Efficacité

Résumé

L'efficacité est la capacité, d'une personne, d'un groupe ou d'un système, à parvenir à ses fins, à ses objectifs (ou à ceux qu'on lui a fixés). Être efficace revient à produire à l'échéance prévue les résultats escomptés et réaliser des objectifs fixés, objectifs qui peuvent être définis en termes de quantité, mais aussi de qualité, de rapidité, de coûts, de rentabilité, etc. La notion d'efficacité est largement utilisée dans les activités économiques et de gestion, mais pas seulement : elle est employée dans les domaines scientifiques : chimie, catalyse, biochimie, biologie, mécanique, thermodynamique, etc. L'efficacité est une notion large qui comprend d'autres termes voisins, avec lesquels elle ne saurait être confondue :

l'efficience qui est la capacité à atteindre des objectifs au prix d'une consommation minimale de ressources (personnel, matériel, finances). Il s'agit de réaliser les objectifs de l'organisation (ou une partie de celle-ci) avec le minimum de coûts.
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Source officielle

https://fr.wikipedia.org/wiki/Efficacit%C3%A9

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Effectively managing a large collection of multimedia documents is a challenge, addressed by many disciplines from signal processing through database systems to artificial intelligence and interaction design. The problems to be solved have rarely been considered together. We propose a series of novel solutions for: the system architecture, the document content characterization, the retrieval methodology, and the user interaction schemes. We propose and describe a communicating components architecture using a new open and flexible protocol for messaging. Its foundation, the multimedia retrieval markup language (mrml) is specified with examples of the benefits of this approach. The general multimedia application domain is restricted mainly to image documents that carry semantic annotation like captions or meta-data. The integration of perceptual and semantic content descriptions into a single retrieval structure is the principal contribution of our work. The proposed method allows for improved effectiveness, augmented functionality and high flexibility for the extension to other media types like audio or video. The relationships among the two different representational characteristics can be exploited for more effective retrieval and other tasks like semi-automatic image annotation or illustration of semantic concepts. The final contribution is the study and implementation of user interaction metaphors that are intuitive and attempt to further bridge the gap between user's and system's notion of relevance. A rich set of information need formulation tools is proposed to users of varying skill and of varying requirements. Merging query specification with result visualization and browsing, using interactively explorable search spaces, offers a single access point to most retrieval tasks.

EPFL2003

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Highly-loaded impellers, typically used in turbocharger and gas turbine applications, exhaust an unsteady, transonic flow that is non-uniform across the span and pitch and swirling at angles approaching tangential. With the exception of the flow angle, conflicting data exist regarding whether these attributes have substantial influence on the performance of the downstream diffuser. This paper quantifies the relative importance of the flow angle, Mach number, non-uniformity and unsteadiness on diffuser performance, through diffuser experiments in a compressor stage and in a rotating swirling flow test rig. This is combined with steady and unsteady Reynolds-Averaged Navier Stokes computations. The test article is a pressure ratio 5 turbocharger compressor with an airfoil vaned diffuser. The swirling flow rig is able to generate rotor outflow conditions representative of the compressor except for the periodic pitchwise unsteadiness, and fits a 0.86 scale diffuser and volute. In both rigs, the time-mean impeller outflow is mapped across a diffuser pitch using miniaturized traversing probes developed for the purpose. Across approximately two-thirds of the stage operating range, diffuser performance is well correlated to the average impeller outflow angle when the metric used is effectiveness, which describes the pressure recovery obtained relative to the maximum possible given the average inflow angle, Mach number and the vane exit metal angle. Utilizing effectiveness captures density changes through the diffuser at higher Mach numbers; a 10% increase in pressure recovery is observed as the inlet Mach number is increased from 0.5 to 1. Further, effectiveness is shown to be largely independent of the time-averaged spanwise and unsteady pitchwise non-uniformity from the rotor; this independence is reflective of the strong mixing processes that occur in the diffuser inlet region. The observed exception is for operating points with high time-averaged vane incidence. Here, it is hypothesized that temporary excursions into high-loss flow regimes cause a non-linear increase in loss as large unsteady angle variations pass by from the rotor. Given that straight-channel diffuser design charts typically used in preliminary radial vaned diffuser design capture neither streamtube area changes from impeller exit to the diffuser throat nor vane incidence effects, their utility is limited. An alternative approach, utilizing effectiveness and vane leading edge incidence, is proposed.

Amer Soc Mechanical Engineers2016

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Highly loaded impellers, typically used in turbocharger and gas turbine applications, exhaust an unsteady, transonic flow that is nonuniform across the span and pitch and swirling at angles approaching tangential. With the exception of the flow angle, conflicting data exist regarding whether these attributes have substantial influence on the performance of the downstream diffuser. This paper quantifies the relative importance of the flow angle, Mach number, nonuniformity, and unsteadiness on diffuser performance, through diffuser experiments in a compressor stage and in a rotating swirling flow test rig. This is combined with steady and unsteady Reynolds-averaged Navier–Stokes (RANS) computations. The test article is a pressure ratio 5 turbocharger compressor with an airfoil vaned diffuser. The swirling flow rig is able to generate rotor outflow conditions representative of the compressor except for the periodic pitchwise unsteadiness and fits a 0.86 scale diffuser and volute. In both rigs, the time-mean impeller outflow is mapped across a diffuser pitch using miniaturized traversing probes developed for the purpose. Across approximately two-thirds of the stage operating range, diffuser performance is well correlated to the average impeller outflow angle when the metric used is effectiveness, which describes the pressure recovery obtained relative to the maximum possible given the average inflow angle and Mach number and the vane exit metal angle. Utilizing effectiveness captures density changes through the diffuser at higher Mach numbers; a 10% increase in pressure recovery is observed as the inlet Mach number is increased from 0.5 to 1. Further, effectiveness is shown to be largely independent of the time-averaged spanwise and unsteady pitchwise nonuniformity from the rotor; this independence is reflective of the strong mixing processes that occur in the diffuser inlet region. The observed exception is for operating points with high time-averaged vane incidence. Here, it is hypothesized that temporary excursions into high-loss flow regimes cause a nonlinear increase in loss as large unsteady angle variations pass by from the rotor. Given that straight-channel diffuser design charts typically used in preliminary radial vaned diffuser design capture neither streamtube area changes from impeller exit to the diffuser throat nor vane incidence effects, their utility is limited. An alternative approach, utilizing effectiveness and vane leading edge incidence, is proposed.

American Society of Mechanical Engineers2017

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Amer Soc Mechanical Engineers2016

American Society of Mechanical Engineers2017