Approche LPV pour la commande robuste de la dynamique des véhicules (amélioration conjointe du confort et de la sécurité)

Ce travail concerne le développement de méthodes de commandes avancées pour les suspensions automobiles afin d'améliorer la tenue de route des véhicules et le confort des passagers, tout en respectant les contraintes technologiques liées aux actionneurs de suspension (passivité, non-linéarités, limite structurelle). Dans la 1ère partie, nous proposons deux schémas de commande par approche LPV polytopique (Linéaire à Paramètre Variant) et Stabilisation Forte (Strong Stabilization) avec optimisation par algorithme génétique pour résoudre les conflits confort/tenue de route et confort/débattement de suspension. Dans la 2ème partie, pour résoudre le problème complet de commande de suspensions semi-actives, nous développons d'abord une stratégie générique pour les systèmes LPV généraux soumis à la saturation des actionneurs et à des contraintes d'état. Le problème est étudié sous la forme de résolution d'inégalités linéaires matricielles (LMI) qui permettent de synthétiser un contrôleur LPV et un gain anti wind-up garantissant la stabilité et la performance du système en boucle fermée. Ensuite, cette stratégie est appliquée au cas de la commande des suspensions semi-actives. Les méthodes proposées sont validées par une évaluation basée sur un critère industriel et des simulations effectuées sur un modèle non-linéaire de quart de véhicule.This work concerns the development of advanced control methods for automotive suspensions to improve road holding and passenger comfort, while satisfying the technological constraints related to the suspension actuators (passivity, nonlinearity, structural limit). In the first part, we propose two control schemes by polytopic LPV (Linear Parameter Varying) approach and by Strong Stabilization with genetic algorithm optimization to solve the comfort/handling and comfort/suspension travel conflits. In the second part, to solve the full semi-active suspension problem, we develop first a generic strategy for general LPV systems subject to actuator saturation and state constraints. The problem is studied in the form of resolution matrix of linear inequalities (LMI) that allows synthesizing an LPV controller and an anti-windup gain to ensure the stability and performance of the closed-loop system. Second, the theoretical result is applied to the case of semi-active suspension control. The proposed methods are validated by an evaluation based on an industrial standard and simulations on a nonlinear quarter vehicle model.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Stable ℋ∞controller design for systems with time delays

One of the difficult problems of robust control theory is to find strongly stabilizing controllers (i.e. stable controllers leading to stable feedback system) which satisfy a certain ℋ∞ performance objective. In this work we discuss stable ℋ∞controller design methods for various classes of systems with time delays. We consider sensitivity minimization problem in this setting for SISO plants. We also discuss a suboptimal design method for stable ℋ∞controllers for MIMO plants. © 2010 Springer-Verlag Berlin Heidelberg

On stable controller design for robust stabilization of time delay systems

This paper studies the problem of robust stabilization of an infinite dimensional plant by a stable and possibly low order controller. The plant of interest is assumed to have only finitely many simple unstable zeros, however, may have infinitely many unstable poles. In the literature, it has been shown that the problem can be reduced to an interpolation problem and it is possible to obtain lower and upper bounds of the multiplicative uncertainty under which an infinite dimensional stable controller can be generated by a modified Nevanlinna-Pick formulation. We propose that the same interpolation problem can be solved approximately by a finite dimensional approach and present a finite dimensional interpolation function which can be used to find a stable controller. We illustrate this idea by a numerical example and additionally show the effects of the free design parameters of the rational interpolating outer function approach on the numerical example. © 2015, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved

A theoretical study of aqueous humor secretion based on a continuum model coupling electrochemical and fluid-dynamical transmembrane mechanisms

Intraocular pressure, resulting from the balance of aqueous humor (AH) production and drainage, is the only approved treatable risk factor in glaucoma. AH production is determined by the concurrent function of ion pumps and aquaporins in the ciliary processes, but their individual contribution is difficult to characterize experimentally. In this work, we propose a novel unified modeling and computational framework for the finite element simulation of the role of the main ion pumps and exchangers involved in AH secretion, namely, the sodium-potassium pump, the calcium-sodium exchanger, the chloride-bicarbonate exchanger, and the sodium-proton exchanger. The theoretical model is developed at the cellular scale and is based on the coupling between electrochemical and fluid-dynamical transmembrane mechanisms characterized by a novel description of the electric pressure exerted by the ions on the intrapore fluid that includes electrochemical and osmotic corrections. Considering a realistic geometry of the ion pumps, the proposed model is demonstrated to correctly predict their functionality as a function of (1) the permanent electric charge density over the pore surface, (2) the osmotic gradient coefficient, and (3) the stoichiometric ratio between the ion pump currents enforced at the inlet and outlet sections of the pore. In particular, theoretical predictions of the transepithelial membrane potential for each simulated pump/exchanger allow us to perform a first significant model comparison with experimental data for monkeys. This is a significant step for future multidisciplinary studies on the action of molecules on AH production

Influence of inorganic solution components on lithium carbonate crystal growth

Lithium-bearing brines are an increasingly attractive source of Li for extraction. One extraction mechanism is the removal of Li from the fluid phase through the precipitation of zabuyelite (Li2CO3). The chemistry of the brine plays an important role in this process because ions in solution can compete for the components of the Li-carbonate phase. Here we explore the effect of different brine components on the precipitation of zabuyelite using experiments and computational simulations. Crystals formed in all solutions showed morphological evidence for potential transformation from a precursor phase. Our study indicates that Ca2+ and SO42– are incorporated into the precipitated zabuyelite crystals. Sulfate also interacts directly with specific surfaces on the growing crystal and is expected to form ion pairs with Li+ in solution. Similarly, Na+ appears to form ion pairs in solution with the carbonate ion, slowing nucleation of zabuyelite in the experiments. K+ and Cl– may interact with the growing zabuyelite crystals but do not appear to affect zabuyelite nucleation and growth times. These experiments highlight the importance of understanding the solution chemistry on zabuyelite formation in order to predict the efficiency of extraction processes and the purity of the solids

A thermodynamic framework for the modeling and optimization of crystallization processes

Crystallization is a widely used chemical engineering separation unit operation process. Since this technique can produce high purity products it is used for the industrial production of many chemical compounds, such as pharmaceuticals, agrochemicals, and fine chemicals. The production of these products is a multi-million dollar industry. Any methods to improve the production of these products would be highly valued. Thus, the main objective of this work is to target model-based optimal strategies for crystallization operations specifically targeting crystal size and crystal size distribution (CSD). In particular, take the knowledge gained and translate it into an economically and practically feasible implementation that is utilizable by the pharmaceutical industry. To achieve this, a comprehensive crystallization modeling framework is developed. This framework predicts the CSD while taking into account temperature, seeding variables, and antisolvent feed rates. In addition, this framework takes into account the recent proliferation of predictive thermodynamic solubility models. These solubility models have the potential to greatly reduce the need for experimental data, thus, improving the crystallization model’s predictive ability. Finally, these crystallization models are implemented into the gPROMS modeling software and are used for model-based optimization. The crystallization modeling framework is developed for several different scenarios. One framework consists of a full thermodynamic crystallization model for potassium chloride. This modeling framework when combined with model-based optimization is proven to be superior to heuristic methods. Another framework, which utilizes several different predictive thermodynamic solubility models, evaluates their use to predict crystallization behavior and to determine optimal operating conditions, cooling profiles, and antisolvent feed profiles. It is shown that these models can be used to determine optimal operating conditions and cooling profiles, but they are not sufficiently accurate to be used to determine optimal antisolvent feed profiles. The last crystallization framework is developed for the non-isothermal antisolvent crystallization of sodium chloride. This framework shows that for systems whose solute solubility is relatively independent of temperature, adding temperature control as a second degree of freedom is beneficial. In particular, it allows for the production of crystal mean sizes unattainable at other temperatures, and for the joint control of particle mean size and dispersion

Quantum Fields and Extended Objects in Space-Times with Constant Curvature Spatial Section

The heat-kernel expansion and $\zeta$-regularization techniques for quantum field theory and extended objects on curved space-times are reviewed. In particular, ultrastatic space-times with spatial section consisting in manifold with constant curvature are discussed in detail. Several mathematical results, relevant to physical applications are presented, including exact solutions of the heat-kernel equation, a simple exposition of hyperbolic geometry and an elementary derivation of the Selberg trace formula. With regards to the physical applications, the vacuum energy for scalar fields, the one-loop renormalization of a self-interacting scalar field theory on a hyperbolic space-time, with a discussion on the topological symmetry breaking, the finite temperature effects and the Bose-Einstein condensation, are considered. Some attempts to generalize the results to extended objects are also presented, including some remarks on path integral quantization, asymptotic properties of extended objects and a novel representation for the one-loop (super)string free energy.Comment: Latex file, 122 page

A THERMODYNAMIC DESCRIPTION OF CATION-RNA INTERACTIONS WITH DIFFERING ION ATMOSPHERE COMPOSITION

The charged nature of nucleic acids imposes a strong relationship between cations and RNA structure. As a result, RNA folding efficiency is highly dependent on the quantity and types of cations in solution. In vivo, there are a multitude of cations available to interact with RNA. The principal monovalent cation, K+, serves to neutralize most of the negative charges derived from nucleic acids. In addition, there are cations of higher valence that perform a number of important functions. Many studies have confirmed the ability of Mg2+ to promote native RNA structure. In addition to K+ and Mg2+, organic cations (polyamines) such as putrescine2+, spermidine3+, and spermine4+ are believed to be important for the process of RNA folding. All of these cations, both organic and inorganic, differ dramatically in both structural and physical properties. The purpose of the current work is to i) determine if organic and inorganic divalent cations stabilize the same folded state, ii) determine how different divalent ions interact with RNA to promote folding, and iii) develop an understanding of how the ion atmosphere is organized in the presence of three distinct types of cations (K+, Mg2+ and putrescine2+). To pursue these goals, a set of RNAs, all characterized at atomic resolution, were selected to represent a range of selectivity for inorganic ions. This structural information, combined with thermodynamic analyses looking at Mg2+ excess, thermal stability, ligand binding, and folding efficiency provide a comprehensive look at how ions stabilize the native state of RNA. We find that RNAs with Mg2+ chelation sites require either Mg2+ or Ca2+ to properly fold, while putrescine2+ can stabilize the native state of non-chelators, albeit to a lesser degree than Mg2+. Measurement of Mg2+ excess with the native and intermediate states shows that Mg2+ is more effective at stabilizing native structure due to a closer approach to the RNA surface. Therefore, organization of the ion atmosphere is dependent on the types of ions in solution as well as the conformation of the RNA