ParisTech National School of Bridges and Roads
Paris, France

École des Ponts ParisTech is a university-level institution of higher education and research in the field of science, engineering and technology.Founded in 1747 as the world's first engineering school, it remains to this day one of the most prestigious and selective French Grandes Écoles. Its historical mission was primarily to train engineering officials and senior civil engineers. The school now offers a wide-ranging education in civil engineering, mechanics, computer science, applied mathematics, finance, economics, urban studies, environment and transport engineering.It is headquartered in Marne-la-Vallée and is a founding member of ParisTech and of the Paris School of Economics.The school is under the Ministry of Ecology, Sustainable Development and Energy. Wikipedia.

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Cohen-Addad S.,CNRS Nanosciences Institute of Paris | Cohen-Addad S.,University Paris Est Creteil | Hohler R.,CNRS Nanosciences Institute of Paris | Hohler R.,University Paris Est Creteil | Pitois O.,ParisTech National School of Bridges and Roads
Annual Review of Fluid Mechanics | Year: 2013

Aqueous foams are complex fluids composed of gas bubbles tightly packed in a surfactant solution. Even though they generally consist only of Newtonian fluids, foam flow obeys nonlinear laws. This can result from nonaffine deformations of the disordered bubble packing as well as from a coupling between the surface flow in the surfactant monolayers and the bulk liquid flow in the films, channels, and nodes. A similar coupling governs the permeation of liquid through the bubble packing that is observed when foams drain due to gravity. We review the experimental state of the art as well as recent models that describe the interplay of the processes at multiple length scales involved in foam drainage and rheology. Copyright © 2013 by Annual Reviews. All rights reserved.

Delage P.,ParisTech National School of Bridges and Roads
Geotechnique | Year: 2010

Investigation of micro-macro relationships in soils most often concerns granular soils in which both the elemental unit (the grain) and the physical laws governing intergrain interactions appear to be better known. The situation is different for clays because the elementary unit and the inter-unit interactions at the micro-scale are more difficult to characterise. In fine-grained soils, it has been shown that an intermediate level, corresponding to the way clay and fine-grained particles are arranged together, had to be considered so as to link microscopic features to macroscopic behaviour. An investigation of the change in microstructure during compression carried out some time ago on a sensitive clay from Canada demonstrated that studying the changes in pore size distribution provides a satisfactory description of microstructure changes during compression. The analysis is applied here to six other sensitive clays. First, a careful examination of the intact and remoulded microstructure is conducted in order to understand better the relationship between microstructure and sensitivity. Second, an interesting correlation between the compressibility coefficient and the slope of the cumulative pore size distribution curve is observed in Champlain clays. This confirms the analysis conducted that compression in loose, lowplasticity soils can be attributed to the progressive and ordered collapse of pores, starting from the largest existing ones and progressively affecting smaller and smaller pores. A conclusion drawn from this work is that a micro-macro analysis in terms of changes of a rigid fragile porous matrix appears to be more relevant than a standard analysis based on the behaviour of individual grains, where the grains are taken to be the relevant elemental microstructure unit (a unit difficult to identify in natural clay soils). Also, further insight is provided for the interpretation of microstructure effects through comparing the compression curves of intact soil samples to those of remoulded samples.

Lecoeur E.,ParisTech National School of Bridges and Roads | Seigneur C.,ParisTech National School of Bridges and Roads
Atmospheric Chemistry and Physics | Year: 2013

A 9 yr air quality simulation is conducted from 2000 to 2008 over Europe using the Polyphemus/Polair3D chemical-transport model (CTM) and then evaluated against the measurements of the European Monitoring and Evaluation Programme (EMEP). The spatial distribution of PM2.5 over Europe shows high concentrations over northern Italy (36 μgm-3) and some areas of Eastern Europe, France, and Benelux, and low concentrations over Scandinavia, Spain, and the easternmost part of Europe. PM2.5 composition differs among regions. The operational evaluation shows satisfactory model performance for ozone (O3). PM2.5, PM10, and sulfate (SO= 4 ) meet the performance goal of Boylan and Russell (2006). Nitrate (NO- 3 ) and ammonium (NH+ 4 ) are overestimated, although NH+4 meets the performance criterion. The correlation coefficients between simulated and observed data are 63% for O3, 57% for PM10, 59% for PM2.5, 57% for SO=4 , 42% for NO- 3 , and 58% for NH+ 4 . The comparison with other recent 1 yr model simulations shows that all models overestimate nitrate. The performance of PM2.5, sulfate, and ammonium is comparable to that of the other models. The dynamic evaluation shows that the response of PM2.5 to changes in meteorology differs depending on location and the meteorological variable considered. Wind speed and precipitation show a strong negative day-to-day correlation with PM 2.5 and its components (except for sea salt, which shows a positive correlation), which tends towards 0 as the day lag increases. On the other hand, the correlation coefficient is near constant for temperature, for any day lag and PM2.5 species, but it may be positive or negative depending on the species and, for sulfate, depending on the location. The effects of precipitation and wind speed on PM2.5 and its components are better reproduced by the model than the effects of temperature. This is mainly due to the fact that temperature has different effects on the PM2.5 components, unlike precipitation and wind speed, which impact most of the PM2.5 components in the same way. These results suggest that state-of-the-science air quality models reproduce satisfactorily the effect of meteorology on PM2.5 and therefore are suitable to investigate the effects of climate change on particulate air quality, although uncertainties remain concerning semivolatile PM2.5 components. © Author(s) 2013.

Peigney M.,ParisTech National School of Bridges and Roads
Journal of the Mechanics and Physics of Solids | Year: 2013

This paper addresses the theoretical prediction of the quasiconvex hull of energy-minimizing (or stress-free) strains that can be realized by martensitic microstructure. Polyconvexification and related notions are used to derive some upper bounds (in the sense of inclusion) on the quasiconvex hull. Lower bounds are obtained from lamination techniques. The geometrically linear setting (infinitesimal strains) is considered in the present Part 2. Three-, four-, and twelve-well problems are considered. In particular, the structure of the set of energy-minimizing strains in cubic to monoclinic transformations is investigated in detail. That investigation is notably supported by three-dimensional vizualisations obtained by considering four-well restrictions. © 2013 Elsevier Ltd.

Peigney M.,ParisTech National School of Bridges and Roads
Journal of the Mechanics and Physics of Solids | Year: 2013

This paper addresses the theoretical prediction of the quasiconvex hull of energy-minimizing strains that can be realized by martensitic microstructures. Polyconvexification and related notions are used to derive some upper bounds (in the sense of inclusion) on the quasiconvex hull. Lower bounds are constructed by lamination techniques. The geometrically nonlinear theory (finite strains) is considered in the present Part 1. Analytical expressions are obtained for a three-well problem which encompasses the cubic to tetragonal transformation as a special case. Twelve-well problems related to cubic to monoclinic transformations are also studied. In that case, sufficient conditions are derived for the microstructure to be restricted to only two of the 12 wells. © 2013 Elsevier Ltd.

Nedjar B.,ParisTech National School of Bridges and Roads
International Journal of Solids and Structures | Year: 2011

In this work, a fully three-dimensional constitutive model suitable for the macroscopic description of unidirectional fibre-reinforced composites where the matrix exhibits a time-dependent viscoelastic behavior is developed. Specifically, we consider a coordinate-free formulation where the stress and strain fields can be decomposed into fibre-directional and volumetric parts on the one hand, and into extra contributions on the other hand. This offers an ideal framework where one can separate the fibres' contribution, considered here as time-independent and linearly elastic, and the matrix contribution that experiences creep only in shear. Among the many possibilities, we choose in this work a generalized Kelvin-Voigt rheological model to formulate the viscoelastic behavior of the matrix. Long-term as well as short-term relaxation processes can be integrated in the model by means of as many as necessary viscoelastic processes. The numerical discretization is described for an easy integration within a finite element procedure. Finally, numerical examples illustrate the possibilities of the present model. © 2011 Elsevier Ltd. All rights reserved.

Gabillet P.,ParisTech National School of Bridges and Roads
Energy Policy | Year: 2015

Through the analysis of energy supply choices, this article explores the way in which energy priorities and their climate-related features are incorporated into urban public policy. These choices must take account of different factors, as is the case with district heating, which is justified as a vehicle of renewable energy while subject to pressure in eco-districts because its techno-economic balances are destabilised by falls in demand. Our study focuses particularly on the city of Metz (France), which has chosen district heating as the primary source for provision for the municipal area and for its first eco-district. We analyse the tensions within these choices, with particular attention to the way in which they are negotiated inside municipal departments and with the local energy operator. This enables us to explore the tensions in defining the scale that governs decisions and the linkages between energy-related and urban priorities. © 2014 Elsevier Ltd.

Bocquet M.,ParisTech National School of Bridges and Roads | Bocquet M.,French Institute for Research in Computer Science and Automation
Quarterly Journal of the Royal Meteorological Society | Year: 2012

Atmospheric chemistry and air-quality numerical models are driven by uncertain forcing fields: emissions, boundary conditions, wind fields, vertical turbulent diffusivity, kinetic chemical rates, etc. Data assimilation can help to assess these parameters or fields of parameters. Because such parameters are often much more uncertain than the fields diagnosed in meteorology and oceanography, data assimilation is much more of an inverse modelling challenge in this context. In this article these ideas are experimented with by revisiting the Chernobyl accident dispersion event over Europe. A fast four-dimensional variational scheme (4D-Var) is developed, which seems appropriate for the retrieval of large parameter fields from large observation sets and the retrieval of parameters that are nonlinearly related to concentrations. The 4D-Var, and especially an approximate adjoint of the transport model, is tested and validated using several advection schemes that are influential on the forward simulation as well as on the data-assimilation results. Firstly, the inverse modelling system is applied to the assessment of the dry and wet deposition parameters. It is then applied to the retrieval of the emission field alone, the joint optimization of removal-process parameters and source parameters and the optimization of larger parameter fields such as horizontal and vertical diffusivities or the dry-deposition velocity field. The physical parameters used so far in the literature for the Chernobyl dispersion simulation are partly supported by this study. The crucial question of deciding whether such an inversion is merely a tuning of parameters or a retrieval of physically meaningful quantities is discussed. Even though inversion of parameter fields may fail to determine physical values for the parameters, it achieves statistical adaptation that partially corrects for model errors and, using the inverted parameter fields, leads to considerable improvement in the simulation scores. © 2011 Royal Meteorological Society.

Ghabezloo S.,ParisTech National School of Bridges and Roads
Cement and Concrete Research | Year: 2011

The effect of the variations of clinker composition on the poroelastic properties of class G oil-well cement pastes is studied using a multiscale homogenization model. The model has been calibrated in a previous work based on the results of a laboratory study. Various compositions of class G cements from literature are used in a hydration model to evaluate the volume fractions of the microstructure constituents of hardened cement paste. The poroelastic parameters such as drained bulk modulus, Biot coefficient, and Skempton coefficient are evaluated using the homogenization model. The results show that the variations in chemical composition of class G cements have no important effect on the variations of the poroelastic properties. © 2011 Elsevier Ltd. All rights reserved.

Ghabezloo S.,ParisTech National School of Bridges and Roads
Cement and Concrete Research | Year: 2011

The results of a macro-scale experimental study of the effect of heating on a fluid-saturated hardened cement paste are analysed using a multi-scale homogenization model. The analysis of the experimental results revealed that the thermal expansion coefficient of the cement paste pore fluid is anomalously higher than the one of pure bulk water. The micromechanics model is calibrated using the results of drained and undrained heating tests and permits the extrapolation of the experimentally evaluated thermal expansion and thermal pressurization parameters to cement pastes with different water-to-cement ratios. It permits also to calculate the pore volume thermal expansion coefficient αφ which is difficult to evaluate experimentally. The anomalous pore fluid thermal expansion is also analysed using the micromechanics model. © 2011 Elsevier Ltd.

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