Longere P.,Higher Institute of Aeronautics and Space |
Dragon A.,National Engineering School of Mechanical and Aeronautical Engineering
Mechanics of Materials
Ductile fracture of metals by void nucleation, growth and coalescence under positive stress triaxiality is well admitted. This is not the case when metals are submitted to negative stress triaxiality. The present work aims at contributing to a better understanding of the competition between micro-mechanisms at the origin of failure of metals when submitted to shear-pressure loading at low and high strain rates. With this aim in view, experiments were carried out on Ti-6Al-4V shear-compression samples involving a stress triaxiality range comprised between -0.2 and -0.5. Results show that the material failure is the consequence of a void growth induced process. At high strain rate, due to the localization of the deformation within adiabatic shear bands, the failure of the material occurs earlier, leading to maximum shear strain smaller at high strain rate than at low strain rate. Impact tests were also carried out on Kalthoff and Winkler type double notched plates. They showed that the interaction between tension and shear waves leads to a complex Mode I-Mode II crack propagation. © 2014 Elsevier Ltd. All rights reserved. Source
Jardin T.,Higher Institute of Aeronautics and Space |
David L.,University of Poitiers
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics
At high angles of attack, an aircraft wing stalls. This dreaded event is characterized by the development of a leading edge vortex on the upper surface of the wing, followed by its shedding which causes a drastic drop in the aerodynamic lift. At similar angles of attack, the leading edge vortex on an insect wing or an autorotating seed membrane remains robustly attached, ensuring high sustained lift. What are the mechanisms responsible for both leading edge vortex attachment and high lift generation on revolving wings? We review the three main hypotheses that attempt to explain this specificity and, using direct numerical simulations of the Navier-Stokes equations, we show that the latter originates in Coriolis effects. © 2015 American Physical Society. Source
Agency: Cordis | Branch: H2020 | Program: RIA | Phase: FETOPEN-RIA-2014-2015 | Award Amount: 3.42M | Year: 2015
Wireless Chip-to-Chip (C2C) communication and wireless links between printed circuit boards operating as Multiple Input Multiple Output devices need to become dominant features of future generations of integrated circuits and chip architectures. They will be able to overcome the information bottleneck due to wired connections and will lead the semiconductor industry into a new More-Than-Moore era. Designing the architecture of these wireless C2C networks is, however, impossible today based on standard engineering design tools. Efficient modelling strategies for describing noisy electromagnetic fields in complex environments are necessary for developing these new chip architectures and wireless interconnectors. Device modelling and chip optimization procedures need to be based on the underlying physics for determining the electromagnetic fields, the noise models and complex interference pattern. In addition, they need to take into account input signals of modern communication systems being modulated, coded, noisy and eventually disturbed by other signals and thus extremely complex. Recent advances both in electrical engineering and mathematical physics make it possible to deliver the breakthroughs necessary to enable this future emerging wireless C2C technology by creating a revolutionary electromagnetic field simulation toolbox. Increasingly sophisticated physical models of wireless interconnects and associated signal processing strategies and new insight into wave modelling in complex environments based on dynamical systems theory and random matrix theory make it possible to envisage wireless communication on a chip level. This opens up completely new pathways for chip design, for carrier frequency ranges as well as for energy efficiency and miniaturisation, which will shape the electronic consumer market in the 21st century.
Agency: Cordis | Branch: H2020 | Program: RIA | Phase: MG-1.5-2014 | Award Amount: 3.14M | Year: 2015
With the ULTIMATE project five experienced research groups and four major European engine manufacturers will develop innovative propulsion systems to fulfill the SRIA 2050 key challenges. One of the most challenging targets is the 75% reduction in energy consumption and CO2-emissions. Technologies currently at TRL 3-5, cannot achieve this aim. It is estimated that around a 30% reduction must come from radical innovations now being at lower TRL. Thus, European industry needs synergetic breakthrough technologies for every part of the air transport system, including the airframe, propulsion and power. The ULTIMATE project singles out the major loss sources in a state of the art turbofan (combustor irreversibility, core exhaust heat, bypass exhaust kinetic energy). These are then used to categorize breakthrough technologies (e.g. piston topping, intercooling & exhaust heat exchangers, and advanced propulsor & integration concepts). This classification approach gives a structured way to combine and explore synergies between the technologies in the search for ultralow CO2, NOx and noise emissions. The most promising combinations of radical technologies will then be developed for a short range European and a long range intercontinental advanced tube and wing aircraft. Through the EU projects VITAL, NEWAC, DREAM, LEMCOTEC, E-BREAK and ENOVAL, the ULTIMATE partners have gained the most comprehensive experience in Europe on conception and evaluation of advanced aero engine architectures. Existing tools, knowledge and models will be used to perform optimization and evaluation against the SRIA targets to mature the technologies to TRL 2. Road maps will be set up to outline the steps to develop the technologies into products and bring them onto the market. These road maps will also provide a way forward for future European propulsion and aviation research.
Masmoudi M.,Jean Monnet University |
Hait A.,Higher Institute of Aeronautics and Space
Engineering Applications of Artificial Intelligence
In the real world, projects are subject to numerous uncertainties at different levels of planning. Fuzzy project scheduling is one of the approaches that deal with uncertainties in project scheduling problem. In this paper, we provide a new technique that keeps uncertainty at all steps of the modelling and solving procedure by considering a fuzzy modelling of the workload inspired from the fuzzy/possibilistic approach. Based on this modelling, two project scheduling techniques, Resource Constrained Scheduling and Resource Leveling, are considered and generalized to handle fuzzy parameters. We refer to these problems as the Fuzzy Resource Constrained Project Scheduling Problem (FRCPSP) and the Fuzzy Resource Leveling Problem (FRLP). A Greedy Algorithm and a Genetic Algorithm are provided to solve FRCPSP and FRLP respectively, and are applied to civil helicopter maintenance within the framework of a French industrial project called Helimaintenance. © 2012 Elsevier Ltd. All rights reserved. Source