Amélioration de la Modélisation et de la Simulation des Vêtements en 3D

Physically-based cloth modeling and simulation is a problem of interest for the scientific community interested in digital worlds. This thesis deals with the improvement of the mechanical modelling of fabric and with the recovering of its parameters for more realistic cloth animations.The general context of our work is modeling warp and weft textile materials using mass-spring systems. We propose a new non linear hysteretic model for fabric shear. Our model is based on binary springs and thus, allows saving computational time (no trigonometric computations). Our model mimics precisely the mechanical shear behavior of fabric measured from Kawabata machines. The transfert functions of springs are determined in such a way that if the numerical model of fabric is submitted to the same constraints as the real fabric in the Kawabata machines, we obtain the same curves as those produced by the real Kawabata experiment.We present also an experimental setup using motion capture system (MOCAP) to measure fabric viscosity parameters. Fabric viscosity parameters are computed using experimental data which allows to recover its damping parameters used in the Newton's equation of movement.Finally, we validate the whole mechanical model of fabric including its viscosity parameters through an experiment where we recover the geometry of a real piece of fabric hanging on a table using computer vision techniques, and by comparing this shape to the result obtained by our simulator running on the same piece of fabric and initialized with the same (almost) conditions as in the real experiment. Our computer vision technique is based on the POSIT calibration algorithm and a 3D stereo algorithm.La modélisation et la simulation réaliste de vêtements sur ordinateur prennent de plus en plus d'importance au sein de la communauté scientifique dans l'ère du tout numérique. Cette thèse se propose d'apporter des améliorations au niveau de la modélisation mécanique du tissu et de la détermination de ses paramètres afin de rendre les animations de vêtements plus réalistes.Nous nous plaçons dans le cadre de la représentation d'un tissu en chaîne et trame par un système "masses-ressorts" soumis aux lois de la dynamique. Nous proposons un modèle non linéaire hystérétique du cisaillement d'un tissu qui est avantageux en temps de calcul car il se base sur des ressorts linéiques et qui reproduit fidèlement le comportement mécanique mesuré par les machines de Kawabata. Les fonctions de transfert des ressorts ont été déterminés pour que le modèle de tissu numérique reproduise les courbes de Kawabata du tissu réel, quand le tissu virtuel est soumis aux mêmes contraintes que le tissu réel dans les machines de Kawabata.Nous proposons aussi un schéma expérimental utilisant un système de capture de mouvement (MOCAP) permettant de mesurer la cinématique d'un tissu en mouvement. La dynamique du tissu est calculée à partir des données expérimentales ce qui a permis de déterminer les paramètres de la dissipation visqueuse utilisés dans la loi de la mécanique.Enfin, nous avons pu valider notre modèle mécanique du tissu muni des paramètres trouvés avec la mise en place d'une technique de reconstruction 3D de la forme d'un tissu à partir de photographies, en se basant sur l'algorithme de calibration POSIT et sur un algorithme de reconstruction 3D par stéréovision. Nous pouvons ainsi comparer le drapé réel d'un tissu avec celui obtenu grâce à notre simulateur

Amélioration de la modélisation et de la simulation des vêtements en 3D

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Performance evaluation of concentrating solar photovoltaic and photovoltaic/thermal systems

International audienceHybrid conversion of solar radiation, which allows simultaneous conversion of sunlight into thermal and electrical energy in the photovoltaic/thermal collector, is one of the most promising techniques of solar energy exploitation. In this study, low concentrating photovoltaic (PV) and photovoltaic/thermal (PVT) systems were designed and tested for a given spring climatic condition of the Tunisian Saharan city Tozeur. The system is basically an asymmetric compound parabolic photovoltaic concentrator. As this system's performance deteriorates with rising the solar cells temperature, we proposed to convert it on a hybrid one in order to improve its electrical efficiency and to recuperate simultaneously thermal energy. The comparison of these systems operating confirmed the improvement of the electrical performance of the combined PVT system and its acceptable thermal energy production. A computational fluid dynamics ``CFD'' model which interprets the PVT system was then developed and validated against the experimental results, proving the validity of the developed model use to identify numerically this system limitations and predict the possible improvements. (C) 2013 Elsevier Ltd. All rights reserved

Performance evaluation of a solar photovoltaic system

The solar energy conversion into electricity is a very promising technique, knowing that the source is free, clean and abundant in several countries. However, the effect of the solar cells temperature on the photovoltaic panel performance and lifespan remains one of the major disadvantages of this technology. In this work, we present an experimental study of a particular photovoltaic panel. It is self-cooled due to its open design which facilitates natural ventilation helping to improve its performance mainly in hot hours of the day and to avoid dust accumulation on its surface. This solar system is tested for two soil natures, white and gray, and for two inclination angles, 0∘and 30°. Results show that the photovoltaic panel performs better when it is inclined and placed on a white soil. A 3D CFD model describing the performance of this solar system is then developed and a good agreement between the numerical results and experimental data is found. Similarly, this CFD model was used to compare the thermal performance of this solar system to that of the flat PV system and to show that its lower temperature allows better electrical production. Keywords: Solar photovoltaic system, Soil nature and inclination angle effect, Experimental characterization, CFD validation, Comparison of the CIGS PV and flat pane