Éditeur(s) : Yale University
Résumé : Sea-surface temperature images of the coastal upwelling regions off Northwest Africa show that the core of upwelling is sometimes located far from the coast. This has been documented in three regions that share a common feature, namely a wide and shallow continental shelf. This upwelling feature plays a key role in the ecology of the Canary Current System. It creates an innerfront which provides retention for biological material, e.g. fish eggs and larvae, in the highly productive nearshore environment. An analytical model has been developed based on a two dimensional extension of Ekman's solution. The linear and steady response of a homogeneous ocean forced by an upwelling-favorable wind provides a mechanism for the upwelling separation from the coast. The merging of the surface and bottom Ekman layers induces a very weak cross-shore circulation and a "kinematic barrier" for the Ekman transport divergence. In the case of an alongshore wind, the barrier is located near the isobath h ≈ 0.4D, where D is the thickness of Ekman layers. This yields an upwelling cell which is essentially concentrated in the region 0.5D < h < 1.25D, with upwelling occurring preferentially near the isobath h ≈ 0.6D. It turns out that the cross-shore width of upwelling scales with D/S, the ratio of Ekman depth to bottom topographic slope. The application of this solution to real bathymetric profiles rationalizes, not only the offshore upwelling observations in Northwest Africa, but also the influence of topography on the cross-shelf structure of a wind-driven coastal upwelling. The model also quantifies the effect of the cross-shore wind component showing how it drives the nearshore pressure gradient adjustment and how it affects the upwelling. A linear numerical experiment reproduces the theoretical steady solution, thereby allowing investigation of the transient regime. Relaxation of the hypothesis in the numerical model validates the linear assumption of the theory and then allows investigation of the sensitivity to friction parameterizations and the influence of stratification. The latter leads to an "oscillation" of the upwelling cell with seaward migration driven by outcropping and homogeneization of the water column, and, coastal incursion driven by a "boundary layers splitting" process caused by shoreward advection of the isopycnal dome and stratification of the inner shelf.
Journal of Marine Research (Yale University), 2008-09 , Vol. 66 , N. 5 , P. 589-616

Droits : 2008 Yale University
http://archimer.ifremer.fr/doc/2008/publication-6334.pdf
DOI:10.1357/002224008787536790
http://archimer.ifremer.fr/doc/00000/6334/

Éditeur(s) : American Geophysical Union
Résumé : As part of the French CLIPPER project, an eddy permitting model of the Atlantic circulation has been run for 22 years. The domain has open boundaries at Drake passage and at 30 degreesE, from Africa to Antarctica. The simulated mean circulation, as well as the eddy activity, is satisfactory for a 1/3 degrees model resolution, and the meridional heat transport at 30 degreesS is within the range estimated from observations. We use the "mixed" open boundary algorithm of Barnier et al. [1998], which has both a radiation condition and a relaxation to climatology. The climatological boundary forcing strongly constrains the solution in the whole domain. The model heat balance adjusts through the surface (heat flux retroaction term) more than the open boundaries. The radiation phase velocities calculated within the algorithm are analyzed. This shows, quite surprisingly, that both the eastern and western boundaries have a similar behavior, regardless of the preferred directions for advection (mainly eastward) and wave propagation (mainly westward). Our results confirm that open boundary algorithms behave differently according to the dynamics of the region considered. The passive boundary condition that Penduff et al. [2000] applied successfully in the north eastern Atlantic does not work in the present South Atlantic model. We emphasize the need for a careful prescription of the climatology at the open boundary, for which a new approach based on synoptic sections is implemented.
Journal of Geophysical Union - Research C - Oceans (0148-0227) (American Geophysical Union), 2001-10 , Vol. 106 , N. C10 , P. 22115-22129

Droits : 2001 American Geophysical Union
http://archimer.ifremer.fr/doc/2001/publication-454.pdf
DOI:10.1029/2000JC000376
http://archimer.ifremer.fr/doc/00000/454/

Éditeur(s) : HAL CCSD
Résumé : This work is devoted to the theoritical research and to the numerical calculus of weak solutions (in the sens of generalized functions) for the non linear transport equation((∂u)/(∂t))(x,y,t)+a(x,y,t)((∂f(u))/(∂x))(x,y,t)+b(x,y,t)((∂g(u))/(∂y))(x,y,t)=0 pour t>0with the initial condition u(x,y,0)=u₀(x,y) where the functions {(x,y,t)→a(x,y,t)} and {(x,y,t)→b(x,y,t)} belong to L^{∞}(R²×R⁺) (but can be discontinuous), the functions f and g are smooth and monotonous, the function {(x,y)→u₀(x,y)} belongs to L^{∞}(R²). We recall the necessary notions on nonlinear generalized functions for introducing their tensorial product. The main results (to determine the weak solutions) are sufficient conditions so that, when a sum of généralized functions (like Heaviside or Dirac products) is associated with zero, each terms of the sum is equal to zero. Thanks to these theoretical results, we can solve the Riemann problem with the help of a solver written like tensorial product of Heaviside functions (or like a sum of tensorial product of Heaviside functions) in order to obtain the weak solutions. These weak solutions allow to develop two dimensional numerical Godunov type schemes. Then, numerical tests are performed which give a comparison between the results obtained by these 2D schemes and the ones of the splitting method. These tests prove that the 2D numerical schemes are as reliable as the ones obtained by splitting. They are also more simple in their expression. Moreover, a more detailed comparative study of the two types of numerical schemes show that the 2D schemes are far less expensive in the linear case as well as in the non linear case. They are stable for the L^{∞} norm, unlike the splitting schemes. At least some perspectives as well as an existence theorem of a strong solution "almost eveywhere" for linear hyberbolic systems are studied.
Nous nous intéressons à la recherche et au calcul numérique de solutions faibles (au sens des fonctions généralisées) de l'équation de transport non linéaire((∂u)/(∂t))(x,y,t)+a(x,y,t)((∂f(u))/(∂x))(x,y,t)+b(x,y,t)((∂g(u))/(∂y))(x,y,t)=0 pour t>0complétée de la condition initiale : u(x,y,0)=u₀(x,y) où les fonctions {(x,y,t)→a(x,y,t)} et {(x,y,t)→b(x,y,t)} appartiennent à L^{∞}(R²×R⁺) (mais peuvent être discontinues), les fonctions f et g sont lisses et monotones, la fonction {(x,y)→u₀(x,y)} appartient à L^{∞}(R²). Des rappels sur les fonctions généralisées nous permettent d'introduire leur produit tensoriel. Un des résultats clés (pour déterminer ultérieurement les solutions faibles cherchées) donne des conditions suffisantes pour que, lorsqu'une somme de fonctions généralisées (de type produit d'Heaviside ou de Dirac) est associée à 0, chacun des termes de la somme est nul. Grâce à ces résultats théoriques, on résout le problème de Riemann 2D à l'aide d'un solveur s'écrivant comme produit tensoriel de fonctions type Heaviside (ou comme somme de produit tensoriel de fonctions type Heaviside) afin d'obtenir les solutions faibles. Ces solutions faibles permettent la construction des schémas numériques de type Godunov 2D. Nous les validons par des test numériques comparant les résultats obtenus par ces schémas 2D et ceux de la méthode du splitting. Ces tests montrent que les schémas numériques 2D sont aussi fiables que ceux par splitting, alors qu'ils sont plus simples dans leur écriture. Une étude comparative plus complète entre les deux types de schémas numériques montre de plus que les schémas 2D sont nettement moins coûteux à la fois dans les cas linéaire et non linéaire et qu'ils sont stables pour la norme L^{∞}, contrairement aux schémas par splitting. Enfin des perspectives ainsi qu'un théoréme d'existence de solutions fortes "presque partout" pour des systèmes hyperboliques linéaires sont abordés.
https://hal.archives-ouvertes.fr/tel-01487366

Droits : info:eu-repo/semantics/OpenAccess
tel-01487366
https://hal.archives-ouvertes.fr/tel-01487366
https://hal.archives-ouvertes.fr/tel-01487366/document
https://hal.archives-ouvertes.fr/tel-01487366/file/th%C3%A8se_olivier_jouannelle_HAL.pdf

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Previous work has demonstrated that geoelectrical measurements, acquired either along the Earth’s surface or in boreholes, can be sensitive to the presence of fractures. However, a lack of numerical approaches that are well suited to modelling electric current flow in fractured media prevents us from systematically exploring the links between geoelectrical measurements and fractured rock properties. To address this issue, we present a highly computationally efficient methodology for the numerical simulation of geoelectrical data in 2.5-D in complex fractured domains. Our approach is based upon a discrete-dual-porosity formulation, whereby the fractures and rock matrix are treated separately and coupled through the exchange of electric current between them. We first validate our methodology against standard analytical and finite-element solutions. Subsequent use of the approach to simulate geoelectrical data for a variety of different fracture configurations demonstrates the sensitivity of these data to important parameters such as the fracture density, depth, and orientation.
ISSN: 0956-540X

hal-01622151
https://hal.archives-ouvertes.fr/hal-01622151
https://hal.archives-ouvertes.fr/hal-01622151/document
https://hal.archives-ouvertes.fr/hal-01622151/file/sanzGJI2017.pdf
DOI : 10.1093/gji/ggx080

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In this paper we present a new local remeshing algorithm that is dedicated to the problem of erosion in finite element models whose grid follows the movement of the free surface. The method, which we name Surface Lagrangian Remeshing (SLR), is adapted to 2D Lagrangian models which couple surface erosion with deformation of Earth materials. The remeshing procedure preserves nodes defining the surface submitted to erosion and removes nodes belonging to surface elements whose internal angles or area is critically low. This algorithm is ideally suited to track long term surface evolution. To validate the method we perform a set of numerical tests, using triangular finite elements, which compare the results obtained with the SLR algorithm with global remeshing and with analytical results. The results show good agreements with analytical solutions. Interpolation errors associated with remeshing are generated locally and numerical diffusion is restricted to the remeshed domain itself. In addition this method is computationally costless compared to classical global remeshing algorithm. We propose to couple the SLR method with the Dynamical Lagrangian Remeshing (DLR) algorithm to enable local remeshing only of Lagrangian models coupling large deformation of Earth materials with large erosion.
ISSN: 0098-3004

hal-00639472
https://hal.archives-ouvertes.fr/hal-00639472
DOI : 10.1016/j.cageo.2010.05.023

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Properties of composite materials depend on interatomic phenomena occurring between binder crystals. Experimental information of Atomic Force Microscopy (A.F.M.) is of prime importance; however understanding is helped by molecular modeling. As underlined in Section 1, the present study is able to simulate crystal interfaces in presence of a solution within apertures less than 1 Nanometer at a full atomic scale. Section 2 presents the case study of a gypsum solution between (120) gypsum faces, with related boundary conditions and atomic interactions. Section 3 deals with the mass equilibrium of the solution within interfaces <5 angstrom, using the original Semi Analytical Stochastic Perturbations (SASP) approach. This information becomes in Section 4 the key for explaining the peak of adhesion obtained in A.F.M. around an aperture of 3 A and gives enlightenments on gypsum cohesion. In conclusion, this illustration shows the potentialities of full atomic modeling which could not be attained by any numerical approach at a mesoscopic scale.
ISSN: 0008-8846

hal-00411868
https://hal.archives-ouvertes.fr/hal-00411868
DOI : 10.1016/j.cemconres.2007.09.022

Résumé : Cette thèse à pour objet l'étude théorique et numérique de solutions dans les équations aux dérivées partielles non linéaires de la physique, en particulier en dynamique des fluides. La présence de discontinuités dans les solutions de ces équations complique la compréhension mathématique des phénomènes mis enjeu et leur traitement numérique, notamment en vue de simulations informatiques . Nous étudions ces équations par une méthode de régularisation dans un espace fonctionnel approprié. Lorsque des schémas numériques construits par des méthodes différentes conduisent à des résultats identiques, ceci jusque dans leurs moindres détails, il semble alors naturel de s'interroger dans quelle mesure ces suites de solutions numériques constituent une approximation d'une solution des équations étudiées. Nous construisons des suites de solutions approchées à partir d'un schéma numérique original,stable et suffisamment simple pour démontrer que ses suites constituent une méthode asymptotique de Maslov au sens des distributions en dimension trois d'espèce. La technique de régularisation employée consiste à étendre les variables réelles du problème ne des variables complexes, ce qui nous permet de construire des familles de solutions particulières que l'on ramène au cas réel en faisant tendre un petit paramètre vers O. Les solutions physiques recherchées apparaissent alors comme valeurs au bord de fonction holomorphes. Nous illustrons les résultats obtenus par des applications en cosmologie dans les cadres Newtoniens et relativistes pour des systèmes sans pression, puis avec pression et auto-gravitation, ainsi que pour le système des gaz parfaits.
This thesis is devoted to the theoretical and numerical study of singular solutions appearing in nonlinear partial differential complicates the mathematical understanding of the phenomena under concem as well as their numerical treatment, in particular in view of computation. These equations are studied by a regularization method in an appropriate functional space. When completely different numerical methods give the same results up to the smallest details one can reasonably expect that these numerical results suggest the existence of a mathematical solution of theses equations. We construct sequences of approximate solutions from an original numerical scheme, which is stable and simple enough to prove that these sequences constitute a Maslov asymptotic method in three space dimension. The regularization technique in use consits in extending the real variables of the problem into complex ones, which perrnits to construct families of particular equations that we bring back to the real case by letting a small paramater tend to zero. The expected physical solutions appear as boundary values of holomorphie functions . Illustrations are given by applications to cosmology in the Newtorian and re1ativistic settings for pressure1ess fluid dynamics, then in presence of self-gravitation and pressure as weil as for the systemof ideal gases

http://www.theses.fr/2011AGUY0478/document

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Many iterative processes can be interpreted as discrete dynamical systems and, in certain cases, they correspond to a time discretisation of differential systems. In this article the authors propose generating numerical methods in numerical linear algebra by modelling the linear system to be solved as a given state of a dynamical system; the solution can be reached asymptotically, as a (asymptotically stable) steady state, but also as a finite time (shooting methods). In that way, any (stable) numerical scheme for the integration of such a problem can be presented as a method for solving linear systems. The authors discuss aspects of this approach, which allows them to recover some known methods but also to introduce new ones. Finally, some convergence results and numerical illustrations are presented.
ISSN: 1017-1398

hal-00730194
https://hal.archives-ouvertes.fr/hal-00730194

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Experimentally Assisted Molecular Modelling (EAMM) is an original approach for predicting the structure of organic micro-crystals and deducing their habit in the presence of various solvents and additives. It is applied here in the case of n-octylamino-nitrobenzoxadiazole (nOA-NBD), a fluorescent compound. This general approach is first of all described and validated by its blind application to three known and closely-related crystals. Then, the whole process is applied to predict the molecular crystal generated by n-octylamino-NBD, including the molecule conformation, its structure (cell parameters, molecular packing, X-ray powder diagrams) and its theoretical plus actual habits in the presence of a solvent (p-xylene) and two additives (acetic acid and n-dodecane). The conformation of the predicted molecule is validated by comparison with two similar molecules embedded in observable crystals. Then, the choice between two proposed structures (with the same energy and two equiprobable packings) is based on the comparison between experimental and re-computed X-ray powder diffraction diagrams, and also on the interpretation of an actual TEM image in the light of the proposed cell parameters. This choice is confirmed by the comparison between the vapour-grown face development (proposed by the BFDH or the attachment energy models) and the actual face development in a pure solvent. Finally, the actual habit deduced from comparing the crystal attachment energy with the adsorption energy of solvent or additive molecules is validated by SEM images of NBD micro-crystals in presence of the solvent alone or in presence of both additives. In conclusion, the EAMM approach appears to be a decisive tool for quickly simulating structural and habit properties of the molecular crystals, accessible or not by experimentation. Thus, a numerical selection of molecules becomes possible in view of deriving organic materials with predetermined properties, such as the fluorescence properties of the compound considered in the present study.
ISSN: 0022-0248

hal-00857894
https://hal.archives-ouvertes.fr/hal-00857894
DOI : 10.1016/j.jcrysgro.2011.07.035

Éditeur(s) : HAL CCSD Society for Industrial and Applied Mathematics
Résumé : International audience
In this paper, we developed a theoretical study for nonconservative sytems in one dimension in order to construct numerical schemes for solving the Riemann problem. The nonconservative form of our model system required the use of a well-adapted theory in order to give us a sense of our problem. We chose a framework of generalized functions for solving a scalar hyperbolic equation with a discontinuous coefficient $sigma_t +usigma_x approx 0$, where u is the velocity solution of a Burgers's equation. After an explicit solution of the Riemann problem, we derived Godunov split schemes for computing an approximate solution of the Cauchy problem. We applied our study to a system modeling elasticity and a system modeling gas dynamics. Some stability properties of a scheme and its convergence to a generalized solution are proved for the first model. Numerical experiments confirmed this convergence result. For the second model, calculations of flows containing weak-to-moderate shocks showed that conservation errors are reduced when the mesh is refined but were not entirely eliminated.
ISSN: 0036-1429

hal-00770266
https://hal.univ-antilles.fr/hal-00770266
DOI : 10.1137/S0036142900378637

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
The paper is motivated by the long term safety analysis of the CO 2 geological storage. We present a methodology for the assessment of the ge-omechanical impact of progressive rock dissolution. The method is based on the use of X-ray tomography and the numerical dissolution technique. The influence of evolution of the microstructure on the macroscopic properties of the rock is analysed by using periodic homogenization method. The numerical computations show progressive degradation of all components of the stiffness (orthotropic) tensor. Moreover, the evolution of associated mass transfer properties (as tortuosity and conductivity tensors), by using the periodic homogenization method, is also calculated. The correlation between the mechanical parameters and the transfer properties during the dissolution pro-cess is presented. The results show that the highest increase of the hydraulic conductivity (in direction Y) is not associated with the highest decrease of Young modulus in this direction. Moreover, the highest decrease of Young modulus (in the direction X) is not associated with percolation in this direction. Finally, an incremental law to calculate settlement, in case of a rock with evolving microstructure, is proposed. The solution of the macroscopic settlement problem under constant stress and drained conditions showed that the geomechanical effects of the rock dissolution are rather limited.
ISSN: 0363-9061

hal-01104204
https://hal.archives-ouvertes.fr/hal-01104204
https://hal.archives-ouvertes.fr/hal-01104204/document
https://hal.archives-ouvertes.fr/hal-01104204/file/Numerical_computations_rock_dissolution_Wojtacki_al_2014.pdf
DOI : 10.1002/nag.2316

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The full numerical simulation of turbulent flows in the context of industrial applications remains a very challenging problem. One of the difficulties is the presence of a large number of interacting scales of different orders of magnitude, ranging from the macroscopic scale to the Kolmogorov dissipation scale. In order to better understand and simulate these interactions, new algorithms of incremental type have recently been introduced, stemming from the theory of infinite-dimensional dynamical systems (see, e.g., the algorithms of Foias, Jolly et al. (1988), Foias, Manley and Temam (1988), Laminie et al. (1993, 1994), Marion and Temam (1989, 1990), and Temam (1990)). These algorithms are based on decompositions of the unknown functions into a large- and a small-scale component, one of the underlying ideas being to approximate the corresponding attractor. In the context of finite element methods, the decomposition of a solution into small- and large-scale components appears when we consider hierarchical bases (Yserentant, 1986; Zienkiewicz et al., 1982). In the present article we derive several estimates of the size of the structures for the linear and nonlinear terms which correspond to interactions of different hierarchical components of the velocity field, and also their time variation. The one-step time variation of these terms can be smaller than the expected accuracy of the computation. Using this remark, we implement an adaptive spatial and temporal multilevel algorithm which treats differently the small- and large-scale components of the flow. We derive several a priori estimates in order to study the perturbation introduced into the approximated equations. All the interaction terms between small- and large-scale structures are frozen during several time steps. Finally, we implement the multilevel method in order to simulate a bidimensional flow described by the Burgers equations. We perform a parametric study of the procedure and its efficiency. The gain in CPU time is significant and the trajectories computed by our multi-scale method remain close to the trajectories obtained with the classical Galerkin method.
ISSN: 0168-9274

hal-00730710
https://hal.archives-ouvertes.fr/hal-00730710

Éditeur(s) : Springer
Résumé : Series of sensitivity tests were performed with a z-coordinate, global eddy-permitting (1/4 degrees) ocean/sea-ice model (the ORCA-R025 model configuration developed for the DRAKKAR project) to carefully evaluate the impact of recent state-of-the-art numerical schemes on model solutions. The combination of an energy-enstrophy conserving (EEN) scheme for momentum advection with a partial step (PS) representation of the bottom topography yields significant improvements in the mean circulation. Well known biases in the representation of western boundary currents, such as in the Atlantic the detachment of the Gulf Stream, the path of the North Atlantic Current, the location of the Confluence, and the strength of the Zapiola Eddy in the south Atlantic, are partly corrected. Similar improvements are found in the Pacific, Indian, and Southern Oceans, and characteristics of the mean flow are generally much closer to observations. Comparisons with other state-of-the-art models show that the ORCA-R025 configuration generally performs better at similar resolution. In addition, the model solution is often comparable to solutions obtained at 1/6 or 1/10 degrees resolution in some aspects concerning mean flow patterns and distribution of eddy kinetic energy. Although the reasons for these improvements are not analyzed in detail in this paper, evidence is shown that the combination of EEN with PS reduces numerical noise near the bottom, which is likely to affect current-topography interactions in a systematic way. We conclude that significant corrections of the mean biases presently seen in general circulation model solutions at eddy-permitting resolution can still be expected from the development of numerical methods, which represent an alternative to increasing resolution.
Ocean Dynamics (1616-7341) (Springer), 2006-12 , Vol. 56 , N. 5-6 , P. 543-567

Droits : © Springer 2006. Part of Springer Science+Business Media
http://archimer.ifremer.fr/doc/2006/publication-3514.pdf
DOI:10.1007/s10236-006-0082-1
http://archimer.ifremer.fr/doc/00000/3514/

Éditeur(s) : HAL CCSD
Résumé : International audience
This paper deals with variational inclusions of the form 0 2 f(x) + g(x) K where f is smooth function from a re exive Banach space X into a Banach space Y , g is a Lipschitz function from X into Y and K is a nonempty closed convex cone in the space Y . We show that the previous problem can be solved by an extension of the Zincenko's method which can be seen as a perturbed Newton's method. Numerical results are given at the end of the paper.
Revista Investigacion Operacional

hal-00924143
https://hal.archives-ouvertes.fr/hal-00924143

Éditeur(s) : Université des Antilles Études caribéennes
Résumé : En Haïti, rien ne semble être planifié et pensé sur le long terme, raison sans doute pour laquelle l’entrepreneuriat ne joue pas un rôle prépondérant dans le développement de l’économie du pays (Financial Times, 2015). Cette vision sur le court terme qui est celle de la majorité de la population -à savoir les pauvres- n’est cependant pas une vérité absolue puisque le groupe largement minoritaire de la population, les riches ou encore l’élite économique, compte des entrepreneurs au sens des pays riches, c'est-à-dire des personnes ayant une vision de l’entreprise sur le long terme avec pour perspective la croissance de l’entreprise et l’enrichissement personnel, parfois « saupoudré » ,ici et là, d’une touche sociale par rapport à la montée en puissance du phénomène Responsabilité Sociale des Entreprises (RSE). Ce numéro spécial sur l’entrepreneuriat en Haïti se veut force de propositions (pratiques) pour que l’entrepreneuriat ait droit de cité comme force motrice du développement d’Haïti. Si comme le dit l’entrepreneur Jerry Tardieu : investir et s’investir en Haïti est un acte de foi, que faire pour faire pour que l’entrepreneuriat soit un moteur de développement durable en Haïti ? Telle est la question centrale de ce numéro spécial. L’entrepreneuriat en Haïti a longtemps été marqué – notamment dans la partie formelle – par la dominance du commerce opéré pour une large part par des immigrés moyen-orientaux (Syriens, Libanais, etc.) et de grandes entreprises étatiques. L’économie haïtienne a entamé depuis les trois dernières décennies un élargissement de son entrepreneuriat à travers la privatisation des monopoles d’Etat et, récemment, se précise l’engouement des jeunes pour la création d’entreprises. Si pour certains analystes comme Lundahl (2010), l’entrepreneuriat communautaire a échoué en Haïti, il n’en demeure pas moins que la micro finance a connu un développement tel, qu’elle a démocratisé l’accès au financement et permis le développement d’une multitude de micro-entreprises (Paul, Daméus & Garrabé, 2011). In Haiti, nothing seems to be planned in advance. Everything seems to happen by chance, hence the reason why entrepreneurship is a heavy weight in the GDP of the country (Financial Times, 2015). This non strategic and short term vision of entrepreneurship in Haiti is peculiar to the vast majority of the population, that is to say the poor. However, this does not happen across the board as the rich (the minority of population) also called the ‘elite’ have a perception of entrepreneurship similar to developed countries where entrepreneurship is seen as a long term strategy with so called Corporate Social Responsibilities (CSR). This special issue about Haiti is to find practical solutions to ensure that entrepreneurship can play a major role in the economic development of the country. Jerry Tardieu, a Haitian entrepreneur, claimed that investing in Haiti is a proof of faith in the country’s potential. What can be done to turn entrepreneurship into a sustainable tool for the development of Haiti? This is the central research question of this special issue. For a while, leading entrepreneurs in Haiti were from the Middle East (Syria, Liban, etc) and public companies. However, over the last three years, entrepreneurs in Haiti have come from different backgrounds. Also, more and more young people are getting into entrepreneurship and many public companies have been privatised. Despite the fact that for some analyst’s entrepreneurship in Haiti has totally failed (Lundahl, 2010), the development of micro finance over the last few years has democratized access to funding, enabling development of a multitude of micro-enterprises (Paul & Dameus Garrabé, 2011) (Paul, Daméus & Garrabé, 2011). En Haití, nada parece estar planificado y pensado en el largo plazo, probablemente es la razón por la cual la iniciativa empresarial no está jugando un papel importante en el desarrollo de la economía (Financial Times, 2015). Esta visión a corto plazo es el de la mayoría de la población. Sin embargo, no es una verdad absoluta ya que el grupo de población en gran minoría, los ricos o la élite económica, los empresarios responsables de los efectos de los países ricos es decir, las personas con una visión de negocio a largo plazo con la perspectiva del crecimiento de la empresa y de enriquecimiento personal, aunque a veces 'salpicado aquí y allá de un toque social, en comparación con el aumento del fenómeno de la Responsabilidad Social Corporativa (RSC). Este número especial sobre el emprendimiento en Haití quiere suscitar propuestas (prácticas) para que la iniciativa empresarial llega a ser citada como una fuerza impulsora en el desarrollo de Haití. Si, como lo dice el empresario Jerry Tardieu, invertirse e invertir en Haití es un acto de fe, ¿que hacer para que el espíritu empresarial sea un motor para el desarrollo sostenible en Haití? Esta es la pregunta central de este número especial. Emprendimiento en Haití durante mucho tiempo ha sido etiquetado - sobre todo en la parte formal - por el predominio del comercio operado en gran parte por inmigrantes de Oriente Medio (Siria, Líbano, etc.) y las grandes empresas estatales. La economía haitiana ha comenzado las últimas tres décadas la expansión de la iniciativa empresarial a través de su privatización de los monopolios estatales y, desde hace poco, la moda de los jóvenes emprendedores. Aunque segun algunos analistas como Lundahl (2010), el emprendimiento comunitario no sucede Haití, el hecho es que las microfinanzas ha experimentado un desarrollo tal, se ha democratizado el acceso a la financiación, como permite el desarrollo de una multitud de microempresas (Paul & Dameus Garrabé, 2011).

Droits : info:eu-repo/semantics/openAccess
urn:doi:10.4000/etudescaribeennes.9541
http://journals.openedition.org/etudescaribeennes/9541

Éditeur(s) : HAL CCSD
Résumé : The geological storage of CO 2 is considered as one of the solutions to the problem of global warming. The most possible scenarios of geological behavior of soil in the long term conditions has to be precisely defined to avoid catastrophic damages in the future. Chemical properties of saline water in the aquifer after the CO 2 injection becomes more acidic with time. Therefore, chemical degradation of rock occurs, which leads to modifications of its mechanical properties (chemo-mechanical coupling) [1]. In this paper an incremental model of chemo-mechanical coupling using homogenization approach (asymptotic expansion method [2,3]) is proposed. The paper is focused on the numerical computations for the X-ray tomography image of carbonate rock microstructure [4]. The chemical degradation of the microstructure is obtained as a homogeneous dissolution in each direction (Fig.1. – Fig.2.) For every porosity state numerical computations to obtain full, orthotropic elasticity tensor are performed. Therefore, the degradations functions for all components of the rigidity tensor were defined (Fig.3.). Moreover, results of numerical calculations of diffusion, tortuosity and permeability tensors are presented [5,6]. The link between geometrical properties and mechanical and transport parameters are discussed. The numerical analysis of the carbonate rock sample in long term conditions shows the increase of porosity and associated mechanical weakening of the rock. Moreover, the increase of diffusion, tortuosity and permeability tensors elements with time were observed. Finally, the solution of the one-dimensional macroscopic problem of soil settlement due to chemical dissolution of rock at constant load is presented. The method is universal, in the sense that the non-dimensional time scale is used.
ALERT Workshop 2013
Aussois, France

hal-01103175
https://hal.archives-ouvertes.fr/hal-01103175

Éditeur(s) : HAL CCSD Editions Paralia CFL
Résumé : Des techniques d'optimisation de formes sont utilisées dans des problèmes du Génie Côtier pour la protection des plages. En collaboration avec le bureau d'étude Bas-Rhône Languedoc ingénierie, un projet d'aménagement concret de la plage du Lido de Sète, utilisant des ouvrages immergés en géotextile, a été étudié. Des solutions optimales, visant à réduire la mise en suspension des sédiments, pour les structures de défenses ont été obtenues à partir d'un modèle hydrodynamique de propagation de houle. Une étude complémentaire à partir d'un modèle de circulation et des travaux expérimentaux en canal à houle permettent ensuite de valider les résultats optimaux numériques obtenus. Shape optimization techniques, focusing on coastal structures design, are used to solve coastal engineering problem. In collaboration with the Bas-Rhône Languedoc engineering Company, a actual development plan concerning the beach of the Lido of Sète has been studied. Optimal solutions, aimed at reducing sediments suspended, for defense structures have been obtained with a hydrodynamic water wave model. An additional study using a circulation model and experimental works in flume tend to validate optimal numerical results.
ISSN: 1760-8716

hal-00854031
https://hal.archives-ouvertes.fr/hal-00854031
DOI : 10.5150/jngcgc.2008.025-I

Résumé : La thèse est consacrée à la recherche des catastrophes marines (tsunamis, ondes de tempête) dans les Antilles françaises, en utilisant des modèles analytiques et numériques de mécanique des fluides. L'accent est mis sur le développement de modèles de mouvement de glissements de terrain et des vagues causées par ces glissements. Le modèle le plus simple du glissement de terrain «solide block» est utilisé pour évaluer les caractéristiques des flux pyroclastiques du volcan Soufrière-Hills (Montserrat). Un modèle plus complexe de modélisation de glissement de terrain (modèle de Savage-Hutter) a été étudié analytiquement, donnant ainsi une nouvelle famille de solutions exactes décrivant le mouvement de l'écoulement par gravité non linéaire dans une vallée ou dans un canyon sous-marin. Le modèle comprend des ondes simples (Riemann waves),le cas d'un barrage qui cède (dam-break problem), des solutions auto-similaires dans la M-fonne et « chapeaux paraboliques ». Grâce à la théorie linéaire de l'eau peu profonde nous avons étudié le processus de génération de tsunamis par des glissements de terrain de volume variable, se déplaçant à une vitesse variable dans un bassin de profondeur variable. Dans le cas d'un fond marin particulier (cas sans "réflexion"), les phénomènes de résonnance ont été étudiés dans un bassin à profondeur variable. Nous avons utilisé des méthodes numériques pour la résolution non-linéaire des équations des eaux peu profondes afin d'analyser des catastrophes marines réelles (les ondes de tempête causées par le cyclone Lili en 2002, le tsunami volcanique de 2003 à Montserrat) et probables (un tsunami prés des côtes de la Martinique). Des données sur les catastrophes
The dissertation is devoted to research in the field of marine natural hazards (tsunamis, storm surges) in the French West Indies, using analytical and numerical models of fluid mechanics. Emphasis is placed on the development of models of landslide motion and generated tsunami waves. The simple "solid block" model is used to evaluate the characteristics of pyroclastic flow Soufriere Hills volcano (Montserrat). The "fluid model" of a landslide (so called Savage-Hutter model) is studied analytically; within this model a new family of exact solutions that describe the motion of nonlinear gravity flow in a valley or underwater canyon is found: nonlinear Riemann wave, dan break problem, self-similar solutions (M - wave and parabolic cap). In the framework of the linear shallow water theory the process of generation of tsunami waves by landslides of variable volume moving with variable velocity above the basin of variable depth is studied. For the specific bottom profile ("reflectionless" one) the resonant phenomena is investigated in the basin of variable depth. Numerical methods are used to analyze marine hazards: historical (storm surges, caused by Cyclone LILI in 2002; volcanic tsunami 2003 on Montserrat) and possible events (possible tsunami of the coast of Martinique). Various data on marine natural disasters are obtained during field surveys (volcanic tsunami in 2003, stonn surges caused by Hurricane Dean in 2007). Designed catalogs of tsunamis and storm surges are created based on results of numerical modeling and field studies; some statistical analysis is perfomed

http://www.theses.fr/2011AGUY0435/document

Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : We designed a thermo-mechanical numerical model for fast-spreading mid-ocean ridge with variable viscosity, hydrothermal cooling, latent heat release, sheeted dyke layer, and variable melt intrusion possibilities. The model allows for modulating several accretion possibilities such as the "gabbro glacier" (G), the "sheeted sills" (S) or the "mixed shallow and MTZ lenses" (M). These three crustal accretion modes have been explored assuming viscosity contrasts of 2 to 3 orders of magnitude between strong and weak phases and various hydrothermal cooling conditions depending on the cracking temperatures value. Mass conservation (stream-function), momentum (vorticity) and temperature equations are solved in 2-D cartesian geometry using 2-D, alternate direction, implicit and semi-implicit finite-difference scheme. In a first step, an Eulerian approach is used solving iteratively the motion and temperature equations until reaching steady states. With this procedure, the temperature patterns and motions that are obtained for the various crustal intrusion modes and hydrothermal cooling hypotheses display significant differences near the mid-ocean ridge axis. In a second step, a Lagrangian approach is used, recording the thermal histories and cooling rates of tracers travelling from the ridge axis to their final emplacements in the crust far from the mid-ocean ridge axis. The results show that the tracer's thermal histories are depending on the temperature patterns and the crustal accretion modes near the mid-ocean ridge axis. The instantaneous cooling rates obtained from these thermal histories betray these discrepancies and might therefore be used to characterize the crustal accretion mode at the ridge axis. These deciphering effects are even more pronounced if we consider the average cooling rates occurring over a prescribed temperature range. Two situations were tested at 1275-1125 °C and 1050-850 °C. The first temperature range covers mainly the crystallization range that is characteristic of the high temperature areas in the model (i.e. the near-mid-oceanic-ridge axis). The second temperature range corresponds to areas in the model where the motion is mainly laminar and the vertical temperature profiles are closer to conductive. Thus, this situation results in less discriminating efficiency among the crustal accretion modes since the thermal and dynamic properties that are described are common to all the crustal accretion modes far from the ridge axis. The results show that numerical modeling of thermo-mechanical properties of the lower crusts may bring useful information to characterize the ridge accretion structure, hydrothermal cooling and thermal state at the fast-spreading ridges and may open discussions with petrological cooling rate results.
ISSN: 1991-959X

hal-00907012
https://hal.archives-ouvertes.fr/hal-00907012
DOI : 10.5194/gmd-6-1659-2013

Éditeur(s) : HAL CCSD
Résumé : Today, one of the main challenges in the oil industry is the exploitation of new resources in naturally fractured reservoirs often located in structurally complex areas such as plate boundaries, mountain ranges or near salt structures. While numerical models of rock deformation based on continuum mechanics are becoming industry standard in providing efficient means for modelling natural fractures in reservoirs, the knowledge of past perturbed stress fields, which is referred as the type (normal, wrench or reverse), orientation and magnitude of the regional or local tectonic stresses that needs to be applied as boundary condition in numerical simulations, is often unknown or approximated.The essence of this thesis is to improve the recovery of the paleostress field needed to constrain numerical simulations. I first described and discuss through a comprehensive mechanically-based multi-parametric study how far we can rely on the commonly used paleostress inversion methods based on fault slip data and the Wallace and Bott assumptions. I then compared this method with a new generation technique based on geomechanics using field observations. Since slip markers on faults are hardly observed in core or image log, I used observed natural fracture data as main drivers for the inversion of the paleostress using geomechanically-based method. I demonstrated, through various outcrop and subsurface examples, how this can efficiently be done. Finally, I aimed at addressing the problem of polyphase fracture data sets with unknown mechanical type (joints, faults, stylolites ...) and expanded the mechanical stress inversion to the separation of tectonic phases.
Aujourd'hui, l'un des principaux défis dans l'industrie pétrolière est l'exploitation de nouvelles ressources dans les réservoirs naturellement fracturés souvent situés dans des zones structurellement complexes tels que les frontières de plaques, les chaînes de montagnes ou les structures de proches des dômes de sel. Alors que les modèles numériques de déformation des roches basée sur la mécanique des milieux continus fournissant des moyens efficaces pour la modélisation de fractures naturelles dans les réservoirs, sont devenus la norme dans l'industrie, les paléo-contraintes régionales ou locales appliquées comme condition aux limites dans les simulations numériques, définies par le régime (normal, décrochant ou inverse), l'orientation, et la magnitude des contraintes tectoniques, sont souvent inconnues ou approximées.L'essence de cette thèse est d'améliorer la prédiction du champ de paléo-contrainte nécessaire pour contraindre les simulations numériques. J’ai décrit dans un premier temps à travers une étude comparative multi-paramétrique complète basée sur la mécanique, dans quelle mesure nous pouvions compter sur les méthodes d'inversion des paléo-contraintes basées sur les hypothèses de Wallace et Bott et les données de glissement sur les failles. J’ai ensuite comparé ces méthodes avec une technique d’inversion de nouvelle génération basée sur la géomécanique en utilisant les observations de terrain. Puisque les marqueurs de glissement sur les failles sont rarement observés le long du forage, j’ai utilisé l’inversion géomécanique des contraintes pour les données de fractures naturelles observées. J’ai alors démontré, l’efficacité de cette technique à travers divers exemples d'affleurements et de subsurface. Enfin, j’ai proposé une solution afin de résoudre le problème des données de fractures polyphasées à type cinématique inconnu (joints, failles, stylolites ...) et étendu l’inversion de contrainte basée sur la géomécanique à la séparation des phases tectoniques.
https://hal.archives-ouvertes.fr/tel-01324110

tel-01324110
https://hal.archives-ouvertes.fr/tel-01324110
https://hal.archives-ouvertes.fr/tel-01324110/document
https://hal.archives-ouvertes.fr/tel-01324110/file/theselejri.pdf