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Augier F.,French Institute of Petroleum | Idoux F.,French Institute of Petroleum | Delenne J.Y.,CNRS Mechanical and Civil Engineering Laboratory
Chemical Engineering Science | Year: 2010

In this study, we investigate the transport and transfer properties inside packed beds of spherical particles by means of CFD simulations. Heat and mass transfer properties have been computed in packing configurations of increasing complexity at low to moderate Reynolds numbers (1

Malachanne E.,Ecole des Mines d'Ales | Dureisseix D.,CNRS Contacts and Structural Mechanics Laboratory | Jourdan F.,CNRS Mechanical and Civil Engineering Laboratory
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2011

In this article, a phenomenological numerical model of bone remodeling is proposed. This model is based on the poroelasticity theory in order to take into account the effects of fluid movements in bone adaptation. Moreover, the proposed remodeling law is based on the classical 'Stanford' law, enriched in order to take into account the loading frequency, through fluid movements. This coupling is materialized by a quadratic function of Darcy velocity. The numerical model is carried out, using a finite element method, and calibrated using experimental results at macroscopic level, from the literature. First results concern cyclic loadings on a mouse ulna, at different frequencies between 1Hz and 30Hz, for a force amplitude of 1.5N and 2N. Experimental results exhibit a sensitivity to the loading frequency, with privileged frequency for bone remodeling between 5Hz and 10Hz, for the force amplitude of 2N. For the force amplitude of 1.5N, no privileged frequencies for bone remodeling are highlighted. This tendency is reproduced by the proposed numerical computations. The model is identified on a single case (one frequency and one force amplitude) and validated on the other ones. The second experimental validation deals with a different loading regime, an internal fluid pressure at 20Hz on a turkey ulna. The same framework is applied, and the numerical and experimental data are still matching in terms of gain in bone mass density. © 2011 Elsevier Ltd.

Dresp-Langley B.,CNRS Mechanical and Civil Engineering Laboratory | Reeves A.,Northeastern University
Seeing and Perceiving | Year: 2012

We show that true colors as defined by Chevreul (1839) produce unsuspected simultaneous brightness induction effects on their immediate grey backgrounds when these are placed on a darker (black) general background surrounding two spatially separated configurations. Assimilation and apparent contrast may occur in one and the same stimulus display. We examined the possible link between these effects and the perceived depth of the color patterns which induce them as a function of their luminance contrast. Patterns of square-shaped inducers of a single color (red, green, blue, yellow, or grey) were placed on background fields of a lighter and a darker grey, presented on a darker screen. Inducers were always darker on one side of the display and brighter on the other in a given trial. The intensity of the grey backgrounds varied between trials only. This permitted generating four inducer luminance contrasts, presented in random order, for each color. Background fields were either spatially separated or consisted of a single grey field on the black screen. Experiments were run under three environmental conditions: dark-adaptation, daylight, and rod-saturation after exposure to bright light. In a first task, we measured probabilities of contrast, assimilation, and no effect in a three-alternative forced-choice procedure (background appears brighter on the 'left', on the 'right' or the 'same'). Visual adaptation and inducer contrast had no significant influence on the induction effects produced by colored inducers. Achromatic inducers produced significantly stronger contrast effects after dark-adaptation, and significantly stronger assimilation in daylight conditions. Grouping two backgrounds into a single one was found to significantly decrease probabilities of apparent contrast. Under the same conditions, we measured probabilities of the inducers to be perceived as nearer to the observer (inducers appear nearer on 'left', on 'right' or the 'same'). These, as predicted by Chevreul's law of contrast, were determined by the luminance contrast of the inducers only, with significantly higher probabilities of brighter inducers to be seen as nearer, and a marked asymmetry between effects produced by inducers of opposite sign. Implications of these findings for theories which attempt to link simultaneous induction effects to the relative depth of object surfaces in the visual field are discussed. © 2012 Koninklijke Brill NV, Leiden.

Gioia F.,Marche Polytechnic University | Dureisseix D.,CNRS Contacts and Structural Mechanics Laboratory | Motro R.,CNRS Mechanical and Civil Engineering Laboratory | Maurin B.,CNRS Mechanical and Civil Engineering Laboratory
Journal of Mechanical Design, Transactions of the ASME | Year: 2012

Origami and paperfolding techniques may inspire the design of structures that have the ability to be folded and unfolded: their geometry can be changed from an extended, servicing state to a compact one, and back-forth. In traditional origami, folds are introduced in a sheet of paper (a developable surface) for transforming its shape, with artistic, or decorative intent; in recent times the ideas behind origami techniques were transferred in various design disciplines to build developable foldable/unfoldable structures, mostly in aerospace industry (Miura, 1985, "Method of Packaging and Deployment of Large Membranes in Space," Inst. Space Astronaut. Sci. Rep., 618, pp. 1-9; Ikema, 2009, "Deformation Analysis of a Joint Structure Designed for Space Suit With the Aid of an Origami Technology," 27th International Symposium on Space Technology and Science (ISTS)). The geometrical arrangement of folds allows a folding mechanism of great efficiency and is often derived from the buckling patterns of simple geometries, like a plane or a cylinder (e.g., Miura-ori and Yoshimura folding pattern) (Wu et al., 2007, "Optimization of Crush Characteristics of the Cylindrical Origami Structure," Int. J. Veh. Des., 43, pp. 66-81; Hunt and Ario, 2005, "Twist Buckling and the Foldable Cylinder: An Exercise in Origami," Int. J. Non-Linear Mech., 40(6), pp. 833-843). Here, we interest ourselves to the conception of foldable/unfoldable structures for civil engineering and architecture. In those disciplines, the need for folding efficiency comes along with the need for structural efficiency (stiffness); for this purpose, we will explore nondevelopable foldable/unfoldable structures: those structures exhibit potential stiffness because, when unfolded, they cannot be flattened to a plane (nondevelopability). In this paper, we propose a classification for foldable/unfoldable surfaces that comprehend non fully developable (and also non fully foldable) surfaces and a method for the description of folding motion. Then, we propose innovative geometrical configurations for those structures by generalizing the Miura-ori folding pattern to nondevelopable surfaces that, once unfolded, exhibit curvature. © 2012 American Society of Mechanical Engineers.

Jullien D.,CNRS Mechanical and Civil Engineering Laboratory | Widmann R.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Loup C.,CNRS Mechanical and Civil Engineering Laboratory | Thibaut B.,CNRS Mechanical and Civil Engineering Laboratory
Annals of Forest Science | Year: 2013

Aims: In European Beech (Fagus sylvatica L.) large growth stresses lead to severe log end splitting that devaluate beech timber. Our study aimed at detecting relationships between growth stress and some morphology parameters in trees. Methods: Growth stress indicators were recorded for 440 mature trees in nine stands from five European countries, together with morphology parameters. Results: Most trees displayed an uneven distribution of growth stress around the trunk. Moreover, growth stress intensity varied largely between individual trees. Geometry of the trunk was a poor predictor of growth stress intensity. Crown asymmetry resulted in a larger stress dissymmetry within trees. Trunk inclination was not correlated to max tension stress, contrary to what is usually found in younger trees. In the case of small inclination, growth stress was close to expected from biomechanics of restoring verticality. Trees exhibiting a larger inclination probably evolved a different mechanical solution: a rather large crown, lower tree slenderness and a sufficient asymmetry in growth stress as to prevent a higher inclination due to growth. Conclusion: A large slenderness is the best accurate predictor of a large growth stress, although variations in the ratio height/diameter at breast height explained only 10 % of the variability of growth stress. A large crown surface was the best predictor of a low level of growth stress. A large spacing between trees seems a good solution to lower the risk of growth stress in mature beech. © 2012 INRA and Springer-Verlag France.

Boutin C.,National School of Public Civil Engineering | Royer P.,CNRS Mechanical and Civil Engineering Laboratory
Geophysical Journal International | Year: 2015

This paper focuses on the modelling of fluid-filled poroelastic double porosity media under quasi-static and dynamic regimes. The double porosity model is derived from a two-scale homogenization procedure, by considering a medium locally characterized by blocks of poroelastic Biot microporous matrix and a surrounding system of fluid-filledmacropores or fractures. The derived double porosity description is a two-pressure field poroelastic model with memory and viscoelastic effects. These effects result from the 'time-dependent' interaction between the pressure fields in the two pore networks. It is shown that this homogenized double porosity behaviour arises when the characteristic time of consolidation in the microporous domain is of the same order of magnitude as the macroscopic characteristic time of transient regime. Conversely, single porosity behaviours occur when both timescales are clearly distinct. Moreover, it is established that the phenomenological approaches that postulate the coexistence of two pressure fields in 'instantaneous' interaction only describe media with two pore networks separated by an interface flow barrier. Hence, they fail at predicting and reproducing the behaviour of usual double porosity media. Finally, the results are illustrated for the case of stratified media. © The Authors 2015.

Mutabaruka P.,CNRS Mechanical and Civil Engineering Laboratory | Delenne J.-Y.,Montpellier University | Soga K.,University of Cambridge | Radjai F.,Montpellier University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2014

By means of coupled molecular dynamics-computational fluid dynamics simulations, we analyze the initiation of avalanches in a granular bed of spherical particles immersed in a viscous fluid and inclined above its angle of repose. In quantitative agreement with experiments, we find that the bed is unstable for a packing fraction below 0.59 but is stabilized above this packing fraction by negative excess pore pressure induced by the effect of dilatancy. From detailed numerical data, we explore the time evolution of shear strain, packing fraction, excess pore pressures, and granular microstructure in this creeplike pressure redistribution regime, and we show that they scale excellently with a characteristic time extracted from a model based on the balance of granular stresses in the presence of a negative excess pressure and its interplay with dilatancy. The cumulative shear strain at failure is found to be ≃0.2, in close agreement with the experiments, irrespective of the initial packing fraction and inclination angle. Remarkably, the avalanche is triggered when dilatancy vanishes instantly as a result of fluctuations while the average dilatancy is still positive (expanding bed) with a packing fraction that declines with the initial packing fraction. Another nontrivial feature of this creeplike regime is that, in contrast to dry granular materials, the internal friction angle of the bed at failure is independent of dilatancy but depends on the inclination angle, leading therefore to a nonlinear dependence of the excess pore pressure on the inclination angle. We show that this behavior may be described in terms of the contact network anisotropy, which increases with a nearly constant connectivity and levels off at a value (critical state) that increases with the inclination angle. These features suggest that the behavior of immersed granular materials is controlled not only directly by hydrodynamic forces acting on the particles but also by the influence of the fluid on the granular microstructure. © 2014 American Physical Society.

Bellieud M.,CNRS Mechanical and Civil Engineering Laboratory
Archive for Rational Mechanics and Analysis | Year: 2012

We study a notion of capacity related to elasticity which proves convenient for analyzing the concentrations of strain energy caused by rigid displacements of some infinitesimal parts of an elastic body in two or three dimensions. By way of application, we investigate the behavior of solutions to initial boundary value problems describing vibrations of periodic elastic composites with rapidly varying elastic properties. More specifically, we analyze a two-phase medium whereby a set of heavy stiff tiny particles is embedded in a softer matrix. This task is set in the context of linearized elasticity. © 2011 Springer-Verlag.

Weller T.,CNRS Mechanical and Civil Engineering Laboratory | Licht C.,CNRS Mechanical and Civil Engineering Laboratory
Comptes Rendus - Mecanique | Year: 2012

We extend our modeling of smart structures to the second order piezoelectricity. We show that three different models have to be taken into account, which broadens the scope of the sensors and actuators field. The second order piezoelectricity being compatible with isotropy, we also propose a systematic study of the impact of crystalline symmetries on our models. © 2012 Académie des sciences.

Anza Hafsa O.,CNRS Mechanical and Civil Engineering Laboratory
ESAIM - Control, Optimisation and Calculus of Variations | Year: 2010

We study the integral representation of relaxed functionals in the multi-dimensional calculus of variations, for integrands which are finite in a convex bounded set with nonempty interior and infinite elsewhere. © 2008 EDP Sciences, SMAI.

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