Le travail présenté dans ce mémoire est une contribution à l'étude des problèmes variationnels qui englobent les problèmes d'optimisation avec ou sans contraintes, les problèmes d'équilibre économique et de jeux, les problèmes de résolution d'équations et inéquations aux dérivées partielles, ainsi que de nombreux autres problèmes. La résolution d'une inéquation variationnelle comporte des difficultés liées d'une part au choix de l'algorithme de résolution, et d'autre part aux propriétés vérifiées par l'opérateur impliqué dans l'inéquation variationnelle. Dans ce mémoire, on propose de résoudre une inéquation variationnelle en utilisant l'algorithme itératif bâti sur le principe du problème auxiliaire ou, à chaque pas, on résoud un problème auxiliaire de minimisation. Sous la seule hypothèse de monotonie simple de l'opérateur, on ne peut pas prouver la convergence de cet algorithme. L'apport original du travail porte sur la prise en compte d'hypothèses minimales dans le cadre d'opérateurs généraux. D'une part, on donne une preuve de convergence dans le cas où l'opérateur global est défini sur le produit de deux espaces de Hilbert; il vérifie l'hypothèse de Dunn partielle par rapport à sa première composante (et a fortiori il est simplement monotone) et la forte monotonie par rapport à la deuxième composante. Comme application de ce jeu d'hypothèses général, nous pouvons traiter le cas d'opérateurs simplement monotones grâce à un nouvel algorithme de résolution/régularisation simultanées (versions parallèle et séquentielle): en effet l'opérateur global ainsi obtenu vérifie essentiellement les propriétés précédemment indiquées. D'autre part, on démontre la convergence du même algorithme dans le cas ou l'opérateur vérifie des hypothèses encore plus faibles que précédemment : on ne suppose même pas la monotonie globale de l'opérateur mais seulement la forte monotonie par rapport à la deuxième composante et l'hypothèse de Dunn pour l'opérateur emboité. La preuve que nous donnons se limite ici au cas particulier des opérateurs affines en dimension finie et sans contrainte d'ensemble admissible. ce travail est complété par des études numériques sur des exemples qui échappent typiquement aux jeux d'hypothèses rencontres dans des travaux antérieurs sur le même sujet.

To extend the knowledge of complex distillation arrangements for the separation of ternary mixtures and make them closer to implementation in industry is the motivation of this thesis work. Some design, operation, and control aspects are analysed, having the conventional distillation arrangements as comparison basis. The DWC is a complex distillation arrangement very attractive in terms of energy and cost savings. However, the DWC require large columns in order to be economically advantageous. Therefore, this arrangement is more attractive when the energy cost is high compared to the trays cost. From rigorous simulations of different separation examples, some synthesis rules have been obtained.Designs that minimise the distillation cost have been given special importance. DWC design procedures reported in the literature were based on only two decision variables. A new procedure that uses three decision variables for design optimisation has been proposed. It has been seen that the use of three decision variables is important to avoid excluding possible optimum designs.The control of the DWC is more complex than the control of the other distillation arrangements because the DWC has more operation degrees of freedom. The approach in this work has been to solve the DWC control by levels: stabilisation, composition control, and optimising control. When the manipulated variables for DWC stabilisation control are the distillate and the bottoms flowrate, which is the most common stabilisation control structure in the literature, the DWC presents high directionality and interaction. Besides, this stabilisation control structure is not appropriate to the DWC because the DWC has typically high reflux ratios. When the manipulated variables for stabilisation control are the reflux flowrate and the boilup, the DWC has better controllability and larger stability margins. Linear analysis tools are useful to select the set of manipulated variables for the DWC composition control. The preferred set of manipulated variables and the controllability of the corresponding control structure depend on the nominal operation. The DWC has two extra operation degrees of freedom that permit an operation optimisation. This optimisation is used to minimise the boilup. At a non-optimal operation, the controllability is improved. Therefore, a trade-off appears between operation optimisation and controllability. Changes in the design of the DWC can be used to improve its controllability. High directionality is a problem associated to DWC that may be improved using a large number of trays. On the other hand, DWC optimal designs have an equilibrated distribution of distillation effort between sections which, if broken, may also present improve the controllability. As found for operation, also for design, leaving optimal conditions permits to improve the controllability. Alternatively, for the composition control of the DWC, Dynamic Matrix Control is analysed. It is found that DMC performs worse than the diagonal feedback control strategy. The DWC extra operation degrees of freedom can be used dynamically for optimising control. Due to a marked directionality found in the response surface, DWC operation may be kept close to optimal operation using only one of the operation degrees of freedom. Optimising control of the DWC through the feedback control of a variable that characterises the optimal operation is possible. Some measurable variables are able to maintain optimal conditions with certain accuracy.The controllability of the DWC is compared to the controllability of other distillation arrangements. In general, the complexity of a distillation arrangement makes its energy efficiency better and its controllability worse. However, important exceptions have been found: - The DWC may give important energy savings as well as the best controllability if it is operated at non-optimal conditions. - When the manipulated variables for stabilisation are internal flows (reflux rates and boilups), the controllability of the DWC is better than the controllability of the other distillation arrangements. The DWC controllability is found to be more interesting for long columns. Therefore, the DWC needs long columns to be really attractive in terms of energy as well as in terms of controllability. In the literature, DWC controllability was misevaluate. In this thesis work, it is seen that, thanks to the arrangement complexity, the DWC may give at the same time energy savings and a good controllability, what makes it very attractive. To know the influence of the non-modelled detail and to obtain experimental results for the DWC is the most important step in the way to DWC implementation in industry.

Reproduction de : Thèse de doctorat : Génie des procédés et de l'environnement : Toulouse, INPT : 2004. / Titre provenant de l'écran-titre. Bibliogr. 70 réf.

Thèse de doctorat : Génie biologique et médical. Optimisation : Paris 12 : 2004. / Thèse électronique uniquement consultable au sein de l'Université Paris 12 (Intranet). Titre provenant de l'écran-titre. Bibliogr. f. 142-158.

Thèse de doctorant : sciences. Génie électrique : Ecully, Ecole centrale de Lyon : 2006. Thèse de doctorant : sciences. Génie électrique : Universidade Federal de Santa Catarina : 2006. / 131 réf.

Thèse de doctorant : Sciences. Génie électrique : Ecully, Ecole centrale de Lyon : 2006. Thèse de doctorant : Sciences. Génie électrique : Universidade Federal de Santa Catarina : 2006. / Titre provenant de l'écran-titre. 131 réf.

Thèse doctorat : Informatique : Strasbourg 1 : 2006. / Titre provenant de l'écran-titre. Bibliogr.11 p.

Thèse de doctorat : Informatique : Evry-Val d'Essonne : 2009. / Titre provenant de l'écran-titre.

Reproduction de : Thèse de doctorat : Informatique : Clermont-Ferrand 2 : 2005. / Thèse avec deux annexes. Titre provenant de l'écran-titre. Bibliogr. p. 175-186.

This inter-disciplinary thesis is concerned with the production of polyunsaturated fatty acids (PUFAs) from newly isolated and identified alpine microalgae, and the optimization of the temperature, photon flux density (PFD), and carbon dioxide (CO2) concentration for their mass production in an airlift photobioreactor (AL-PBR). Thirteen strains of microalgae were isolated from the alpine zone in Canyon Creek, Canterbury, New Zealand. Ten species were characterized by traditional means, including ultrastructure, and subjected to phylogenetic analysis to determine their relationships with other strains. Because alpine algae are exposed to extreme conditions, and such as those that favor the production of secondary metabolites, it was hypothesized that alpine strains could be a productive source of PUFAs. Fatty acid (FA) profiles were generated from seven of the characterized strains and three of the uncharacterized strains. Some taxa from Canyon Creek were already identified from other alpine and polar zones, as well as non-alpine zones. The strains included relatives of species from deserts, one newly published taxon, and two probable new species that await formal naming. All ten distinct species identified were chlorophyte green algae, with three belonging to the class Trebouxiophyceae and seven to the class Chlorophyceae. Comparative study between the distribution of algae at Canyon Creek and Mount Philistine, another alpine region in New Zealand where algal distribution was studied in detail, revealed that algal distribution patterns in the New Zealand alpine zone are complex, with some taxa apparently widely distributed and others range restricted or rare (with the caveat that very few sites have been studied in detail). At least some of the differences between the two sites could be accounted for by geographic differences, resulting in contrasting environmental conditions such as rainfall. As hypothesized, alpine strains isolated from the Canyon Creek were rich in PUFAs. Eight among the ten strains have PUFA proportions higher than monounsaturated fatty acids and saturated FAs. In a comparison of FA profiles of Scenedesmaceae species from a hot environment (Algerian Sahara) with the Scenedesmaceae species from Canyon Creek, the latter revealed a much greater degree of unsaturation. In addition, the Canyon Creek strains contained some FAs (such as docosapentaenoic acid, DPA) that were absent from Saharan strains. Among the strains from Canyon Creek Lobochlamys segnis LCR-CC-5-1A was selected for optimization experiments on the basis of growth kinetics, temperature response and FA composition, of which 60% of total FAs were PUFAs. Of that 60%, the α-linolenic acid (ALA) content was 46%. Two identical 1.5 Liter AL-PBRs were used for culturing Lobochlamys segnis LCR-CC-5-1A to study the effect of CO2 concentration, PFD and temperature on specific growth velocity, production of PUFAs, omega-3 FAs and, specifically, the concentration of ALA. The concentrations of CO2 examined in this research were 1.5, 3.0 and 4.5% in air. Similarly, the reponses of the strain to seven different PFDs, namely 38, 77, 115, 178, 210, 236 and 253 µmol m-2 s-1 and six different temperatures, 5, 10, 15, 20, 25 and 30οC, were analyzed. The maximum specific growth velocities (µmax) of the cultures were calculated from the experimental data and the cell production rate was calculated from fitting logistic growth models to these data; the two were compared by converting the former to the latter. The significance of the tested parameters was assessed using ANOVA and Tukey tests. The optimum conditions assessed at lab scale for maximum production of biomass, PUFAs and ALA were found to be a CO2 concentration of 3.0%, temperature of 20°C, and PFD of 178 µmol m-2 s-1. Increasing biomass production has the effect of maximizing PUFA production because there was no significant increase in concentration of PUFAs, omega-3 FAs, or ALA under levels of CO2, temperature, and PFD differing from those under which maximum growth occurred.