction d'un patrimoine inégal. De quelle façon les chefs et restaurateurs convoquent la "tradition" et le "traditionnel" ? Les contours larges de ces termes n'occultent-ils pas des relations sociales inégalitaires ? Cet article appelle à reconsidérer l'opposition tenue pour acquise entre patrimoines institués (reconnus par les ministères de la culture ou l'Unesco) d'un côté et constructions patrimoniales locales de l'autre, compte tenu de l'importance grandissante que prennent les dimensions immatérielles de l'alimentation

Effect of Temperature & Concentration on Dissolution Potentials of Sodium Chloride, Bromide & Iodide

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