Résultats de l’Enquête internationale 2013 « Quelles activités, quels processus, quelles méthodes, quels systèmes »

International audienc

Management Control, International Observatory 2012

International audienc

Management control – International Observatory 2014

International audienc

Testing data types implementations from algebraic specifications

Algebraic specifications of data types provide a natural basis for testing data types implementations. In this framework, the conformance relation is based on the satisfaction of axioms. This makes it possible to formally state the fundamental concepts of testing: exhaustive test set, testability hypotheses, oracle. Various criteria for selecting finite test sets have been proposed. They depend on the form of the axioms, and on the possibilities of observation of the implementation under test. This last point is related to the well-known oracle problem. As the main interest of algebraic specifications is data type abstraction, testing a concrete implementation raises the issue of the gap between the abstract description and the concrete representation. The observational semantics of algebraic specifications bring solutions on the basis of the so-called observable contexts. After a description of testing methods based on algebraic specifications, the chapter gives a brief presentation of some tools and case studies, and presents some applications to other formal methods involving datatypes

Response of a turbulent boundary layer to a localized unsteady blowing with different temporal forms

A new mechanism by pass in a wall bounded internal flow is proposed and the proposal is checked by direct numerical simulations of high temporal and spatial resolution. The mechanism is based on the interactions of the localized perturbations, rather than the effect of a single perturbation investigated so far in the classical by pass transition process. It is first shown by theoretical considerations that two pairs of quasi-streamwise vortices can interact near the wall in such a manner that the compression (stretching) of the existing wall normal vorticity induced by one of the pairs can enhance a new streamwise vorticity zone that can lead to new coherent structures and enhance considerably the transition process. Direct numerical simulations confirm this hypothesis

Active control effectiveness and synchronization of wall turbulence under localized imposed unsteadinesss

International audienceThe effect of a spatially localized time-periodic perturbation on the efficiency of suboptimal control of the wall turbulence is analyzed. It is shown that the imposed unsteadiness with a frequency in the median production range doubles the turbulent drag reduction under suboptimal control strategy. It is further observed that the spatially averaged turbulent wall shear is synchronized in time with the imposed perturbation waveform. This is related to the synchronization of the unstable periodic orbits present in the near-wall turbulence in connection with the regeneration cycle of turbulence producing coherent structures