Thèses : « Gradient-based model »

1

Ganguly, Sandipan. « Algorithmic Modifications to a Multidisciplinary Design Optimization Model of Containerships ». Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/32483.

Texte intégral

Résumé :

When designing a ship, a designer often begins with â an ideaâ of what the ship might look like and what specifications the ship should meet. The multidisciplinary design optimization model is a tool that combines an analysis and an optimization process and uses a measure of merit to obtain what it infers to be the best design. All that the designer has to know is the range of values of certain design variables that confine the design within a lower and an upper bound. The designer then feeds the MDO model with any arbitrary design within the bounds and the model searches for the best design that minimizes or maximizes a measure of merit and also meets a set of structural and stability requirements. The model is multidisciplinary because the analysis process, which calculates the measure of merit and other performance parameters, can be a combination of sub-processes used in various fields of engineering. The optimization process can also be a variety of mathematical programming techniques depending on the type of the design problem. The container ship design problem is a combination of discreet and continuous sub-problems. But to avail the advantages of gradient-based optimization algorithms, the design problem is molded into a fully continuous problem. The efficiency and effectiveness with which an optimization process achieves the best design depends on how well the design problem is posed for the optimizer and how well that particular optimization algorithm tackles the type of design problems posed before it. This led the author to investigate the details of the analysis and the optimization process within the MDO model and make modifications to each of the processes, so that the two become more compatible towards achieving a better final design. Modifications made within the optimization algorithm were then used to develop a generalized modification method that can be used to improve any gradient-based optimization algorithm.
Master of Science

Styles APA, Harvard, Vancouver, ISO, etc.

2

Käpernick, Bartosz [Verfasser]. « Gradient-based nonlinear model predictive control with constraint transformation for fast dynamical systems / Bartosz Käpernick ». Ulm : Universität Ulm, 2016. http://d-nb.info/1166756491/34.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

3

Poole, Adam James. « Macroscopic traffic model validation of large networks and the introduction of a gradient based solver ». Thesis, Durham University, 2017. http://etheses.dur.ac.uk/12430/.

Texte intégral

Résumé :

Traffic models are important for the evaluation of various Intelligent Transport Systems and the development of new traffic infrastructure. In order for this to be done accurately and with confidence the correct parameter values of the model must be identified. The focus of this thesis is the identification and confirmation of these parameters, which is model validation. Validation is performed on two different models; the first-order CTM and the second-order METANET model. The CTM is validated for two UK sites of 7.8 and 21.9 km and METANET for the same two sites using a variety of meta-heuristic algorithms. This is done using a newly developed method to allow for the optimisation method to determine the number of parameters to be used and the spatial extent of their application. This allows for the removal of expert engineering knowledge and ad-hoc decomposition of networks. This thesis also develops a methodology by use of Automatic Differentiation to allow gradient based optimisation to be used. This approach successfully validated the METANET model for the 21.9 km site and also a large network surrounding the city of Manchester of 186.9 km. This proves that gradient based optimisation can be used for the macroscopic traffic model validation problem. In fact the performance of the developed gradient method is superior to the meta-heuristics tested for the same sites. The methodology defined also allows for more data to be obtained from the model such as its Jacobian and the sensitivity of the objective function being used relative to the individual parameters. Space-Time contour plots of this newly acquired data show structures and shock waves that are not visible in the mean speed contour diagrams.

Styles APA, Harvard, Vancouver, ISO, etc.

4

Käpernick, Bartosz Maciej [Verfasser]. « Gradient-based nonlinear model predictive control with constraint transformation for fast dynamical systems / Bartosz Käpernick ». Ulm : Universität Ulm, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:289-oparu-8522-4.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

5

Patel, Kunal. « Stiffness Gradient Scaffolds as an In Vitro Model for Stem Cell Based Cardiac Cell Therapy ». University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1386725736.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

6

Hong, Jin Gi. « Development of process-based model and novel nanocomposite cation exchange membranes for salinity gradient power production ». Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53530.

Texte intégral

Résumé :

Ocean salinity is a renewable energy source that has not been recognized and could provide an opportunity to capture significant amount of clean energy when it mixes with river water. One of the processes emerging as a sustainable method for capturing energy from seawater is reverse electrodialysis (RED), which generates power via the transport of the positive and negative ions in the water through selective ion exchange membranes (IEMs). RED power generation is relatively close to commercialization, but its application is often limited by system power efficiency in natural water conditions. Although various types of salt ions exist in environmental saline water, most efforts have been focused on sodium chloride as a single ionic source in the water and the effects of other common multivalent ions (e.g., magnesium and sulfate) on power generation remain unexplored. Moreover, the commercial feasibility of RED is highly challenged by the absence of specialized RED membranes. Currently available IEMs are not optimized for RED power conversion systems, but successful operation is highly dependent on the membranes used. Major advances in manufacturing of proper IEMs will be a critical pathway to accelerate large-scale energy conversion by RED. Therefore, this study aimed at advancing our understanding of the RED power system for efficient and stable salinity gradient energy generation. Specifically, it is comprised of three parts. First, a mathematical model is developed for three different monovalent and multivalent ion combinations to determine the effect of different ionic compositions of the feed solution on the power density. Efforts are further made to optimize the RED system with respect to improving power density by investigating the sensitivity of key response parameters such as flow rate ratios and intermembrane distance ratios. Second, novel organic-inorganic nanocomposite cation exchange membranes (CEMs) are synthesized for RED application by introducing functionalized inorganic materials into an organic polymer matrix. The effect of inorganic particle filler loading within the organic polymer matrix on physico- and electrochemical performance is investigated. The results revealed that the increase of functionalized nanoparticle loading controls the effective ion transport in the membrane structure and there exists an optimum amount of nanoparticles (i.e., charged groups), which performs the best in selectively exchanging counter-ions, while excluding co-ionic species. Third, the membrane structure modification is demonstrated to enhance ion transport while maintaining large surface-charged functional groups in the polymer matrix. We have synthesized custom nanocomposite CEMs to tailor porous membrane structures of various thicknesses, aging (evaporation) time, and inorganic nanoparticle loadings. We have further tailored the membrane structure by incorporating different inorganic particle filler sizes. These engineered design approaches are found to be highly effective in obtaining desired physico- and electrochemical properties, which allowed higher ionic current flow throughout the system. Furthermore, for the first time we showed the successful application of tailor-made nanocomposite CEMs in a RED stack and achieved superb power density, which exceeds the power output obtained with the commercially available membranes. In summary, this dissertation has advanced our understanding of salinity gradient energy generation using RED technique. Specifically, computational modeling and simulation study investigates the development and optimization approaches of the RED process for practical application of RED using natural water conditions. Furthermore, the RED membranes developed in this dissertation focuses on fabrication, characterization, and optimization of cation exchange membranes. Overall, the results of this study are anticipated to benefit the future optimization of energy-capturing mechanisms in RED and provide the better pathway for the sustainable salinity gradient power generation.

Styles APA, Harvard, Vancouver, ISO, etc.

7

Zhang, Yi. « Strategies for Combining Tree-Based Ensemble Models ». NSUWorks, 2017. http://nsuworks.nova.edu/gscis_etd/1021.

Texte intégral

Résumé :

Ensemble models have proved effective in a variety of classification tasks. These models combine the predictions of several base models to achieve higher out-of-sample classification accuracy than the base models. Base models are typically trained using different subsets of training examples and input features. Ensemble classifiers are particularly effective when their constituent base models are diverse in terms of their prediction accuracy in different regions of the feature space. This dissertation investigated methods for combining ensemble models, treating them as base models. The goal is to develop a strategy for combining ensemble classifiers that results in higher classification accuracy than the constituent ensemble models. Three of the best performing tree-based ensemble methods – random forest, extremely randomized tree, and eXtreme gradient boosting model – were used to generate a set of base models. Outputs from classifiers generated by these methods were then combined to create an ensemble classifier. This dissertation systematically investigated methods for (1) selecting a set of diverse base models, and (2) combining the selected base models. The methods were evaluated using public domain data sets which have been extensively used for benchmarking classification models. The research established that applying random forest as the final ensemble method to integrate selected base models and factor scores of multiple correspondence analysis turned out to be the best ensemble approach.

Styles APA, Harvard, Vancouver, ISO, etc.

8

Verma, Navin Prakash. « Viscous Dampers for Optimal Reduction in Seismic Response ». Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/43716.

Texte intégral

Résumé :

To model dissipation of energy in vibrating civil structures, existence of viscous damping is commonly assumed primarily for mathematical convenience. In such a classical damper, the damping force is assumed to depend only on the velocity of deformation. Fluid viscous dampers that provide this type of damping have been manufactured to provide supplementary damping in civil and mechanical systems to enhance their performance. Some fluid dampers, however, exhibit stiffening characteristics at higher frequencies of deformation. The force deformation relationship of such dampers can be better represented by the Maxwell model of visco-elasticity. This model consists of a viscous dashpot in series with a spring, the latter element providing the stiffening characteristics. This study is concerned with the optimal utilization of such Maxwell dampers for seismic performance improvement of civil structures. The force deformation relationship of Maxwell dampers is described by a first order differential equation. Earlier studies dealing with these dampers, used an unsymmetric set of equations for combined structure and damper system. The solution of such equations for response analysis or for optimization calculation by a modal analysis approach would require the pair of the left and right eigenvectors. In this study, an auxiliary variable is introduced in the representation of a Maxwell damper to obtain symmetric equations of motion for combined structure and damper system. This eliminates the need for working with two sets of eigenvectors and their derivatives, required for optimal analysis. Since the main objective of installing these dampers is to reduce the structural response in an optimal manner, the optimization problem is defined in terms of the minimization of some response-based performance indices. To calculate the optimal parameters of dampers placed at different location in the structure, Rosen's gradient projection method is employed. For numerical illustration, a 24-story shear building is considered. Numerical results are obtained for seismic input defined by a spectral density function; however, the formulation permits direct utilization of response spectrum-based description of design earthquake. Three different performance indices -- inter story drift-based, floor acceleration-based, and base shear-based performance indices-- have been considered to calculate the numerical results. A computational scheme is presented to calculate the amount of total damping required to achieve a desired level of response reduction. The effect of ignoring the stiffening effect at higher frequencies in the Maxwell model on the optimal performance is evaluated by parametric variation of relaxation time coefficient. It is observed that the models with higher relaxation time parameter show a decreased response reducing damping effect. Thus ignoring the stiffening effect when it is, indeed, present would provide an unconservative estimation of the damping effect. The effect of brace flexibilities on different performance indices is also investigated. It is observed that flexibility in a brace reduces the effectiveness of the damper.
Master of Science

Styles APA, Harvard, Vancouver, ISO, etc.

9

Montebello, Claudio. « Analysis of the stress gradient effect in Fretting-Fatigue through a description based on nonlocal intensity factors ». Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLN019/document.

Texte intégral

Résumé :

Nous proposons dans ce manuscrit une nouvelle méthode pour prendre en compte l’effet du gradient en Fretting-fatigue. Les champs mécaniques présents à proximité du front de contact sont décrits à travers des facteurs d’intensité non locaux. L’objectif est d’aboutir à une description du champ de vitesse sous la forme d’une somme de termes exprimés chacun comme le produit d’un facteur d’intensité (Is, Ia, Ic), qui dépend des chargements macroscopiques appliqués à l’ensemble et d’une fonction de forme (ds, da, dc), qui est liée à la géométrie locale du contact. Cette description est obtenue à travers un processus non intrusif de post-processing des résultats obtenus avec des calculs à éléments finis. De plus, elle a été pensée pour être implémentée dans un contexte industriel. En pratique, pour chaque chargement macroscopique et pour chaque géométrie, il est possible de calculer un ensemble de facteurs d’intensité non locaux qui permettent de décrire les champs mécaniques locaux près du front de contact. Cette description non locale a l’avantage d’être (i) indépendante de la géométrie du contact employé et (ii) utilisable dans des modèles à éléments finis utilisés dans l’industrie qui sont caractérisés par des maillages plus grossiers par rapport à ceux utilisés pour étudier le fretting-fatigue dans des milieux académiques. Une étude est menée pour vérifier que les facteurs d’intensité non locaux peuvent être utilisés pour transposer les résultats expérimentaux d’une géométrie à une autre
In this manuscript a new method to describe the stress gradient effect in fretting-fatigue is proposed. It is based on the description of the mechanical fields arising close to the contact edges through nonlocal intensity factors. For this purpose, the kinetic field around the contact ends is partitioned into a summation of multiple terms, each one expressed as the product between intensity factors, Is, Ia, Ic, depending on the macroscopic loads applied to the mechanical assembly, and spatial reference fields, ds, da, dc, depending on the local geometry of the part. This description is obtained through nonintrusive post-processing of FE computation and is conceived in order to be easily implementable in the industrial context. As a matter of fact, for any given macroscopic load and geometry, a set of nonlocal intensity factors is computed that permits to characterize the mechanical fields close to the contact edges. Such nonlocal description has the advantage of being (i) geometry independent so that the nonlocal intensity factors can be used to compare laboratory test with real-scale industrial assembly, (ii) applicable to industrial FE models usually characterized by rougher meshes compared to the ones used to describe fretting-fatigue in the academic context. The procedure is applied to fretting-fatigue test data in order to verify whether the nonlocal intensity factors can be used to transpose experimental results to different contact geometries from the one in which they have been obtained

Styles APA, Harvard, Vancouver, ISO, etc.

10

Lebeda, Aleš. « Model soustavy motorů s pružným členem ». Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2012. http://www.nusl.cz/ntk/nusl-219693.

Texte intégral

Résumé :

This thesis deals with problem of experimental identification using principles of artificial intelligence and development of nonlinear models. It shows how to estimate parameters of nonlinear models and it compares different types of nonlinear models based on analytical analysis which were developed from measured data in simulation and real system motors with flexible component.

Styles APA, Harvard, Vancouver, ISO, etc.

11

Jolibois, Alexandre, et Alexandre Jolibois. « A study on the acoustic performance of tramway low-height noise barriers : gradient-based numerical optimization and experimental approaches ». Phd thesis, Université Paris-Est, 2013. http://pastel.archives-ouvertes.fr/pastel-00965168.

Texte intégral

Résumé :

Noise has become a main nuisance in urban areas to the point that according to the World Health Organization 40% of the European population is exposed to excessive noise levels, mainly due to ground transportation. There is therefore a need to find new ways to mitigate noise in urban areas. In this work, a possible device to achieve this goal is studied: a low-height noise barrier. It consists of a barrier typically less than one meter high placed close to a source, designed to decrease the noise level for nearby pedestrians and cyclists. This type of device is studied both numerically and experimentally. Tramway noise barriers are especially studied since the noise sources are in this case very close to the ground and can therefore be attenuated efficiently. The shape and the surface treatment of the barrier are optimized using a gradient-based method coupled to a 2D boundary element method (BEM). The optimization variables are the node coordinates of a control mesh and the parameters describing the surface impedance. Sensitivities are calculated efficiently using the adjoint state approach. Numerical results show that the shapes generated by the optimization algorithm tend to be quite irregular but provide a significant improvement of more than 5 dB (A) compared to simpler shapes. Utilizing an absorbing treatment on the source side of the barrier is shown to be efficient as well. This second point has been confirmed by scale model measurements. In addition, a full scale low height noise barrier prototype has been built and tested in situ close to a tramway track in Grenoble. Measurements show that the device provides more than 10 dB (A) of attenuation for a close receiver located at the typical height of human ears. These results therefore seem to confirm the applicability of such protections to efficiently decrease noise exposure in urban areas

Styles APA, Harvard, Vancouver, ISO, etc.

12

Jolibois, Alexandre. « A study on the acoustic performance of tramway low height noise barriers : gradient-based numerical optimization and experimental approaches ( Étude de la performance acoustique des écrans antibruit de faible hauteur pour le tramway : optimisation numérique par méthode de gradient et approches expérimentales) ». Thesis, Paris Est, 2013. http://www.theses.fr/2013PEST1116/document.

Texte intégral

Résumé :

Le bruit est devenu une nuisance importante en zone urbaine au point que selon l'Organisation Mondiale de la Santé, 40% de la population européenne est exposée à des niveaux de bruit excessifs, principalement dû aux transports terrestres. Il devient donc nécessaire de trouver de nouveaux moyens de lutter contre le bruit en zone urbaine. Dans ce travail, on étudie une solution possible à ce problème: un écran bas antibruit. Il s'agit d'un écran de hauteur inférieure à un mètre placé près d'une source, conçu pour réduire le niveau de bruit pour les piétons et les cyclistes à proximité. Ce type de protection est étudié numériquement et expérimentalement. Nous nous intéressons particulièrement aux écrans adaptés au bruit du tramway puisque dans ce cas les sources sont proches du sol et peuvent être atténuées efficacement. La forme ainsi que le traitement de surface de l'écran sont optimisés par une méthode de gradient couplée à une méthode 2D d'éléments finis de frontière. Les variables à optimiser sont les coordonnées de nœuds de contrôle et les paramètres servant à décrire l'impédance de surface. Les sensibilités sont calculées efficacement par la méthode de l'état adjoint. Les formes générées par l'algorithme d'optimisation sont assez irrégulières mais induisent une nette amélioration par rapport à des formes simples, d'au moins 5 dB (A). Il est également montré que l'utilisation de traitement absorbant du côté source de l'écran peut améliorer la performance sensiblement. Ce dernier point est confirmé par des mesures effectuées sur modèle réduit. De plus, un prototype à l'échelle 1 d'écran bas antibruit a été construit et testé en conditions réelles, le long d'une voie de tramway à Grenoble. Les mesures montrent que la protection réduit le niveau de 10 dB (A) pour un récepteur proche situé à hauteur d'oreilles. Ces résultats semblent confirmer l'applicabilité de ces protections pour réduire efficacement le bruit en zone urbaine
Noise has become a main nuisance in urban areas to the point that according to the World Health Organization 40% of the European population is exposed to excessive noise levels, mainly due to ground transportation. There is therefore a need to find new ways to mitigate noise in urban areas. In this work, a possible device to achieve this goal is studied: a low-height noise barrier. It consists of a barrier typically less than one meter high placed close to a source, designed to decrease the noise level for nearby pedestrians and cyclists. This type of device is studied both numerically and experimentally. Tramway noise barriers are especially studied since the noise sources are in this case very close to the ground and can therefore be attenuated efficiently. The shape and the surface treatment of the barrier are optimized using a gradient-based method coupled to a 2D boundary element method (BEM). The optimization variables are the node coordinates of a control mesh and the parameters describing the surface impedance. Sensitivities are calculated efficiently using the adjoint state approach. Numerical results show that the shapes generated by the optimization algorithm tend to be quite irregular but provide a significant improvement of more than 5 dB (A) compared to simpler shapes. Utilizing an absorbing treatment on the source side of the barrier is shown to be efficient as well. This second point has been confirmed by scale model measurements. In addition, a full scale low height noise barrier prototype has been built and tested in situ close to a tramway track in Grenoble. Measurements show that the device provides more than 10 dB (A) of attenuation for a close receiver located at the typical height of human ears. These results therefore seem to confirm the applicability of such protections to efficiently decrease noise exposure in urban areas

Styles APA, Harvard, Vancouver, ISO, etc.

13

Mhadji, Abdoussalam. « Développement d’un modèle à gradient d’endommagement pour la simulation de couplage thermique-mécanique : application à la dégradation des matériaux composites ». Electronic Thesis or Diss., Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2025. http://www.theses.fr/2025ESMA0002.

Texte intégral

Résumé :

L'utilisation de matériaux composites est courante dans les structures où la réduction de poids est essentielle, tout en maintenant des propriétés de rigidité et de résistance élevées. Cependant, ces matériaux sont inflammables, ce qui augmente les risques d'incendie. Il est généralement observé qu’un flux de chaleur provoque la transformation du matériau composite sain en charbon, ce qui entraîne une dégradation de ses propriétés mécaniques et une modification de ses propriétés thermiques initiales. Cependant, l’influence de l’hétérogénéité microstructurale sur la dégradation thermique, ainsi que le couplage entre cette dégradation et l’endommagement mécanique, demeurent peu étudiés dans la littérature. L'objectif de cette étude est d'analyser l'impact des mécanismes de dégradation, à la fois mécaniques et thermiques, sur différents phénomènes physiques tels que le transfert de chaleur, la décomposition thermique et la fissuration. Le but est de simuler l'interaction entre les différents modes de dégradation et leurs cinétiques, afin d’évaluer leur influence réciproque sur le comportement du matériau à l’échelle de la microstructure. Pour ce faire, une approche thermodynamique rigoureuse est adoptée, visant à introduire les variables internes correspondant à chaque phénomène physique, ainsi que leurs gradients. Cette démarche de modélisation associe deux approches : d’une part, un modèle à gradient de type champ de phase est employé pour décrire la dégradation thermique, évoluant selon une loi d’Arrhenius. Ce modèle permet de représenter avec précision l'interface entre les zones dégradées et intactes, tout en intégrant des informations liées à l'hétérogénéité de la microstructure et en suivant la propagation du front de décomposition, influencée par la morphologie. De plus, une étude expérimentale menée au sein du laboratoire a validé cette approche de modélisation, démontrant sa capacité à représenter de manière fidèle les phénomènes observés, notamment en ce qui concerne l'influence des variations microstructurales sur la dégradation des matériaux. D'autre part, un modèle à gradient d’endommagement basé sur le principe des puissances virtuelles distingue les forces thermodynamiques associées au processus réversible dérivant de l'énergie libre et les forces thermodynamiques associées au processus irréversible qui dérive cette fois du potentiel de dissipation. Ce choix de modélisation permet d'éviter les problèmes de localisation de l’endommagement et la dépendance au maillage. En couplant ces deux approches, il est possible de simuler l’interaction entre l’endommagement mécanique et la dégradation thermique du matériau. Les résultats montrent, d’une part, que les zones transformées en charbon deviennent des régions où l'endommagement et la fissuration s’initient facilement en raison de la dégradation des propriétés mécaniques. D’autre part, les zones endommagées ou fissurées agissent comme une barrière thermique, retardant la propagation de la chaleur. En effet, la présence de fissures réduit la conductivité thermique dans ces zones, limitant ainsi l'avancée du front thermique
The use of composite materials is widespread in structures where weight reduction is essential while maintaining high stiffness and strength properties. However, these materials are flammable, increasing fire risks. It is generally observed that heat flux transforms sound composite material into char, leading to the degradation of mechanical properties and a modification of initial thermal properties. Nevertheless, the influence of microstructural heterogeneity on thermal degradation, as well as the coupling between thermal degradation and mechanical damage, remains underexplored in the literature. The objective of this study is to investigate the influence of mechanical and thermal degradation mechanisms on physical phenomena such as heat transfer, thermal decomposition, and cracking. The study aims to simulate the interaction between different degradation modes and their kinetics to assess their mutual impact on the material’s behavior at the microstructural scale. To achieve this, a rigorous thermodynamic approach is adopted, introducing internal variables corresponding to each physical phenomenon, as well as their gradients. This modeling approach combines two methods: on the one hand, a phase-field gradient model is employed to describe thermal degradation, which evolves according to an Arrhenius law. This method is suitable for simulating phase transition phenomena and interface motion in a non-homogeneous material. This approach introduces a degradation gradient term to characterize the interface energy between degraded and sound regions, allowing the influence of microstructural fluctuations to be considered. On the other hand, a gradient damage model based on the principle of virtual powers distinguishes the thermodynamic forces associated with the reversible process, derived from free energy, from those associated with the irreversible process, derived from the dissipation potential. This modeling choice avoids issues related to damage localization and mesh dependency. By coupling these two approaches, it becomes possible to simulate the interaction between mechanical damage and thermal degradation of the material. The results show that, on the one hand, charred regions become areas where damage and cracking are easily initiated due to the degradation of mechanical properties. On the other hand, damaged or cracked zones act as thermal barriers, delaying heat propagation. Indeed, the presence of cracks reduces thermal conductivity in these regions, thereby limiting the advancement of the thermal front

Styles APA, Harvard, Vancouver, ISO, etc.

14

Reinecke, Robert [Verfasser], Petra [Akademischer Betreuer] Döll, Laura [Akademischer Betreuer] Foglia, Petra [Gutachter] Döll, Laura [Gutachter] Foglia et Thorsten [Gutachter] Wagener. « Beyond the bucket : development of a global gradient-based groundwater modeling software – its evaluation and integration into a global hydrological model / Robert Reinecke ; Gutachter : Petra Döll, Laura Foglia, Thorsten Wagener ; Petra Döll, Laura Foglia ». Frankfurt am Main : Universitätsbibliothek Johann Christian Senckenberg, 2020. http://d-nb.info/1206245948/34.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

15

Hendrickson, Jene Diane, et Soroosh Sorooshian. « CALIBRATION OF RAINFALL-RUNOFF MODELS USING GRADIENT-BASED ALGORITHMS AND ANALYTIC DERIVATIVES ». Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ), 1987. http://hdl.handle.net/10150/614186.

Texte intégral

Résumé :

In the past, derivative-based optimization algorithms have not frequently been used to calibrate conceptual rainfall -riff (CRR) models, partially due to difficulties associated with obtaining the required derivatives. This research applies a recently- developed technique of analytically computing derivatives of a CRR model to a complex, widely -used CRR model. The resulting least squares response surface was found to contain numerous discontinuities in the surface and derivatives. However, the surface and its derivatives were found to be everywhere finite, permitting the use of derivative -based optimization algorithms. Finite difference numeric derivatives were computed and found to be virtually identical to analytic derivatives. A comparison was made between gradient (Newton- Raphsoz) and direct (pattern search) optimization algorithms. The pattern search algorithm was found to be more robust. The lower robustness of the Newton-Raphsoi algorithm was thought to be due to discontinuities and a rough texture of the response surface.

Styles APA, Harvard, Vancouver, ISO, etc.

16

Priest, A. David. « The Development of an Average, Anatomically Based, Young Adult, GRIN Eye Model ». Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/1211.

Texte intégral

Résumé :

The purpose of this thesis is to describe the development of an anatomically based, young adult eye model, which includes a crystalline lens with a gradient refractive index (GRIN). This model will then be used to investigate the effect of laser refractive surgery. The first step in this process involved developing a symmetrical eye model that was found to be a better predictor of empirical longitudinal spherical aberration than any previous model. Myopia was simulated by either a purely axial or refractive technique. While these models were found to be good predictors of the spherical aberration measured in young adults, they did not predict the total amount of high-order aberrations. The techniques used to simulate a single type of myopia caused the myopic models to become anatomically inaccurate. To improve the eye models a biconic surface was used to quantify the anterior corneal shape as a function of myopia. A method to describe the refractive error and biconic shape parameters in Jackson Cross Cylinder terms was implemented to determine correlations. Results indicate that a biconic accurately models the average shape of the anterior corneal surface as a function of myopia. Adopting the biconic model for the anterior corneal surface and adding average misalignments of the ocular components transformed the models from symmetrical to asymmetrical. Refractive error was now simulated by the anatomically accurate changes in both the anterior corneal shape and axial length. The asymmetrical aberrations resulted from the misalignment of the ocular components and provided a good prediction of average empirical aberrations but underestimated the aberrations of individual subjects. Photorefractive keratectomy, a form of laser refractive surgery, was simulated by theoretically calculated and by empirically measured changes in the shape of the anterior corneal surface. Applying the change in anterior corneal shape to the asymmetrical models was used to develop postoperative models. Changes in corneal shape and model aberrations attributed to theoretical calculations do not match empirical observations. The prediction of increased high-order aberrations in postoperative models based on empirically measured changes in the anterior corneal topography was similar to clinical results. Average anatomically based, GRIN eye models have been developed that accurately predict the average aberrations of emmetropic and myopic young adults. These models underestimate the asymmetrical and total high-order aberrations that have been measured in individual subjects but are still useful for investigating the average effects of procedures like refractive surgery.

Styles APA, Harvard, Vancouver, ISO, etc.

17

Franken, Martina [Verfasser]. « Variational Discretization of Higher Order Geometric Gradient Flows Based on Phase Field Models / Martina Franken ». Bonn : Universitäts- und Landesbibliothek Bonn, 2013. http://d-nb.info/1044869364/34.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

18

Zhao, Ze. « Stochastic volatility models with applications in finance ». Diss., University of Iowa, 2016. https://ir.uiowa.edu/etd/2306.

Texte intégral

Résumé :

Derivative pricing, model calibration, and sensitivity analysis are the three main problems in financial modeling. The purpose of this study is to present an algorithm to improve the pricing process, the calibration process, and the sensitivity analysis of the double Heston model, in the sense of accuracy and efficiency. Using the optimized caching technique, our study reduces the pricing computation time by about 15%. Another contribution of this thesis is: a novel application of the Automatic Differentiation (AD) algorithms in order to achieve a more stable, more accurate, and faster sensitivity analysis for the double Heston model (compared to the classical finite difference methods). This thesis also presents a novel hybrid model by combing the heuristic method Differentiation Evolution, and the gradient method Levenberg--Marquardt algorithm. Our new hybrid model significantly accelerates the calibration process.

Styles APA, Harvard, Vancouver, ISO, etc.

19

Jin, Yabin. « Design of acoustic artificial structured materials : piezoelectric superlattice, gradient index lens, pillar based phononic crystal plate ». Thesis, Lille 1, 2017. http://www.theses.fr/2017LIL10011/document.

Texte intégral

Résumé :

Les cristaux phononiques et métamatériaux acoustiques sont des matériaux structurés artificiels qui fournissent un moyen prometteur pour manipuler les ondes acoustiques avec de nombreuses applications potentielles nouvelles. Après une introduction à l'état de l'art, le chapitre 2 propose des multicouches actives à base de structures piézoélectriques résonnantes. Leur transmission et leurs propriétés effectives peuvent être contrôlées activement en changeant les conditions électriques. Le chapitre 3 développe des méthodes d'homogénéisation pour une plaque de cristal phononique et montre pour la première fois la possibilité de contrôler simultanément la propagation de toutes les ondes fondamentales de Lamb. La méthode est appliquée à la conception de lentilles à gradient d'indice. Le chapitre 4 propose un nouveau type de cristal phononique en plaque à base de piliers creux qui met en évidence de nouveaux modes fortement localisés, tels que les modes de galerie, aussi bien dans le gap de Bragg que dans un gap à basse fréquence. Ces modes peuvent être activement accordés en remplissant les parties creuses des piliers avec un liquide dont on contrôle la hauteur ou la température. Le chapitre 5 propose une métasurface acoustique comportant un pilier unique ou une ligne de piliers déposés sur une plaque. Ces piliers ont des modes de résonance dipolaires et monopolaires qui sont très sensibles aux paramètres géométriques des piliers. Nous étudions en détail l'amplitude et la phase des ondes émises lorsqu'une onde incidente est diffusée par les piliers et montrons qu'elles peuvent être décrites comme des ondes émises par les piliers résonnants comme sources d'ondes acoustiques
Phononic crystals and acoustic metamaterials are artificial structured materials which provide a promising way to manipulate acoustic/elastic waves with many novel potential applications. After an introduction to the state of the art, the 2nd chapter designs actively controlled multilayers with piezoelectric resonant structures. The corresponding transmission and effective properties can be tuned by changing the electric boundary conditions of the piezoelectric materials. The 3rd chapter develops homogenization methods for phononic crystal plates and demonstrates for the first time the possibility of controlling simultaneously all the fundamental Lamb waves. The full control method developed here is applied to the design of various gradient index lenses that can exhibit several functionalities such as wave focusing or wave beaming. The 4th chapter designs a new type of phononic crystal/metamaterial plate with hollow pillars that exhibits several new localized modes, such as whispering-gallery modes, inside both Bragg and low frequency band gaps. These modes can be actively tuned by filling the hollow parts with a liquid for which the height or the temperature is controlled. The 5th chapter proposes acoustic metasurface consisting of a single pillar or one line of pillars deposited on a thin plate. Local resonances of dipolar and monopolar symmetries can be characterized which are very sensitive to the pillar’s geometric parameters. We study the amplitude and phase of the waves resulting from the scattering of an incident wave by the pillars and show that they can be described as dipolar or monopolar waves emitted by the pillar resonators as acoustic sources

Styles APA, Harvard, Vancouver, ISO, etc.

20

Dosne, Cyril. « Development and implementation of adjoint formulation of explicit body-force models for aero-propulsive optimizations ». Electronic Thesis or Diss., Institut polytechnique de Paris, 2024. http://www.theses.fr/2024IPPAX026.

Texte intégral

Résumé :

Dans le domaine de l’aéronautique civile, les études de plus en plus nombreuses portant sur les nouveaux systèmes moteurs, tels que les turbofans à très haut taux de dilution et les open-rotors, ainsi que sur les architectures d'intégration motrice innovantes, telles que la propulsion distribuée ou les systèmes à ingestion de couche limite, nécessitent une modélisation couplée de l’aérodynamique externe et du système propulsif, et ce dès les premiers stades de la conception. Les modèles body-force se sont avérés capables de reproduire fidèlement la majeure partie des phénomènes de couplage aéro-propulsif, comme la réponse aérodynamique du moteur aux distorsions d’entrée d’air, et ce à un coût de calcul réduit. Cependant, ils manquent d'une formulation adjointe pour être employés efficacement dans des optimisations par gradient. Cette thèse de doctorat se concentre sur le développement d'une approche adjointe pour les modèles body-force explicites. Tout d'abord, plusieurs optimisations aéro-propulsives sont menées sur une configuration académique de propulsion distribuée, à l'aide d'un modèle body-force réduit. Malgré la simplicité de ce modèle (d’intérêt pour les études de conception amont), une réduction de 10,5 % de la consommation de puissance est obtenue. Le potentiel de cette nouvelle méthodologie est ensuite évalué pour l'optimisation préliminaire de compresseurs, d'abord sans distorsion d’entrée d’air. Le modèle body-force de Hall est considéré pour cette étude. Les gradients de forme des aubes calculés à l’aide de l’adjoint body-force sont comparés à ceux obtenus via des simulations de haute-fidélité. Les résultats obtenus révèlent une très bonne capacité de prédiction des gradients du rotor par l’adjoint body-force, pour une grande partie de la caractéristique du compresseur, et particulièrement pour les points de fonctionnement situés entre le pompage et la zone de fonctionnement nominal du compresseur. En revanche, la précision de ces gradients est réduite à proximité du blocage. Pour le stator, seuls les effets liés à la désadaptation de l’aube au flux incident peuvent être captés. L’optimisation conduite avec l’adjoint body-force au point de fonctionnement nominal a permis d’améliorer le rendement du compresseur, ce qui a été confirmé par des simulations de haute-fidélité. Sous distorsion radiale, la méthode adjointe du body-force s’est à nouveau révélée capable d’améliorer les performances du compresseur en adaptant la géométrie des aubages aux perturbations d’entrée d’air. Les analyses haute-fidélité conduites sur les géométries obtenues par optimisations utilisant l’adjoint body-force montrent une augmentation du rendement isentropique comprise entre 1,16 et 1,47%, selon la formulation du problème d’optimisation retenue. Enfin, une optimisation du compresseur a été conduite à l’aide de l’adjoint body-force dans le cas d’une distorsion s’étendant sur la totalité de la circonférence de l’entrée d’air. Ces résultats sont très prometteurs et les observations effectuées sont cohérentes avec celles disponibles dans la communauté scientifique et obtenue à l’aide de calcul de haute-fidélité
In civil aviation, the increasing exploration of innovative engine systems – such as ultra-high bypass ratio turbofan or open-rotor – and breakthrough engine-integration architectures – such as distributed propulsion or boundary-layer ingestion – require a coupled modeling of the aerodynamic and propulsion subsystems from the earliest design stages. Body-force models have proven capable of faithfully reproducing most of the coupling phenomena, such as the engine response to inlet flow distortions, at reduced computational cost. However, they lack an adjoint formulation to be efficiently used in gradient-based optimizations. The present PhD thesis focuses on the development of an adjoint approach for explicit body-force models. First, aero-propulsive optimizations of an academic distributed propulsion configuration are conducted using a lumped body-force model. Despite the simplicity of this model (of interest for conceptual design studies), 10.5% decrease in power consumption is achieved. Then the potential of this new methodology is investigated for the preliminary optimization of compressor stages, at first under clean inflow conditions. The Hall body-force model is considered for such purpose. The comparison of the blade shape gradients computed by the adjoint body-force with high-fidelity ones, obtained from blade-resolved computations, shows very good prediction for the rotor. This is observed over a large portion of the compressor characteristic, especially between near-design and surge operating conditions, while accuracy is reduced near the blockage. On the contrary, for stator shape gradients, only flow misalignment effects can be captured. At design conditions, the improvement of the compressor efficiency obtained by the adjoint body-force optimization has been confirmed through high-fidelity simulations. Optimization under radial inlet distortion are then investigated. Once again, the adjoint body-force approach is found capable of enhancing the compressor performances, by adapting its geometry to the off-design inflow conditions. According to high-fidelity analysis of the body-force optimized blade geometry, an increase in compressor isentropic efficiency between 1.16 and 1.47% is achieved, given the formulation of the optimization problem. Finally, an optimization of the compressor under full-annulus inlet distortion is conducted leading to very promising results, which are consistent with those found in the literature using advanced simulations

Styles APA, Harvard, Vancouver, ISO, etc.

21

Capito, Ruiz Linda J. « Optical Flow-based Artificial Potential Field Generation for Gradient Tracking Sliding Mode Control for Autonomous Vehicle Navigation ». The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555599397128602.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

22

Bui, Manh-Tuan. « Vision-based multi-sensor people detection system for heavy machines ». Thesis, Compiègne, 2014. http://www.theses.fr/2014COMP2156/document.

Texte intégral

Résumé :

Ce travail de thèse a été réalisé dans le cadre de la coopération entre l’Université de Technologie de Compiègne (UTC) et le Centre Technique des Industries Mécaniques (CETIM). Nous présentons un système de détection de personnes pour l’aide à la conduite dans les engins de chantier. Une partie du travail a été dédiée à l’analyse du contexte de l’application, ce qui a permis de proposer un système de perception composé d’une caméra monoculaire fisheye et d’un Lidar. L’utilisation des caméras fisheye donne l’avantage d’un champ de vision très large avec en contrepartie, la nécessité de gérer les fortes distorsions dans l’étape de détection. A notre connaissance, il n’y a pas eu de recherches dédiées au problème de la détection de personnes dans les images fisheye. Pour cette raison, nous nous sommes concentrés sur l’étude et la quantification de l’impact des distorsions radiales sur l’apparence des personnes dans les images et nous avons proposé des approches adaptatives pour gérer ces spécificités. Nos propositions se sont inspirées de deux approches de l’état de l’art pour la détection des personnes : les histogrammes de gradient orientés (HOG) et le modèle des parties déformables (DPM). Tout d’abord, en enrichissant la base d’apprentissage avec des imagettes fisheye artificielles, nous avons pu montrer que les classificateurs peuvent prendre en compte les distorsions dans la phase d’apprentissage. Cependant, adapter les échantillons d’entrée, n’est pas la solution optimale pour traiter le problème de déformation de l’apparence des personnes dans les images. Nous avons alors décidé d’adapter l’approche de DPM pour prendre explicitement en compte le modèle de distorsions. Il est apparu que les modèles déformables peuvent être modifiés pour s’adapter aux fortes distorsions des images fisheye, mais ceci avec un coût de calculatoire supérieur. Dans cette thèse, nous présentons également une approche de fusion Lidar/camera fisheye. Une architecture de fusion séquentielle est utilisée et permet de réduire les fausses détections et le coût calculatoire de manière importante. Un jeu de données en environnement de chantier a été construit et différentes expériences ont été réalisées pour évaluer les performances du système. Les résultats sont prometteurs, à la fois en terme de vitesse de traitement et de performance de détection
This thesis has been carried out in the framework of the cooperation between the Compiègne University of Technology (UTC) and the Technical Centre for Mechanical Industries (CETIM). In this work, we present a vision-based multi-sensors people detection system for safety on heavy machines. A perception system composed of a monocular fisheye camera and a Lidar is proposed. The use of fisheye cameras provides an advantage of a wide field-of-view but yields the problem of handling the strong distortions in the detection stage.To the best of our knowledge, no research works have been dedicated to people detection in fisheye images. For that reason, we focus on investigating and quantifying the strong radial distortions impacts on people appearance and proposing adaptive approaches to handle that specificity. Our propositions are inspired by the two state-of-the-art people detection approaches : the Histogram of Oriented Gradient (HOG) and the Deformable Parts Model (DPM). First, by enriching the training data set, we prove that the classifier can take into account the distortions. However, fitting the training samples to the model, is not the best solution to handle the deformation of people appearance. We then decided to adapt the DPM approach to handle properly the problem. It turned out that the deformable models can be modified to be even better adapted to the strong distortions of the fisheye images. Still, such approach has adrawback of the high computation cost and complexity. In this thesis, we also present a framework that allows the fusion of the Lidar modality to enhance the vision-based people detection algorithm. A sequential Lidar-based fusion architecture is used, which addresses directly the problem of reducing the false detections and computation cost in vision-based-only system. A heavy machine dataset have been also built and different experiments have been carried out to evaluate the performances of the system. The results are promising, both in term of processing speed and performances

Styles APA, Harvard, Vancouver, ISO, etc.

23

Ghazlane, Imane. « Adjoint-based aerostructural sensitivity analysis for wing design ». Phd thesis, Université Nice Sophia Antipolis, 2012. http://tel.archives-ouvertes.fr/tel-00925210.

Texte intégral

Résumé :

Cette thèse a pour cadre le développement de méthodes numériques pour la conception optimale de forme de voilure en aérodynamique compressible. Ce travail a donné lieu au développement et à la validation d'un adjoint discret aéro-structure pour l'analyse de sensibilité par rapport aux paramètres de forme et de structure interne de l 'aile dont dépend la fonction d'intérêt, qu' elle soit aérodynamique ou structurale. Les développements logiciels ont été réalisés dans le code de simulation numérique de mécanique des fluides elsA et font suite aux travaux de Marcelet portant sur l'adjoint aéroélastique et dont ils sont une extension. Alors que pour l'adjoint aéro-élastique, on considère une aile flexible, de caractéristiques structurales constantes, pour l'adjoint aérostructure, leur variations sont prises en compte. Pour cela, l'extension de la méthode adjointe s' est accompagnée du développement d' un module de modélisation de la structure interne de l'aile. Ce module est linéarisé et vient donc alimenter le système adjoint. Il a été validé par le dimensionnement de la structure primaire d'une configuration de recherche fournie par l' avionneur Airbus. Dans l'état actuel de développement de la méthode adjointe dans le code elsA, on peut donc désormais calculer les sensibilités d'une fonction aérodynamique ou d'une fonction structure par rapport aux paramètres de forme aérodynamique ou de structure interne de l'aile. Le calcul des gradients ainsi obtenus a été validé par des comparaisons systématiques aux différences finies.

Styles APA, Harvard, Vancouver, ISO, etc.

24

Ghazlane, Imane. « Adjoint-based aerostructural sensitivity analysis for wing design ». Phd thesis, Nice, 2012. http://www.theses.fr/2012NICE4110.

Texte intégral

Résumé :

Cette thèse a pour cadre le développement de méthodes numériques pour la conception optimale de forme de voilure en aérodynamique compressible. Ce travail a donné lieu au développement et à la validation d'un adjoint discret aéro-structure pour l'analyse de sensibilité par rapport aux paramètres de forme et de structure interne de l 'aile dont dépend la fonction d'intérêt, qu' elle soit aérodynamique ou structurale. Les développements logiciels ont été réalisés dans le code de simulation numérique de mécanique des fluides elsA et font suite aux travaux de Marcelet portant sur l'adjoint aéroélastique et dont ils sont une extension. Alors que pour l'adjoint aéro-élastique, on considère une aile flexible, de caractéristiques structurales constantes, pour l'adjoint aérostructure, leur variations sont prises en compte. Pour cela, l'extension de la méthode adjointe s' est accompagnée du développement d' un module de modélisation de la structure interne de l'aile. Ce module est linéarisé et vient donc alimenter le système adjoint. Il a été validé par le dimensionnement de la structure primaire d'une configuration de recherche fournie par l' avionneur Airbus. Dans l'état actuel de développement de la méthode adjointe dans le code elsA, on peut donc désormais calculer les sensibilités d'une fonction aérodynamique ou d'une fonction structure par rapport aux paramètres de forme aérodynamique ou de structure interne de l'aile. Le calcul des gradients ainsi obtenus a été validé par des comparaisons systématiques aux différences finies.

Styles APA, Harvard, Vancouver, ISO, etc.

25

Liu, Lanfa, Manfred Buchroithner, Min Ji, Yunyun Dong et Rongchung Zhang. « Quantitative Retrieval of Organic Soil Properties from Visible Near-Infrared Shortwave Infrared (Vis-NIR-SWIR) Spectroscopy Using Fractal-Based Feature Extraction ». Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-220555.

Texte intégral

Résumé :

Visible and near-infrared diffuse reflectance spectroscopy has been demonstrated to be a fast and cheap tool for estimating a large number of chemical and physical soil properties, and effective features extracted from spectra are crucial to correlating with these properties. We adopt a novel methodology for feature extraction of soil spectroscopy based on fractal geometry. The spectrum can be divided into multiple segments with different step–window pairs. For each segmented spectral curve, the fractal dimension value was calculated using variation estimators with power indices 0.5, 1.0 and 2.0. Thus, the fractal feature can be generated by multiplying the fractal dimension value with spectral energy. To assess and compare the performance of new generated features, we took advantage of organic soil samples from the large-scale European Land Use/Land Cover Area Frame Survey (LUCAS). Gradient-boosting regression models built using XGBoost library with soil spectral library were developed to estimate N, pH and soil organic carbon (SOC) contents. Features generated by a variogram estimator performed better than two other estimators and the principal component analysis (PCA). The estimation results for SOC were coefficient of determination (R2) = 0.85, root mean square error (RMSE) = 56.7 g/kg, the ratio of percent deviation (RPD) = 2.59; for pH: R2 = 0.82, RMSE = 0.49 g/kg, RPD = 2.31; and for N: R2 = 0.77, RMSE = 3.01 g/kg, RPD = 2.09. Even better results could be achieved when fractal features were combined with PCA components. Fractal features generated by the proposed method can improve estimation accuracies of soil properties and simultaneously maintain the original spectral curve shape.

Styles APA, Harvard, Vancouver, ISO, etc.

26

Li, Yunming. « Machine vision algorithms for mining equipment automation ». Thesis, Queensland University of Technology, 2000.

Trouver le texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

27

Casero, Cañas Ramón. « Left ventricle functional analysis in 2D+t contrast echocardiography within an atlas-based deformable template model framework ». Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:b17b3670-551d-4549-8f10-d977295c1857.

Texte intégral

Résumé :

This biomedical engineering thesis explores the opportunities and challenges of 2D+t contrast echocardiography for left ventricle functional analysis, both clinically and within a computer vision atlas-based deformable template model framework. A database was created for the experiments in this thesis, with 21 studies of contrast Dobutamine Stress Echo, in all 4 principal planes. The database includes clinical variables, human expert hand-traced myocardial contours and visual scoring. First the problem is studied from a clinical perspective. Quantification of endocardial global and local function using standard measures shows expected values and agreement with human expert visual scoring, but the results are less reliable for myocardial thickening. Next, the problem of segmenting the endocardium with a computer is posed in a standard landmark and atlas-based deformable template model framework. The underlying assumption is that these models can emulate human experts in terms of integrating previous knowledge about the anatomy and physiology with three sources of information from the image: texture, geometry and kinetics. Probabilistic atlases of contrast echocardiography are computed, while noting from histograms at selected anatomical locations that modelling texture with just mean intensity values may be too naive. Intensity analysis together with the clinical results above suggest that lack of external boundary definition may preclude this imaging technique for appropriate measuring of myocardial thickening, while endocardial boundary definition is appropriate for evaluation of wall motion. Geometry is presented in a Principal Component Analysis (PCA) context, highlighting issues about Gaussianity, the correlation and covariance matrices with respect to physiology, and analysing different measures of dimensionality. A popular extension of deformable models ---Active Appearance Models (AAMs)--- is then studied in depth. Contrary to common wisdom, it is contended that using a PCA texture space instead of a fixed atlas is detrimental to segmentation, and that PCA models are not convenient for texture modelling. To integrate kinetics, a novel spatio-temporal model of cardiac contours is proposed. The new explicit model does not require frame interpolation, and it is compared to previous implicit models in terms of approximation error when the shape vector changes from frame to frame or remains constant throughout the cardiac cycle. Finally, the 2D+t atlas-based deformable model segmentation problem is formulated and solved with a gradient descent approach. Experiments using the similarity transformation suggest that segmentation of the whole cardiac volume outperforms segmentation of individual frames. A relatively new approach ---the inverse compositional algorithm--- is shown to decrease running times of the classic Lucas-Kanade algorithm by a factor of 20 to 25, to values that are within real-time processing reach.

Styles APA, Harvard, Vancouver, ISO, etc.

28

Liu, Lanfa, Manfred Buchroithner, Min Ji, Yunyun Dong et Rongchung Zhang. « Quantitative Retrieval of Organic Soil Properties from Visible Near-Infrared Shortwave Infrared (Vis-NIR-SWIR) Spectroscopy Using Fractal-Based Feature Extraction ». Molecular Diversity Preservation International (MDPI), 2016. https://tud.qucosa.de/id/qucosa%3A30203.

Texte intégral

Résumé :

Visible and near-infrared diffuse reflectance spectroscopy has been demonstrated to be a fast and cheap tool for estimating a large number of chemical and physical soil properties, and effective features extracted from spectra are crucial to correlating with these properties. We adopt a novel methodology for feature extraction of soil spectroscopy based on fractal geometry. The spectrum can be divided into multiple segments with different step–window pairs. For each segmented spectral curve, the fractal dimension value was calculated using variation estimators with power indices 0.5, 1.0 and 2.0. Thus, the fractal feature can be generated by multiplying the fractal dimension value with spectral energy. To assess and compare the performance of new generated features, we took advantage of organic soil samples from the large-scale European Land Use/Land Cover Area Frame Survey (LUCAS). Gradient-boosting regression models built using XGBoost library with soil spectral library were developed to estimate N, pH and soil organic carbon (SOC) contents. Features generated by a variogram estimator performed better than two other estimators and the principal component analysis (PCA). The estimation results for SOC were coefficient of determination (R2) = 0.85, root mean square error (RMSE) = 56.7 g/kg, the ratio of percent deviation (RPD) = 2.59; for pH: R2 = 0.82, RMSE = 0.49 g/kg, RPD = 2.31; and for N: R2 = 0.77, RMSE = 3.01 g/kg, RPD = 2.09. Even better results could be achieved when fractal features were combined with PCA components. Fractal features generated by the proposed method can improve estimation accuracies of soil properties and simultaneously maintain the original spectral curve shape.

Styles APA, Harvard, Vancouver, ISO, etc.

29

Elahi, Behin. « Integrated Optimization Models and Strategies for Green Supply Chain Planning ». University of Toledo / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1467266039.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

30

Huang, Po-Han, et 黃柏翰. « Automated Mesh Generation based on Intensity Gradient for 3D Facial Model Reconstruction ». Thesis, 2002. http://ndltd.ncl.edu.tw/handle/9889s3.

Texte intégral

Résumé :

碩士
國立成功大學
醫學工程研究所碩博士班
90
It is important to have a good 3D human face model in plastic surgery simulation. The surgery simulation can be applied on cranial-facial disease or malocclusion. Real-time and accuracy are important goals in developing surgery simulation system. To reduce data set and to build a finite element model can achieve these goals. Shape from shading is cheaper and safer above the methods of reconstruct 3D human face data. At the beginning shape from shading acquire the image of the object from several light source positions. Next we reconstruct the object’s 3D image from the 2D pictures according the illumination gradient of the pictures. The method of shape from shading proposed by Lee and Kuo has the characteristic of high accuracy but high computation time and huge storage data set. To improve the triangular mesh model in their method can solve the problem. Our research firstly acquires the face image from four different light source positions. After applying the Otsu’s thresholding method, we continuum the four images to find out the region of interest. Next we average the images of the four pictures; we can get the image that is approximately light source in the central. After smoothing the image, we can set the image into 3 areas based on illumination gradient initially. Then we apply morphological operator to deal with these 3 areas. After this, we determine the nodes distribution density and distribute grid nodes based on the illumination gradient of each area. Next we use Delaunay triangulation to get the mesh of human face.

Styles APA, Harvard, Vancouver, ISO, etc.

31

Huang, Yan-chi, et 黃彥淇. « Color-based and Gradient-based Object Tracking Using Particle Filter Embedded in Incremental Discriminant Model ». Thesis, 2008. http://ndltd.ncl.edu.tw/handle/56651007620091578478.

Texte intégral

Résumé :

碩士
國立成功大學
資訊工程學系碩博士班
96
This paper presents a multi-feature integrated algorithm which incorporates the particle filter and Fisher linear discriminant (FLD) model for object tracking. To solve the drift problem, the discriminant model for each feature is built up by considering background information to separate the object from background clutter. Similar to Adaboost method, each feature’s reliability is determined by the proposed measuring method, which is used for successive calculation of observation probability in a particle filter. Moreover, to address the object appearance variations and background changes, the FLD model for each feature is renewed by data which is selected according to the co-training concept. Experimental results showed the proposed multi-feature integrated algorithm is able to handle object appearance variations including out-of-plane rotation, partial occlusions, varying illuminations, and scale or viewpoint changes.

Styles APA, Harvard, Vancouver, ISO, etc.

32

Chuang, Ming-Chieh, et 莊明介. « Parameter Identification for Off-line Model Fitting and On-line Model Updating Using Gradient-based Methods ». Thesis, 2017. http://ndltd.ncl.edu.tw/handle/z7b2km.

Texte intégral

Résumé :

博士
國立臺灣大學
土木工程學研究所
105
In the nonlinear structural response simulations, researchers often need to calibrate the parameters of a nonlinear material model with the experimental data by using the trial and error method. This can be very tedious and time consuming. In order to improve the calibration efficiency, the efficient method of parameter identification is desired. This study is to present two gradient-based parameter identification methods (GBM_MF and GBM_MU) for off-line model fitting and on-line model updating, respectively. The proposed GBM_MF method for off-line model fitting can assist the engineers and researchers, who are engaged in the nonlinear structural analyses, in model calibration. In addition, for the advanced hybrid simulation with on-line model updating, the proposed parameter identification method (GBM_MU) with innovative modification is presented in this dissertation. The shaking table test of a five-story BRB frame (BRBF) conducted in E-defense Japan in 2009 is utilized to verify the effectiveness of the proposed methods in the off-line and on-line applications. Compared with the measured responses, the results of off-line model fitting application can confirm that the proposed gradient-based method (GBM_MF) allows the efficient model calibration for the accurate simulation of the nonlinear responses of the BRBF. Moreover, the advantage of the on-line model updating with the proposed parameter identification method (GBM_MU) is demonstrated through the simulated hybrid tests. As a result, the proposed gradient-based methods of parameter identification for off-line model fitting and on-line model updating can advance the earthquake engineering research and practice.

Styles APA, Harvard, Vancouver, ISO, etc.

33

Lin, Yi-Chun, et 林以淳. « Strain Field Determination Based on Displacement Gradient Model and Unified Least-Squares Technique ». Thesis, 2014. http://ndltd.ncl.edu.tw/handle/72505607860055099000.

Texte intégral

Résumé :

碩士
國立臺灣大學
土木工程學研究所
102
Deformation analysis is crucial to applications of structural engineering, geodesy and geology, of which the main goal is to detect behaviors of a deformed body. At present most deformation analysis relies on a limited number of high accuracy observations. However, it is insufficient when it comes to describing the strain field on the entire object. Modern techniques, including digital photogrammetry and the Light Detection and Ranging (LiDAR), provide the possibility to obtain a large number of observations in a very efficient manner. These large amount of data can be used to better estimate strain field with appropriate analyzing methods. In this study, a method based on displacement gradient model and unified least-squares is proposed to improve classical deformation analysis; in addition, the corresponding quality assessment and sensitivity analysis are derived accordingly. Furthermore, using a nearest neighboring searching and triangulated irregular network, a strategy for analyzing vast number of observations is established. Numerical experiments based on both simulated and real data suggested that the proposed approach processed large data to detected behaviors of a deformed body in an effective and efficient way.

Styles APA, Harvard, Vancouver, ISO, etc.

34

Svoboda, Pavel. « Rozšíření, diverzita a ekologie bentických krásivek na lokálním prostorovém měřítku ». Master's thesis, 2012. http://www.nusl.cz/ntk/nusl-309662.

Texte intégral

Résumé :

Besides spatial heterogeneity, an important component of diversity of the protist communities is also the variation in species assemblages through time (temporal turnover). Spatial and temporal variation in patterns of distribution and abundance of lentic microphytobenthos assemblages is often large and occurs at relatively small spatial scale. Desmids (Zygnematophyceae) often constitute a characteristic part of the microphytobenthos of peat bogs. Despite their important role in primary production and fact that they are useful indicators of ecosystem uniqueness, investigations of their seasonality and spatial distribution are scarce. In my thesis I have investigated if desmid epipelic communities are driven rather by neutral or niche-based processes, and I also focused on the factors affecting their diversity, seasonal dynamics and spatial patterns at the local spatial scale. The study was conducted at the two different types of biotopes - minerotrophic lowland peat bogs (Doksy region) and ombrotrophic raised bogs (Jizera Mountains region). Seasonal changes in species composition and diversity of assemblages were not evident. This may be affected by a monopolization effect and also that local abundance of species was positively correlated with population persistence, which suggests that high local...

Styles APA, Harvard, Vancouver, ISO, etc.

35

Cabrita, Cristiano Lourenço. « Design of neuro-fuzzy models by evolutionary and gradient-based algorithms ». Doctoral thesis, 2013. http://hdl.handle.net/10400.1/6100.

Texte intégral

Résumé :

All systems found in nature exhibit, with different degrees, a nonlinear behavior. To emulate this behavior, classical systems identification techniques use, typically, linear models, for mathematical simplicity. Models inspired by biological principles (artificial neural networks) and linguistically motivated (fuzzy systems), due to their universal approximation property, are becoming alternatives to classical mathematical models. In systems identification, the design of this type of models is an iterative process, requiring, among other steps, the need to identify the model structure, as well as the estimation of the model parameters. This thesis addresses the applicability of gradient-basis algorithms for the parameter estimation phase, and the use of evolutionary algorithms for model structure selection, for the design of neuro-fuzzy systems, i.e., models that offer the transparency property found in fuzzy systems, but use, for their design, algorithms introduced in the context of neural networks. A new methodology, based on the minimization of the integral of the error, and exploiting the parameter separability property typically found in neuro-fuzzy systems, is proposed for parameter estimation. A recent evolutionary technique (bacterial algorithms), based on the natural phenomenon of microbial evolution, is combined with genetic programming, and the resulting algorithm, bacterial programming, advocated for structure determination. Different versions of this evolutionary technique are combined with gradient-based algorithms, solving problems found in fuzzy and neuro-fuzzy design, namely incorporation of a-priori knowledge, gradient algorithms initialization and model complexity reduction.
Todos os sistemas encontrados na natureza exibem, com maior ou menor grau, um comportamento linear. De modo a emular esse comportamento, as técnicas de identificação clássicas usam, tipicamente e por simplicidade matemática, modelos lineares. Devido à sua propriedade de aproximação universal, modelos inspirados por princípios biológicos (redes neuronais artificiais) e motivados linguisticamente (sistemas difusos) tem sido cada vez mais usados como alternativos aos modelos matemáticos clássicos. Num contexto de identificação de sistemas, o projeto de modelos como os acima descritos é um processo iterativo, constituído por vários passos. Dentro destes, encontra-se a necessidade de identificar a estrutura do modelo a usar, e a estimação dos seus parâmetros. Esta Tese discutirá a aplicação de algoritmos baseados em derivadas para a fase de estimação de parâmetros, e o uso de algoritmos baseados na teoria da evolução de espécies, algoritmos evolutivos, para a seleção de estrutura do modelo. Isto será realizado no contexto do projeto de modelos neuro-difusos, isto é, modelos que simultaneamente exibem a propriedade de transparência normalmente associada a sistemas difusos mas que utilizam, para o seu projeto algoritmos introduzidos no contexto de redes neuronais. Os modelos utilizados neste trabalho são redes B-Spline, de Função de Base Radial, e sistemas difusos dos tipos Mamdani e Takagi-Sugeno. Neste trabalho começa-se por explorar, para desenho de redes B-Spline, a introdução de conhecimento à-priori existente sobre um processo. Neste sentido, aplica-se uma nova abordagem na qual a técnica para a estimação dos parâmetros é alterada a fim de assegurar restrições de igualdade da função e das suas derivadas. Mostra-se ainda que estratégias de determinação de estrutura do modelo, baseadas em computação evolutiva ou em heurísticas determinísticas podem ser facilmente adaptadas a este tipo de modelos restringidos. É proposta uma nova técnica evolutiva, resultante da combinação de algoritmos recentemente introduzidos (algoritmos bacterianos, baseados no fenómeno natural de evolução microbiana) e programação genética. Nesta nova abordagem, designada por programação bacteriana, os operadores genéticos são substituídos pelos operadores bacterianos. Deste modo, enquanto a mutação bacteriana trabalha num indivíduo, e tenta otimizar a bactéria que o codifica, a transferência de gene é aplicada a toda a população de bactérias, evitando-se soluções de mínimos locais. Esta heurística foi aplicada para o desenho de redes B-Spline. O desempenho desta abordagem é ilustrada e comparada com alternativas existentes. Para a determinação dos parâmetros de um modelo são normalmente usadas técnicas de otimização locais, baseadas em derivadas. Como o modelo em questão é não-linear, o desempenho deste género de técnicas é influenciado pelos pontos de partida. Para resolver este problema, é proposto um novo método no qual é usado o algoritmo evolutivo referido anteriormente para determinar pontos de partida mais apropriados para o algoritmo baseado em derivadas. Deste modo, é aumentada a possibilidade de se encontrar um mínimo global. A complexidade dos modelos neuro-difusos (e difusos) aumenta exponencialmente com a dimensão do problema. De modo a minorar este problema, é proposta uma nova abordagem de particionamento do espaço de entrada, que é uma extensão das estratégias de decomposição de entrada normalmente usadas para este tipo de modelos. Simulações mostram que, usando esta abordagem, se pode manter a capacidade de generalização com modelos de menor complexidade. Os modelos B-Spline são funcionalmente equivalentes a modelos difusos, desde que certas condições sejam satisfeitas. Para os casos em que tal não acontece (modelos difusos Mamdani genéricos), procedeu-se à adaptação das técnicas anteriormente empregues para as redes B-Spline. Por um lado, o algoritmo Levenberg-Marquardt é adaptado e a fim de poder ser aplicado ao particionamento do espaço de entrada de sistema difuso. Por outro lado, os algoritmos evolutivos de base bacteriana são adaptados para sistemas difusos, e combinados com o algoritmo de Levenberg-Marquardt, onde se explora a fusão das características de cada metodologia. Esta hibridização dos dois algoritmos, denominada de algoritmo bacteriano memético, demonstrou, em vários problemas de teste, apresentar melhores resultados que alternativas conhecidas. Os parâmetros dos modelos neuronais utilizados e dos difusos acima descritos (satisfazendo no entanto alguns critérios) podem ser separados, de acordo com a sua influência na saída, em parâmetros lineares e não-lineares. Utilizando as consequências desta propriedade nos algoritmos de estimação de parâmetros, esta Tese propõe também uma nova metodologia para estimação de parâmetros, baseada na minimização do integral do erro, em alternativa à normalmente utilizada minimização da soma do quadrado dos erros. Esta técnica, além de possibilitar (em certos casos) um projeto totalmente analítico, obtém melhores resultados de generalização, dado usar uma superfície de desempenho mais similar aquela que se obteria se se utilizasse a função geradora dos dados.

Styles APA, Harvard, Vancouver, ISO, etc.

36

Hu, Richard Zhi Ling. « Vision-Based Observation Models for Lower Limb 3D Tracking with a Moving Platform ». Thesis, 2011. http://hdl.handle.net/10012/6110.

Texte intégral

Résumé :

Tracking and understanding human gait is an important step towards improving elderly mobility and safety. This thesis presents a vision-based tracking system that estimates the 3D pose of a wheeled walker user's lower limbs with cameras mounted on the moving walker. The tracker estimates 3D poses from images of the lower limbs in the coronal plane in a dynamic, uncontrolled environment. It employs a probabilistic approach based on particle filtering with three different camera setups: a monocular RGB camera, binocular RGB cameras, and a depth camera. For the RGB cameras, observation likelihoods are designed to compare the colors and gradients of each frame with initial templates that are manually extracted. Two strategies are also investigated for handling appearance change of tracking target: increasing number of templates and using different representations of colors. For the depth camera, two observation likelihoods are developed: the first one works directly in the 3D space, while the second one works in the projected image space. Experiments are conducted to evaluate the performance of the tracking system with different users for all three camera setups. It is demonstrated that the trackers with the RGB cameras produce results with higher error as compared to the depth camera, and the strategies for handling appearance change improve tracking accuracy in general. On the other hand, the tracker with the depth sensor successfully tracks the 3D poses of users over the entire video sequence and is robust against unfavorable conditions such as partial occlusion, missing observations, and deformable tracking target.

Styles APA, Harvard, Vancouver, ISO, etc.

37

Scellier, Benjamin. « A deep learning theory for neural networks grounded in physics ». Thesis, 2020. http://hdl.handle.net/1866/25593.

Texte intégral

Résumé :

Au cours de la dernière décennie, l'apprentissage profond est devenu une composante majeure de l'intelligence artificielle, ayant mené à une série d'avancées capitales dans une variété de domaines. L'un des piliers de l'apprentissage profond est l'optimisation de fonction de coût par l'algorithme du gradient stochastique (SGD). Traditionnellement en apprentissage profond, les réseaux de neurones sont des fonctions mathématiques différentiables, et les gradients requis pour l'algorithme SGD sont calculés par rétropropagation. Cependant, les architectures informatiques sur lesquelles ces réseaux de neurones sont implémentés et entraînés souffrent d’inefficacités en vitesse et en énergie, dues à la séparation de la mémoire et des calculs dans ces architectures. Pour résoudre ces problèmes, le neuromorphique vise à implementer les réseaux de neurones dans des architectures qui fusionnent mémoire et calculs, imitant plus fidèlement le cerveau. Dans cette thèse, nous soutenons que pour construire efficacement des réseaux de neurones dans des architectures neuromorphiques, il est nécessaire de repenser les algorithmes pour les implémenter et les entraîner. Nous présentons un cadre mathématique alternative, compatible lui aussi avec l’algorithme SGD, qui permet de concevoir des réseaux de neurones dans des substrats qui exploitent mieux les lois de la physique. Notre cadre mathématique s'applique à une très large classe de modèles, à savoir les systèmes dont l'état ou la dynamique sont décrits par des équations variationnelles. La procédure pour calculer les gradients de la fonction de coût dans de tels systèmes (qui dans de nombreux cas pratiques ne nécessite que de l'information locale pour chaque paramètre) est appelée “equilibrium propagation” (EqProp). Comme beaucoup de systèmes en physique et en ingénierie peuvent être décrits par des principes variationnels, notre cadre mathématique peut potentiellement s'appliquer à une grande variété de systèmes physiques, dont les applications vont au delà du neuromorphique et touchent divers champs d'ingénierie.
In the last decade, deep learning has become a major component of artificial intelligence, leading to a series of breakthroughs across a wide variety of domains. The workhorse of deep learning is the optimization of loss functions by stochastic gradient descent (SGD). Traditionally in deep learning, neural networks are differentiable mathematical functions, and the loss gradients required for SGD are computed with the backpropagation algorithm. However, the computer architectures on which these neural networks are implemented and trained suffer from speed and energy inefficiency issues, due to the separation of memory and processing in these architectures. To solve these problems, the field of neuromorphic computing aims at implementing neural networks on hardware architectures that merge memory and processing, just like brains do. In this thesis, we argue that building large, fast and efficient neural networks on neuromorphic architectures also requires rethinking the algorithms to implement and train them. We present an alternative mathematical framework, also compatible with SGD, which offers the possibility to design neural networks in substrates that directly exploit the laws of physics. Our framework applies to a very broad class of models, namely those whose state or dynamics are described by variational equations. This includes physical systems whose equilibrium state minimizes an energy function, and physical systems whose trajectory minimizes an action functional (principle of least action). We present a simple procedure to compute the loss gradients in such systems, called equilibrium propagation (EqProp), which requires solely locally available information for each trainable parameter. Since many models in physics and engineering can be described by variational principles, our framework has the potential to be applied to a broad variety of physical systems, whose applications extend to various fields of engineering, beyond neuromorphic computing.

Styles APA, Harvard, Vancouver, ISO, etc.

38

He, Jin. « Urban Detection From Hyperspectral Images Using Dimension-Reduction Model and Fusion of Multiple Segmentations Based on Stuctural and Textural Features ». Thèse, 2013. http://hdl.handle.net/1866/10281.

Texte intégral

Résumé :

Ce mémoire de maîtrise présente une nouvelle approche non supervisée pour détecter et segmenter les régions urbaines dans les images hyperspectrales. La méthode proposée n ́ecessite trois étapes. Tout d’abord, afin de réduire le coût calculatoire de notre algorithme, une image couleur du contenu spectral est estimée. A cette fin, une étape de réduction de dimensionalité non-linéaire, basée sur deux critères complémentaires mais contradictoires de bonne visualisation; à savoir la précision et le contraste, est réalisée pour l’affichage couleur de chaque image hyperspectrale. Ensuite, pour discriminer les régions urbaines des régions non urbaines, la seconde étape consiste à extraire quelques caractéristiques discriminantes (et complémentaires) sur cette image hyperspectrale couleur. A cette fin, nous avons extrait une série de paramètres discriminants pour décrire les caractéristiques d’une zone urbaine, principalement composée d’objets manufacturés de formes simples g ́eométriques et régulières. Nous avons utilisé des caractéristiques texturales basées sur les niveaux de gris, la magnitude du gradient ou des paramètres issus de la matrice de co-occurrence combinés avec des caractéristiques structurelles basées sur l’orientation locale du gradient de l’image et la détection locale de segments de droites. Afin de réduire encore la complexité de calcul de notre approche et éviter le problème de la ”malédiction de la dimensionnalité” quand on décide de regrouper des données de dimensions élevées, nous avons décidé de classifier individuellement, dans la dernière étape, chaque caractéristique texturale ou structurelle avec une simple procédure de K-moyennes et ensuite de combiner ces segmentations grossières, obtenues à faible coût, avec un modèle efficace de fusion de cartes de segmentations. Les expérimentations données dans ce rapport montrent que cette stratégie est efficace visuellement et se compare favorablement aux autres méthodes de détection et segmentation de zones urbaines à partir d’images hyperspectrales.
This master’s thesis presents a new approach to urban area detection and segmentation in hyperspectral images. The proposed method relies on a three-step procedure. First, in order to decrease the computational complexity, an informative three-colour composite image, minimizing as much as possible the loss of information of the spectral content, is computed. To this end, a non-linear dimensionality reduction step, based on two complementary but contradictory criteria of good visualization, namely accuracy and contrast, is achieved for the colour display of each hyperspectral image. In order to discriminate between urban and non-urban areas, the second step consists of extracting some complementary and discriminant features on the resulting (three-band) colour hyperspectral image. To attain this goal, we have extracted a set of features relevant to the description of different aspects of urban areas, which are mainly composed of man-made objects with regular or simple geometrical shapes. We have used simple textural features based on grey-levels, gradient magnitude or grey-level co-occurence matrix statistical parameters combined with structural features based on gradient orientation, and straight segment detection. In order to also reduce the computational complexity and to avoid the so-called “curse of dimensionality” when clustering high-dimensional data, we decided, in the final third step, to classify each individual feature (by a simple K-means clustering procedure) and to combine these multiple low-cost and rough image segmentation results with an efficient fusion model of segmentation maps. The experiments reported in this report demonstrate that the proposed segmentation method is efficient in terms of visual evaluation and performs well compared to existing and automatic detection and segmentation methods of urban areas from hyperspectral images.

Styles APA, Harvard, Vancouver, ISO, etc.

Thèses sur le sujet « Gradient-based model »

Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres