The present text, submitted to the University of Liège in fulfillment of the requirements for the degree of Docteur en Sciences de lIngénieur, aims at improving the understanding and description of air‐water interactions in transient flows. A particular emphasis is set on phenomena relevant in civil and environmental engineering, like rivers, pipes, and hydraulic structures. Theoretical results of this doctoral research may be summarized in two main propositions. First, I show that any mathematical model for free surface flows can be extended to pressurized flows. Second, the multiphase drift‐flux model is proven an adequate alternative to Navier‐ Stokes equations in civil and environmental engineering. These propositions underpin the development of original mathematical models and new computational codes (WOLF1D and WOLF IMPack). Validation and application on actual cases prove the efficiency of the new approach. Original concepts introduced in this thesis pave the way for further research on environmental flows, especially on the mathematical description of transport phenomena (pollutants, sediments) and heterogeneous interactions (vegetation, rough bed).

No description available.

During the earthquake in Japan and California in the 1990s, some weld beam-to-column connections had some cracks in heavy rigid frame steel building. Consequently it is required to assess the performance of the welded connection in term of rotation capacity and crack propagation strength. Some experimental tests have been performed. The weld connections were submitted to cyclic loading with increasing amplitude until macro crack event. However the crack phenomenon depends on many parameters: the geometry, the material, the welding process. For this reason, it is interesting to develop a finite element modeling of this connection to complete these experiments and perform a parametric study. The welded connection is modeled by three dimensional mixed solid elements. The constitutive law is elastoplastic with isotropic hardening identified for the base metal and the weld metal. The crack propagation is modeled by cohesive zone model. The parameters of the cohesive zone model have been identified by inverse method with the modeling of three point bend tests of a pre-cracked sample performed on the base and weld metal. The fatigue damage generated by the cyclic loading is computed by the fatigue continuum damage model of Lemaitre and Chaboche and it is coupled with the cohesive zone model. The damage and the crack propagation depend on the residual stresses generated by the welding process. They have been computed by a simulation of this process with a thermo mechanical finite element analysis. This thesis presents the used models and the results compared with the experimental tests.

The thesis deals with a numerical model based on the finite element method applied to the continuous casting process. This model has been developed and implemented in the LAGAMINE finite element code and two industrial applications of steel casting are presented to illustrate the possibilities of the model. The first chapter of the thesis introduces the continuous casting process from the industrial point of view, allowing the definition of the essential terminology and the industrial challenges. Then, the objectives of the model are detailed: the model is applied to the upper part of the caster (in the mould region) as well as the bending and straightening zones. Chapters two, three and four are dedicated to the theoretical developments of thermal aspects (phase transformations, thermal contraction, heat flow and thermal boundary conditions), mechanical aspects (generalized plain strain state, material constitutive law, ferrostatic pressure and mechanical contact) and the staggered analysis for thermal / mechanical coupling. In the two next chapters, some numerical results are shown. The model has been first applied to a 125mm square billet in the mould region. The industrial goal was to evaluate the effect of the mould taper on the cooling of the billet (temperature evolution, solid shell growing, stress and strain development). The second application focuses on the risk of transverse cracking during straightening of steel slabs and the effect of some local defects (reduction in secondary cooling, rolls locking or misalignment). The thesis ends with some conclusions and perspectives for the model.

Heat recovery steam generators (HRSG) play a very important role in combined cycle (CC) power plants, where steam is generated from a gas turbine exhaust and supplied at the appropriate pressure and temperature to steam turbines for further power generation. The power plants achieve an overall efficiency above 55% and are ideally suited for combined heat and power generation in utility systems. The performance of energy conversion is improved by reducing exergy losses which implies reducing the temperature difference between the combustion gas and the steam cycle. Thus recent HRSG designs include up to three pressure levels with reheat in the steam cycle for maximum energy recovery and the use of high pressure, high temperature superheater and reheater in CC plants. Super critical boilers are also conceivable. Since HRSG performance has a large impact on the overall efficiency of the CC power plant, an accurate simulation of the performance of the HRSG is necessary. We present a steady state HRSG model to support design and rating simulations of vertical units. The simulation model, called FELVAL, divides the boiler in its rows. The row model can also be divided several times following the tube length, to better estimate the fumes temperature distribution across the hot gas path. Another model, called SUFVAL, carries out the design as well as the automatic generation of the FELVAL units and all the needed connections. The log mean temperature difference (LMTD) method and the effectiveness-NTU (ε -NTU) method are alternatively used to compute the overall heat transferred in each part of the HRSG. The problem of convergence of boiler models with more than one row in parallel is discussed. Good initialisation of the different variables is crucial to obtain convergence. The models are tested on 2 references HRSG. The first one is an assisted circulation boiler that operates at 3 subcritical pressure levels. The second is a once through boiler able to operate above the critical pressure of water. These new models were introduced into a commercial software of data reconciliation (VALI of Belsim sa) already used by the engineering and design departments of a HRSG manufacturer. They thus have a general-purpose package enabling them to make design, data reconciliation and simulation with the same software. Moreover, the use of FELVAL model will enable them to simulate any type of boiler and to obtain informations on the change of the temperatures inside the heat exchangers. This information is crucial for well monitoring closely the operation of a boiler, and better understanding its behaviour. This knowledge improvement allows to limit the overdesign and the safety margins and to reduce the investment costs.

Quasars are among the most luminous and the most distant objects in the Universe. Consequently they are particularly interesting to probe its origin and to understand its evolution. However, the huge distances at which these objects are generally found prevent us from resolving their central regions so that we cannot directly check the validity of the geometrical as well as the dynamical models accounting for their observational properties (spectral energy distribution, line profiles, presence or absence of radio jets etc). In our thesis, we use two indirect observational techniques in order to constrain the existing models. These techniques which are particularly sensitive to the geometrical structure of the quasar emission regions are polarimetry and gravitational microlensing. In the first part of our thesis we study the correlation between the direction of the linear polarization and the orientation of the host galaxy/ extended emission that we determined on the basis of high resolution HST images. We show how this study enables us to bring new clues favoring the existence of a unification model for the Type 1 and Type 2 quasars. In the second part, we show how gravitational microlensing allows to constrain the geometry and size of the regions at the origin of the broad absorption lines observed in the spectrum of 10 to 20 % of quasars. For this purpose we build a radiative transfer code allowing to simulate the line profiles produced in a variety of realistic wind models. These models are then used to study the variations of line profiles induced by the transit of a gravitational microlens. This technique is finally applied to the case of the quasar H1413+117 in order to determine the geometry of the regions which produce the broad absorption lines.

Les hémorragies endométriales sont une cause fréquente de consultation gynécologique. Lapparition de ces saignements est probablement facilitée par des perturbations du développement et de la structure des vaisseaux, ce qui est également observé lors dun traitement avec un progestatif à long terme. Toutefois, la raison du déclenchement des hémorragies reste encore obscure. Le but de notre étude a été de développer un modèle de transplantation dendomètre humain chez des souris immunodéficientes afin de déterminer les mécanismes impliqués dans lapparition de saignements utérins lors des menstruations ou liés au traitement local continu par progestatif (lévonorgestrel). Dans ce travail, nous avons étudié les vaisseaux sanguins endométriaux (nombre, taille, maturation), lexpression des enzymes protéolytiques (métalloprotéinases matricielles ou MMPs) et des récepteurs hormonaux aux strogènes et à la progestérone en présence ou non dun progestatif (lévonorgestrel). Nous avons également étudié laction combinée du progestatif et dun inhibiteur de MMPs dans le but de prévenir les saignements utérins. La meilleure compréhension des mécanismes sous-tendant ces pathologies devrait ouvrir des nouvelles perspectives thérapeutiques que le modèle que nous avons mis au point permettra de tester.

Todays workers are living in a rapidly changing environment and adaptability has become one of the most valued competences. Because of economical competition, demands imposed on workers are getting more and more elevated. The opposition between constraints of efficiency, search for performance, workload and private life, combined with a loss in work meaning and in social support, contribute to expose workers to job stress and burnout. Besides dealing with high workload and exigencies of adaptability, workers are expected to create their own career opportunities and development. More specifically, in order to stay competitive, organizations need workers that are active and creative at work, workers that are ready to invest not only their time, but also their mind into their work. In other words, they need workers to be engaged in their work. Given this apparent opposition between increased risk for job stress and burnout on the one hand, and increased need of engaged workers on the other, it is necessary to investigate which conditions are prevalent in the development of those phenomena. In this thesis, we present a theoretical overview of burnout and engagement concepts (chapter1 and chapter2, respectively). We then expose how they are integrated into the theoretical framework of the Job Demands-Resources (JDR) model, and what criticism it can be addressed (chapter3). Chapter4 is dedicated to our research objectives, which are declined in five empirical studies. In study1(chapter5) and study2 (chapter6), we aim at validating the Positive and Negative Occupational States Inventory (PNOSI), a tool that was designed to measure positive and negative workers reactions to their working environment. Results indicate that the tool is composed of two factors, one measuring negative occupational state and the other measuring positive occupational state. This structure was replicated on a variety of samples. Negative occupational state can be conceived as an intermediate state occurring before burnout, while positive occupational state seems to be similar to work engagement. Both are different from commitment and workaholism. The impact of item wording, and interactions between items on the one hand and gender and age on the other were also investigated. In study3 (chapter7), we aim at validating the JDR model on three-wave longitudinal data that we collected among workers of a Belgian public administration. In addition, this study aims at validating the JDR model using predictors derived from stigma and social identity literature. Results indicate that perceived prejudice predicts higher burnout, whereas group identification predicts higher engagement. This was found above the effects of job demands and job resources, respectively. An interaction effect was also observed: among those who identify strongly to their occupational group, engagement was lower when workers also perceived high prejudice towards this group. Study4 and study5 also aim at validating the model using new types of predictors. Study4 (chapter8) more specifically focuses on the health-impairment process of the JDR model. It investigates whether person-related factors (namely workaholism) predict burnout in addition to job demands. Study4 also longitudinally testes whether job strain can indeed be considered as an intermediate state occurring in response to high job demands before burnout develops. We found that job strain acts as an intermediate, shorter term reaction to high job demands, before the occurrence of burnout. Results were mitigated as to the role of workaholism. It was hypothesized that this variable would initiate another kind of process, dealing with person-related issues. In study5 (chapter9), we focus more specifically on the energetic process, and investigate whether workers work-related personal demands (namely, the expectations they develop with regards to their own performance) predict engagement above the effects of job and personal resources. Results indicate that work-related personal demands predict high future engagement, above the impact of job and personal resources. However, no reciprocal impact of engagement was observed. We end this thesis with a discussion of our results and a general conclusion.

Traiter les problèmes que pose la mobilité urbaine aujourdhui nécessite entre autres, lélaboration dune banque de données complète, capable de supporter les analyses qualitatives et quantitatives du système de transport et den évaluer lévolution en rapport aux éventuels changements de lensemble du système urbain. Les données relatives au domaine des transports sont indispensables à lalimentation des modèles de trafic, à lanalyse de la mobilité globale et aux suivis et à la gestion des conditions découlement du trafic au travers dun réseau de transport donné, dans le temps et dans lespace (Taylor M. et al, 1996; Bonnel P., 2004). Cependant, ces données sont très souvent collectées séparément selon les objectifs poursuivis par le planificateur. En effet, la planification urbaine ou la planification des transports en commun présente des objectifs différents de celle, par exemple, des trafics routiers et autoroutiers (Meyer M. et al, 2001). Ces planifications seffectuent généralement sans trop tenir compte des interactions qui sétablissent entre elles. Ainsi, fournir des solutions adéquates aux problèmes de mobilité urbaine, nécessite la prise en considération des aspects environnementaux et de lensemble des caractéristiques de lespace urbain : le système de transport et le système des localisations et des activités socio-économiques (Cancalon F. et al, 1991 ; Bonnel P., 2004). Les solutions ainsi générées doivent provenir dune approche intégrée de la planification des transports (Meyer M. et al, 2001). De plus, il a été pris en considération des éléments de modélisation de données (les GIS-T models) développés par (Dueker et al, 1997). Cest dans cette optique que cette recherche se propose dappréhender la question de la mobilité urbaine par une approche systémique de lespace urbain. Celui-ci sera caractérisé par lensemble des données qui le constitue afin de mettre en lumière les relations qui sous tendent la structure urbaine en question. Il sera ainsi développé un modèle intégré de données nécessaires à lanalyse de la mobilité urbaine : MIDAM. Ensuite, sur la base de MIDAM et de la synthèse de la littérature en matière de données « transports » et sur les logiciels de gestion de trafic, il a été possible de démontrer la faisabilité dun outil intégré « VISUTRANS » pour le suivi des politiques de transports ; la modélisation et les effets des transports urbains sur lenvironnement. Enfin, une méthodologie pratique quant à la manière dappréhender la mobilité urbaine est proposée avec pour cas dapplication la ville de Liège - Belgique.

Le chat est la seule espèce animale qui développe spontanément une entité clinique similaire à bien des égards à lasthme allergique humain. Communément appelée « asthme félin » par homologie à la maladie humaine, cette entité pathologique est le résultat dune inflammation persistante des voies respiratoires, associée à des phases aiguës de bronchospasme, une hyperréactivité bronchique à des stimuli divers et dans les stades avancés à des remaniements tissulaires de la paroi bronchique (e.g., érosions épithéliales, hypertrophie de la musculature lisse, hyperplasie glandulaire). Des modèles dasthme félin, obtenus par sensibilisation expérimentale à un allergène, reproduisent la majorité des caractéristiques cliniques, fonctionnelles et lésionnelles de la maladie naturelle et sont au premier plan de la découverte de nouvelles stratégies thérapeutiques (i.e., cyclosporine A, corticostéroïdes oraux et inhalés, immunothérapie spécifique). De la pathogénie de lasthme, ressort toute limportance de dominer lobstruction récurrente des voies respiratoires. Même si les bronchodilatateurs inhalés sont recommandés dans la prise en charge des crises dasthme chez le chat, leur efficacité clinique reste incertaine et peu étayée. Ainsi, les principes actifs, les posologies et les protocoles thérapeutiques actuellement préconisés sont dans une large mesure empiriques et/ou extrapolés de la médecine humaine, et nécessitent dêtre validés dans des conditions expérimentales contrôlées. Nos travaux sinscrivent donc dans cette optique et visent à définir une approche thérapeutique tant préventive que symptomatique des crises de bronchospasme chez le chat, ainsi quune utilisation rationnelle des bronchodilatateurs à longue durée daction pour un contrôle optimal de linflammation asthmatique. Lors dune première étude, nous avons investigué lactivité in vitro, vis-à-vis du muscle lisse bronchique félin, de différentes agents bronchodilatateurs parmi lesquels des agonistes β2-adrénergiques (isoprotérénol, salbutamol [SAL], fénotérol, formotérol, salmétérol [SLM]), un anticholinergique (ipratropium bromide [IB]) et une méthylxanthine (théophylline). Tous ont produit une relaxation dose-dépendante de la musculature lisse bronchique, avec des spécificités propres en termes de puissance, defficacité ou dactivité intrinsèque. Sur une base comparative, le formotérol est le ß2-mimétique le plus puissant, et lisoprotérénol le plus efficace avec le fénotérol. Le fénotérol et le formotérol sont des agonistes complets des récepteurs ß2-adrénergiques, le SAL et le SLM des agonistes partiels. Tenant compte des résultats des essais in vitro et de la disponibilité de formulations administrables par aérosols dans lespèce féline, les effets bronchoprotecteurs (intensité, durée daction) de six médications inhalées ont été caractérisés chez le chat sain, en préambule à leur utilisation dans des conditions pathologiques. Un modèle de bronchoconstriction induite par le carbachol a été retenu dans le cadre de cette deuxième étude. Il ressort de cette étude que le SLM en aérosol-doseur (25µg) présente un effet bronchoprotecteur soutenu persistant 24 heures mais est aussi la médication la moins efficace. Le SAL et lIB (nébulisation ou aérosol-doseur) sont des bronchodilatateurs à courte durée daction (48 heures) dont lutilisation combinée en aérosol-doseur (SAL IB : 100µg/20µg) met en exergue une synergie daction. Les conditions naturelles étant souvent incompatibles avec une approche anticipative de la crise dasthme, les traitements instaurés sont davantage à visée curative que prophylactique. Dans une troisième étude, nous avons exploré les effets bronchorelaxants du SAL (100µg) et de lIB (20µg), administrés seuls ou en traitement combiné, sur une bronchoconstriction induite par un aéroallergène (Ascaris suum) chez des chats rendus expérimentalement asthmatiques. La technique dinhalation par aérosol-doseur a été privilégiée vu les effets synergiques de la combinaison « SAL IB » et lintérêt de cette voie dadministration dans la gestion à domicile des crises dasthme. Aux doses testées, les bronchodilatateurs inhalés nont exercé aucun effet notable, naffectant en rien la résolution du bronchospasme induit. Chez lhomme, les crises et les épisodes dexacerbation de lasthme sont fréquents dans le cours évolutif de la maladie. Aucune étude chez le chat asthmatique en crise aiguë (induite ou spontanée) natteste de lefficacité des corticostéroïdes inhalés ni ne mentionne dans ce contexte lintérêt scientifique dune association aux ß2-mimétiques à longue durée daction. Nous avons donc comparé les effets de la prednisolone orale (1mg/kg q12h) à ceux dune dose élevée de fluticasone inhalée, seule (500µg q12h aérosol-doseur) ou en traitement combiné avec du SLM (500µg/50µg q12h aérosol-doseur), sur la fonction et linflammation pulmonaires dans un modèle félin dasthme aigu. Cette quatrième étude a montré quune courte cure orale de prednisolone diminue significativement linflammation bronchique à éosinophiles. De fortes doses de fluticasone inhalée se sont avérées bénéfiques dans le contrôle de lhyperréactivité bronchique non spécifique, sans toutefois exercer des effets marqués sur linflammation bronchique sous-jacente. Combiner cette corticothérapie inhalée au SLM a permis dobtenir des effets anti-éosinophiliques accrus et comparables à ceux de la prednisolone orale. Aucune des médications testées na modifié significativement la réponse clinique et fonctionnelle consécutive à linhalation de lallergène. Létude précédente permet de supposer que le SLM potentialise lactivité anti-inflammatoire des corticostéroïdes inhalés et/ou est doté de propriétés anti-inflammatoires intrinsèques. Dans une cinquième étude, nous avons donc investigué les effets du SLM en monothérapie (50µg q12h aérosol-doseur) sur la fonction et linflammation pulmonaires. Il ressort de cette étude, conduite sur un modèle félin dasthme aigu, que le SLM en monothérapie nexerce pas deffet protecteur sur la survenue dun bronchospasme allergique et est dépourvu de tout effet anti-inflammatoire propre. Les résultats obtenus, dans les conditions expérimentales de nos essais, conduisent aux conclusions suivantes : 1) les bronchodilatateurs inhalés (SAL, IB, SLM) sont dune efficacité thérapeutique limitée dans la prévention et le traitement symptomatique du bronchospasme allergique chez le chat sensibilisé à Ascaris suum 2) en revanche, recourir au SLM comme thérapie adjuvante aux corticostéroïdes inhalés ouvre de nouvelles perspectives thérapeutiques dans le contrôle de linflammation et de lhyperréactivité bronchiques chez le chat asthmatique./The cat is the only animal species that spontaneously develops a clinical entity closely similar to human allergic asthma and commonly referred to as feline asthma. Feline asthma is a chronic inflammatory disease of the lower airways characterised by intermittent respiratory distress due to bronchoconstriction, non-specific bronchial hyperresponsiveness and airway remodeling at latter stages (e.g., epithelial erosions, smooth muscle hypertrophy, glandular hyperplasia). Based on experimental sensitisation to allergens, models of feline asthma mimic many clinical, functional and lesional features of the naturally developing condition. Moreover, development and implementation of feline asthma models have greatly facilitated the search for novel therapies (i.e., cyclosporin A, oral and inhaled corticosteroids, specific immunotherapy). In considering the pathogenesis of asthma, it is of major importance to control recurrent airway obstruction. Although inhaled bronchodilators are recommended for the management of acute asthmatic exacerbations in cats, their clinical efficacy remains uncertain and poorly documented. Most currently recommended drugs, dosages and therapeutic schemes are largely empirical and extrapolated from human medicine, and need to be further validated under controlled experimental conditions. Hence, our work was aimed at determining the potential of inhaled bronchodilators for preventive and curative treatment of acute bronchospasms in asthmatic cats as well as at exploring the benefit of using long-acting bronchodilators to optimally control the airway inflammation. In the first study, we investigated in vitro effects on isolated feline bronchi of different bronchodilating agents including β2-adrenergic agonists (isoproterenol, salbutamol [SAL], fenoterol, formoterol, salmeterol [SLM]), an anticholinergic (ipratropium bromide [IB]) and a methylxanthin derivative (theophylline). All compounds caused a dose-related relaxation of bronchial smooth muscle, each exhibiting specificities in terms of potency, efficacy and intrinsic activity. On a comparative basis, isoproterenol and fenoterol are the most efficacious β2-mimetics while formoterol is the most potent one. Fenoterol and formoterol act as full agonists of β2-adrenoceptors, SAL and SLM as partial agonists. Taking into account results from in vitro testing procedures and availability of aerosol formulations suitable for lung delivery in cats, we compared the antispasmodic effects (magnitude, duration of action) of six inhaled medications against carbachol-induced bronchoconstriction in healthy cats. This second study showed that SLM by metered-dose inhaler (25µg) has a sustained activity for as long as 24 hours but is also the least efficacious medication. SAL and IB (nebulisation or metered-dose inhaler) are short-acting bronchodilators (4-8 hours) whose combination delivered with a metered-dose inhaler (SAL IB: 100µg/20µg) exhibits a synergistic antispasmodic effect. In the natural disease, asthmatic crisis are difficult to predict in terms of occurrence. Therefore, therapeutic interventions are more curative than preventive. In a third study, we explored the bronchodilating effects of SAL (100µg) and IB (20µg), delivered either alone or as a combined therapy, on allergen-induced bronchospasms in Ascaris suum-sensitised cats. The inhalation technique using a metered-dose inhaler was retained given the synergistic effects of the combination SAL IB with this method and its therapeutic interest for at-home management of asthmatic crisis. At the tested doses, these bronchodilators failed to reverse allergen-induced bronchospasms in cats with experimental asthma. In human beings, crisis and exacerbations of asthma are frequent events in the natural course of the disease. Efficacy of inhaled corticosteroids in cats with acute asthmatic exacerbations (induced or spontaneous) has not yet been determined, nor the potential benefit of adding long-acting β2-agonists in this context. Thus, the fourth study was aimed at comparing the effects of oral prednisolone (1mg/kg q12h) with those of inhaled fluticasone at high doses, alone (500µg q12h metered-dose inhaler) or combined with salmeterol (500µg/50µg q12h metered-dose inhaler), on lung function and airway inflammation in a feline model of acute asthma. This study showed that a short course of oral prednisolone significantly reduced allergen-induced bronchial eosinophilic inflammation. High doses of inhaled fluticasone proved to be efficient for decreasing non specific airway hyperresponsiveness but failed to markedly reduce the underlying airway inflammation. Adding salmeterol to inhaled fluticasone led to anti-eosinophilic effects of the same magnitude as those found for oral prednisolone. None of these treatments improved clinical and functional responses to allergen exposure. According to the previous study, it may be that SLM has an anti-inflammatory effect on its own and/or functions as a steroid-potentiating agent. In a fifth study, we investigated the effects of salmeterol as monotherapy (50 µg q12h metered-dose inhaler) on lung function and airway inflammation in our feline model of acute asthma. This inhaled medication did not prevent occurrence of allergic bronchospasm in Ascaris suum-sensitised and challenged cats, nor did it possess intrinsic anti-inflammatory activity. Under our experimental conditions, the main results achieved led to the following conclusions: 1) the inhaled bronchodilators (SAL, IB, SLM) are of limited efficacy for the prevention and symptomatic treatment of allergic bronchospasm in cats sensitised to Ascaris suum; 2) in contrast, using salmeterol as adjuvant therapy to inhaled corticosteroids opens up new perspectives for the treatment of bronchial inflammation and hyperresponsiveness in asthmatic cats.