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
Belmiloudi A.,INSA Rennes
Nonlinear Analysis: Real World Applications | Year: 2010
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
INSA Rennes and French National Center for Scientific Research | Date: 2010-05-04
A method and apparatus for multicarrier transmission of a signal representing a source signal. The source signal includes symbols including a set of subcarriers, transmitted simultaneously and having pilot subcarriers intended for at least one processing operation for assisting and/or improving decoding in at least one receiver, and data subcarriers, the location in time-frequency space and a reference value of the pilot subcarriers being known to the at least one receiver. The method of transmission includes: a phase of modifying, for a given symbol, the reference value of at least one subset of the pilot subcarriers, by correction data configured to correct phase and/or amplitude for each of the pilot subcarriers of the subset, so as to minimise peak-to-average power ratio, the correction data taking at least three distinct values, a transition between the values of two successive pilot subcarriers of the subset on a frequency axis being constant.
University of Lorraine, Metz National School of Engineering, Arts, INSA Rennes and French National Center for Scientific Research | Date: 2012-11-07
According to a thermomechanical treatment process for a titanium alloy including between 23 and 27% niobium in atomic proportion, between 0 and 10% zirconium, and between 0 and 1% oxygen, nitrogen and/or silicon, the following steps are performed: a) an increase of a sample of the alloy to a temperature higher than 900 C., b) a fast quench, c) a severe cold strain, d) an ageing treatment at a temperature included between 200 and 600 C., the time of the ageing treatment being included between 10 seconds and 10 minutes. Alloy obtained by this process and prostheses made from such an alloy.