Reconnaissance de documents assistée: architecture logicielle et intégration de savoir-faire

Cette thèse aborde la reconnaissance de documents suivant une approche assistée, qui vise à exploiter au mieux les compétences respectives de l’homme et de la machine. Nos contributions portent notamment sur les questions d’architecture logicielle soulevées par la mise en oeuvre de systèmes de reconnaissance de documents. Les avantages d’un environnement coopératif sont motivés par une analyse critique des systèmes actuels, et une projection sur les futures applications de la reconnaissance de documents. Diverses propositions concrètes sont émises sur la conduite du dialogue homme-machine, ainsi que sur les possibilités d’amélioration à l’usage. L’inventaire des données à gérer dans un système de reconnaissance est organisé de façon modulaire et homogène, et représenté à l’aide du format standard DAFS Sur le plan du contrôle, le système est décomposé selon une modélisation multi-agents. Cette découpe conceptuelle est alors simulée dans notre plateforme de développement, qui repose sur la programmation concurrente, distribuée, et multi-langages. Une solution expressive est proposée pour le couplage entre le noyau de l’application et l’interface graphique. Le prototype qui a servi à valider l’architecture est présenté. Notre architecture logicielle encourage l’exploitation du savoir-faire typographique, par l’intermédiaire d’un support de fontes standardisé. Ce rapprochement entre les deux disciplines profite à la fois à l’ergonomie, à la valorisation des résultats de reconnaissance, et aux méthodes d’analyse automatiques. Nous présentons une poignée d’analyseurs originaux, pour des tâches de reconnaissance de caractères, d’identification des fontes, ou de segmentation. Les expériences conduites en guise de première évaluation démontrent l’utilité potentielle de nos outils d’analyse. Par ailleurs, une contribution est apportée au problème de l’évaluation des performances de systèmes de reconnaissance assistée, avec l’introduction d’un nouveau modèle de coûts. Celui-ci intègre l’influence du comportement de l’utilisateur, de même que l’amélioration des performances liée au phénomène d’apprentissage incrémental. Notre modèle de coûts est utilisé dans des simulations, ainsi que dans des expériences mettant en jeu des analyseurs existants. Les observations mettent en évidence la dynamique particulière des systèmes assistés par rapport aux approches entièrement automatiques.This thesis addresses the question of document recognition with an assisted perspective advocating an adequate combination between human and machine capabilities. Our contributions tackle various aspects of the underlying software architecture. Both a study of existing systems and a projection on some future applications of document recognition illustrate the need of cooperative environments. Several mechanisms are proposed to drive the human-machine dialog or to make the recognition systems able to improve with use. The various data involved in a recognition system are organized in a modular and homogeneous way. The whole information is represented using the DAFS standard format. In our proposition, the control is decentralized according to a multi-agent modelling. This conceptual scheme is then simulated on our development platform, using concurrent, distributed, and multi-languages programming. An expressive solution is proposed for the coupling between the application kernel and a graphical user interface. A prototype is realized to validate the whole architecture. Our software architecture takes advantage of the typographical know-how, through the use of a standardized font management support. This integrated approach lets us enhance the ergonomy, extend the possible use of the recognition results, and redefine some recognition techniques. A few innovative analyzers are described in the field of optical character recognition, font identification, or segmentation. The first experiments show that our simple methods behave surprisingly well, with respect to what can be expected from the state of the art. Besides, we bring a contribution to the problem of measuring the performance of cooperative recognition systems, through the introduction of a new cost model. Our notations are able to describe assisted recognition scenarios, where the user takes part in the process, and where the accuracy is modified dynamically thanks to incremental learning. Our cost model is used both in simulations and in experiments implying existing analyzers. The dynamic aspects of assisted systems can then be observed

Contribution à l'étude de l'érosion de cavitation:mécanismes hydrodynamiques et prédiction

In the field of hydraulic power plant, the leading edge cavitation is often responsible of sever erosion which may cause a premature shutdown of energy production with costly consequences. This type of cavitation is characterized by an attached vapour cavity at the leading edge of the blades. Transient vapour vortices are generated and convected by the mean ow to the pressure recovery region where they collapse violently. The resulting water hammer pressure is responsible of material damage. In order to investigate the cavitation erosion problem, many theoretical and experi- mental research has been performed in hydrodynamics, mechanical science and metallurgy. We intend in the present work to describe the hydrodynamic attack and provide new mathematical model to characterize and predict the pressure impulses induced on solid surface by repeated collapses of transient cavities. First, the dynamics of a single vortex collapse is performed in the IMHEF Cavitation Vortex Generator. High speed visualization shows systematic rebound of such cavity after the collapse. This explosive rebound is due to the dissolved gas and leads to the generation of a strong shock waves which propagates in the liquid and the solid as well. Assuming Tait'equation for water, an estimation of the shock overpressure has been performed by image processing. Overpressure as high as 2 GPa has been thus measured. Furthermore, the maximum potential energy of the cavity and the uid corresponding to the maximum volume of the cavity stands as a good basis to characterize the collapse overpressure. Investigation of the shedding process by an attached cavity is carried out in the IMHEF High Speed Cavitation Tunnel on a 2D NACA009 blade. The hydrofoil is equipped with 30 piezo resistive pressure transducers. Beside the pressure acquisition, cavitation induced vibrations as well as the main cavity dimensions are synchronously acquired. Pressure spectra and cavitation patterns analysis leads us to consider the free and the forced regime of the main cavity. The forced regime occured when the von Karman vortices frequency matches the first natural frequency of the hydrofoil. In this case, the main cavity pulsation as well as the shedding process are modulated by the blade vibration fre- quency. In the free regime, the main cavity may be stable or unstable. Stable cavitation is characterized by small amplitude of the main cavity pulsation. In this case, the tran- sient cavities have a small size compared to the cavity length and the shedding process is highly instationnary. The unstable cavitation is characterized by large amplitude of main cavity pulsation. The shedding process is modulated by the main cavity pulsation witch is governed by a Strouhal like law. The Strouhal number depends on the incidence angle and stands between 0.2 and 0.32. The cavitation induced vibrations are found to be highly modulated by the main cavity pulsations. Envelope calculation of acceleration signals allows to identify the shedding frequency. This result is validated in a centrifugal pump model. In this case, vibration signal is found to be modulated by the blade passing frequency. Furthermore, we have shown that the use of two accelerometers allows a better cavitation detection through the coherence function corresponding to the acceleration envelopes in well chosen frequency band. Amplitude demodulation of vibration signals stands as a promising technique that may allow in short future the cavitation monitoring in hydraulic machines. Analysis of the previous results allows to build the model of Cavitation Erosion Power. This model is based on the assumption that the pressure aggressiveness of a single cavity is proportional to its potential energy. Furthermore, in the lake of direct measurements of the vapour volume of the transient cavities, the main cavity length is used to scale the dimension of the erosive cavities. The cavitation Erosion Power is related to the macroscopic parameters in a simple way. The validation of this model is performed in the case of isolated hydrofoil by assuming that the pressure uctuations downstream of the main cavity is characteristic of the cavitation aggressiveness. In hydraulic runners, the leading cavitation is often in the forced regime and the Strouhal law is no more available. In this case, the shedding frequency is unknown. In order to overcome this problem and calculate the cavitation erosion power, vibratory approach may be used to measure the shedding frequency