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Vandœuvre-lès-Nancy, France

Ganghoffer J.-F.,LEMTA ENSEM
Lecture Notes in Applied and Computational Mechanics | Year: 2010

The connections between the notion of Eshelby tensor and the variation of Hamiltonian like action integrals are investigated, in connection with the thermodynamics of continuous open bodies exchanging mass, heat and work with their surrounding. Considering first a homogeneous representative volume element (RVE), it is shown that a possible choice of the Lagrangian density is the material derivative of a suitable thermodynamic potential. The Euler equations of the so built action integral are the state laws written in rate form. As the consequence of the optimality conditions of the resulting Jacobi action, the vanishing of the surface contribution resulting from the general variation of this Hamiltonian action leads to the well-known Gibbs-Duhem condition. A general three-field variational principle describing the equilibrium of heterogeneous systems is next written, based on the zero potential, the stationnarity of which delivers a balance law for a generalized Eshelby tensor in a thermodynamic context. Adopting the rate of the grand potential as the lagrangian density, a generalized Gibbs-Duhem condition is obtained as the transversality condition of the thermodynamic action integral, considering a solid body with a movable boundary. © 2010 Springer-Verlag Berlin Heidelberg.

Rachedi M.,University of Science and Technology Houari Boumediene | Feidt M.,LEMTA ENSEM | Amirat M.,University of Science and Technology Houari Boumediene | Merzouk M.,Blida University
Applied Thermal Engineering | Year: 2016

In the context of thermodynamic analysis of finite dimensions systems, we studied the optimum operating conditions of an endoreversible thermal machine. In this study, we considered a transcritical cycle, considering external irreversibilities. The hot reservoir is a low enthalpy geothermal heat source; therefore, it is assumed to be finite, whereas the cold reservoir is assumed to be infinite. The power optimisation is investigated by searching the optimum effectiveness of the heat-exchanger at the hot side of the engine. The sum of the total effectiveness and the second law of thermodynamics are used as constraints for optimisation. The optimal temperatures of the working fluid and optimum performances are evaluated based on the most significant parameters of the system: (1) the ratio of heat capacity rate of the working fluid to the heat capacity rate of the coolant and (2) the ratio of the sink temperature to the temperature of the hot source. The parametric study of the cycle and its approximation by a trilateral cycle enabled us to determine the optimum value of the effectiveness of the heat exchangers and the optimal operating temperatures of the cycle considered. The efficiencies obtained are in the range of 15–25% and was found to exceed the efficiency expected by the Curzon and Ahlborn prevision; meanwhile, the Carnot efficiency remains at a high limit. © 2016 Elsevier Ltd

Ganghoffer J.-F.,LEMTA ENSEM | Kabouya N.,University of Ghardaia | Mefti N.,Enitec
Journal of Biomechanics | Year: 2010

Models of the adhesion of a population of cells in a plane flow are developed, considering the dilute regime. Cells considered as rigid punctual entities are virtually injected at regular times within a plane channel limited by two fixed planes. The pressure profile is supposed to be triangular (constant gradient), in accordance with the assumptions of a Poiseuille flow. The cell adherence to the channel wall is governed by the balance of forces, accounting for gravity, non-specific physical interactions, such as electrostatic effects (repulsive) and Van der Waals forces (attractive), specific adhesive forces representing the ligand-receptor interactions, and friction between cells and the fluid in the vicinity of the endothelium wall. The spatial distribution of the adhesion molecules along the wall is supposed to be a random event, accounted for by a stochastic spatial variability of the dipolar moments of those molecules, according to a Gaussian process. Experimental trends reported for the rate of aggregation of L-selectin mediated leukocytes under shear flow are in qualitative accordance with the evolution versus time of adhering cells obtained by the present simulations. The effect of the maximal injection pressure on those kinetics is assessed. © 2009 Elsevier Ltd. All rights reserved.

Ganghoffer J.-F.,LEMTA ENSEM | Magnenet V.,British Petroleum | Rahouadj R.,LEMTA ENSEM
Journal of Engineering Mathematics | Year: 2010

The interest and relevance of symmetry methods as a predictive and systematic methodology in the continuum mechanics of materials is analyzed, relying on a classification of the inherent aspects in terms of the direct, extended direct, and inverse methods. Although being interrelated, these three problems each have a specific argumentation which is separately exposed in the present contribution. The direct problem of finding invariants associated with a given constitutive law for materials, including dissipation, is first envisaged. The abstract formulation of constitutive laws in terms of the state laws and a dissipation potential expressing the evolution of internal state variables is considered, in the framework of irreversible thermodynamics. It is shown that a specific choice of the components of the symmetry vector acting in the space of independent and dependent variables leads to a local invariance condition of the constitutive law fully equivalent to the variational symmetry condition using the rate of the internal energy density. As a specific situation involving this methodology, a time-temperature equivalence principle of polymers is obtained from the requirement of group invariance of the field equations. A validation of this invariance principle is given by a comparison of the modelled master response and the master curve constructed from a set of experimental results at various temperatures. The extended direct method is next presented as a generalization of the direct method, in the sense that a classification of constitutive functions modelling the material behavior is achieved via a symmetry analysis. In the third part of the paper, the inverse problem of constructing a material's constitutive law exploiting a postulated Lie-group structure is exposed. A constitutive model is then identified which satisfies the symmetries exhibited by the experimental data. © Springer Science+Business Media B.V. 2009.

Bernard B.,CEA Le Ripault | Bianchi L.,CEA Le Ripault | Malie A.,SNECMA | Schick V.,LEMTA ENSEM | Remy B.,LEMTA ENSEM
Proceedings of the International Thermal Spray Conference | Year: 2015

Over many years, the aeronautic industry has been involved in Thermal Barrier Coatings (TBCs) development to increase the performances of the hot section components of aero engines like turbine blades or nozzle guide vanes. The Electron Beam Physical Vapor Deposition (EB-PVD) process has been widely used for high performances TBC's on metallic substrate mainly due to enhanced life time performances. Nevertheless, the cost, a rather high thermal conductivity and a poor resistance against chemicals aggressions of TBCs performed by EB-PVD are real drawbacks for the next generation of turbine engines. For this purpose, Suspension Plasma Spraying (SPS) has been employed in this study for TBC. It is showed that SPS process allows to performing columnar microstructure easily tunable in terms of: size, distribution and morphology. © Copyright (2015) by ASM International All rights reserved.

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