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Rennes, France

Ho T.D.,Rennes Institute of Physics | Valance A.,Rennes Institute of Physics | Dupont P.,INSA Rennes | Ould El Moctar A.,CNRS Nantes Thermocinetique Lab
Physical Review Letters | Year: 2011

We report on wind tunnel measurements on saltating particles in a turbulent boundary layer and provide evidence that over an erodible bed the particle velocity in the saltation layer and the saltation length are almost invariant with the wind strength, whereas over a nonerodible bed these quantities vary significantly with the air friction speed. It results that the particle transport rate over an erodible bed does not exhibit a cubic dependence with the air friction speed, as predicted by Bagnold, but a quadratic one. This contrasts with saltation over a nonerodible bed where the cubic Bagnold scaling holds. Our findings emphasize the crucial role of the boundary conditions at the bed and may have important practical consequences for aeolian sand transport in a natural environment. © 2011 American Physical Society. Source

Challamel N.,INSA Rennes
Comptes Rendus - Mecanique | Year: 2011

The post-buckling of an axially loaded elastic beam resting on linearly elastic medium is investigated in this paper from a geometrically exact analysis. It is known that the elastic foundation increases the bifurcation limit, but it may have a destabilizing effect on the post-buckling behavior associated to imperfection sensitivity. This unstable nature of the post-buckling behavior may lead to drastic softening phenomena, as already investigated for plasticity or Continuum Damage Mechanics media. It is suggested in this paper to study the influence of gradient terms in the interaction foundation model on the post-buckling behavior of this structural system. The gradient elasticity foundation model of Pasternak is used and introduced by variational arguments in a geometrically exact framework. A general nonlinear fourth-order differential equation is obtained, and numerically solved with a nonlinear boundary value solver. The post-buckling behavior is analyzed from an asymptotic method. The gradient elasticity constitutive law significantly affects the post-localization process. © 2011 Académie des sciences. Source

This paper considers time-dependent identification problems governed by some generalized transient bioheat transfer type models in biological systems with porous structures and directional blood flow. The analysis and the real applications of the porous media models and biofluid heat transfer in living tissues are relatively recent, however the blood perfusion rate and the porosity parameter affect considerably the effects of thermal physical properties on the transient temperature of biological tissues. The control considered in this work estimates simultaneously these two parameters. The result can be very beneficial for thermal diagnostics in medical practices, for example for laser surgery, photo and thermotherapy for regional hyperthermia, often used in the treatment of cancer. First, the mathematical models are introduced and the existence, the uniqueness and the regularity of the solution of the state equation are proved as well as stability and maximum principle under extra assumptions. Afterwards the identification problems with Tichonov regularization are formulated, in different situations, in order to control the online temperature given by radiometric measurement. An optimal solution is proven to exist and finally necessary optimality conditions are given. Some strategies for numerical realization based on the adjoint variables are provided. © 2009 Elsevier Ltd. All rights reserved. Source

Agency: Cordis | Branch: FP7 | Program: CP | Phase: ICT-2011.1.2 | Award Amount: 9.47M | Year: 2012

Cloud computing is a popular and over-hyped concept in ICT. The concept of infinitely scalable elastic resources changing without complex systems administration and paying only for resources used is attractive. These benefits are not immediately realisable. Within-organisation benefits are realisable at considerable cost. IaaS (Infrastructure as a Service) public CLOUDs have different interfaces and conditions of use thus for an organisation to scale out requires considerable investment using skilled technical staff.\n\nThe business need is to allow organisations to scale out from their private CLOUD to public CLOUDs without a technical chasm between. This cannot easily be achieved. Aligned with the EU strategic direction of an open market for services, SOA (service-oriented architecture) offers a way to virtualise across heterogeneous public CLOUDs and organisational private CLOUDs. It opens a market for European SMEs to provide services to be utilised (and paid for) by business applications and for all organisations to benefit from a catalogue of services that can be used across the environment.\n\nPaaSage will deliver an open and integrated platform, to support both deployment and design of Cloud applications, together with an accompanying methodology that allows model-based development, configuration, optimisation, and deployment of existing and new applications independently of the existing underlying Cloud infrastructures. Specifically it will deliver a CLOUD modelling language, an IDE (Integrated development environment), execution-level mappers and interfaces and a metadata database,\n\nThe Consortium bring together ERCIM for management and STFC as scientific coordinator together with experts in different aspects of CLOUDs ranging from software and services (SINTEF), High Performance Computing (HLRS) and systems development environments (INRIA) to a group of SMEs working on CLOUD systems and end-user organisations with requirements in the CLOUD domain.

Guezouli S.,INSA Rennes | Lachal A.,INSA Rennes
Engineering Structures | Year: 2012

This paper proposes an accurate and efficient 2D nonlinear finite element model to investigate the mechanical behaviour of the shear connection between prefabricated concrete slab and steel girder in composite bridges. Beside material nonlinear constitutive laws and 4-noded plane elements, frictional contact finite elements are introduced in the model at the steel-concrete interface between the girder flange and the concrete slab, between the studs and the embedding concrete and at the base of the concrete slab. Numerical results are compared against experimental results of push-out tests. The tested specimens comprise 4 or 9 studs per slab. Firstly, it is shown that 2D numerical analysis may be accurately used for simulating the original truly 3D problem: a " layer-equivalence" methodology is proposed. A numerical investigation is then carried out to study the influence of the friction coefficient on the load-slip behaviour of the specimen and the distribution of internal deformations and forces in the specimen. A parametric study and some practical recommendations could follow this numerical approach for a better design of the connection. © 2012 Elsevier Ltd. Source

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