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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Utilisation de prédicteurs sinusoïdaux pour la simulation temporelle de systèmes électriques en courant alternatif / Use of sinusoidal predictors for time domain simulation of AC power systems

Gibert, Pierre-Marie 30 November 2018 (has links)
Simuler temporellement les réseaux électriques modernes requiert d'importants moyens de calcul de par la dimension et la raideur des systèmes différentiels algébriques résultants. De plus, la fréquence d'oscillation de certains signaux simulés contraint fortement le pas d'intégration des schémas classiques, y compris en régime établi où ils sont proches de sinusoïdes oscillant à la fréquence nominale du système. L'objectif de la méthode des prédicteurs sinusoïdaux proposée dans cette thèse est donc de tirer parti de cette propriété afin d'améliorer les performances du solveur tout en contrôlant l'erreur de calcul. Elle consiste à décomposer la solution en deux parties : une sinusoïde, dont les coefficients de Fourier sont fixés pour chaque intervalle d'intégration puis mis à jour par estimation paramétrique, et un terme de correction sur lequel le système d'EDA est reformulé et résolu à l'aide d'un schéma d'intégration à pas adaptatif. Une attention particulière a été portée au choix de l'estimateur paramétrique, ce dernier ayant un impact direct sur le pas d'intégration de par sa précision et indirect de par son effet sur la stabilité globale de la méthode. L'estimateur finalement développé consiste à calculer les coefficients de Fourier qui minimisent une mesure de la stationnarité du système. Ce dernier étant convergent en régime permanent, le terme de correction est progressivement amorti, permettant ainsi d'accroître considérablement le pas d'intégration. Cette méthode, intégrée au sein du solveur SUNDIALS IDA puis interfacée avec un moteur de calcul industriel, permet d'accélérer très nettement les simulations en comparaison avec une implémentation classique / Modern power systems time-domain simulations require important computational resources due to the resulting differential algebraic systems dimension and stiffness. In addition, some simulated signals oscillation frequency dramatically limits the classical schemes step size, even in steady-state during which they are close to sinusoids oscillating at system nominal frequency. That's why the sinusoidal predictors method proposed in this thesis aims at taking this property into account in order to enhance solver performances while controlling the integration error. It consists in decomposing the solution into two parts: a sinusoid, whose Fourier coefficients are fixed for each time integration interval and then updated by parametric estimation, and a correction term on which the DAE system is rewritten and solved using an adaptive step size integration scheme. A particular focus has been given on the estimator choice, given its precision direct impact on the step size and its indirect effect on the global method stability. The finally developed estimator consists in computing Fourier coefficients minimizing a system stationarity measurement. As it converges in steady-state, the correction term is progressively damped, which enables to considerably increase the step size. This method, integrated into the reference solver SUNDIALS IDA and interfaced with an industrial simulation engine, enables to very significantly accelerate simulations in comparison with a classical implementation
22

Etude et réduction d'ordre de modèles linéraires structurés : application à la dynamique du véhicule / Study and order reduction of linear structured models : application to vehicle dynamics

Guillet, Jérôme 27 October 2011 (has links)
Cette thèse traite de modélisation des systèmes complexes. Dans ce cadre, l'approche est basée sur les Modèles Structurés en Second Ordre (MSSO). Afin d'utiliser cette classe de modèles, les propriétés telles que l'atteignabilité, l'observabilité et les grammiens, bien connues pour les réalisations d'états, sont étendues aux MSSO.Lors de la co-simulation d'un système, des éléments de natures différentes (physiques et logicielles) sont intégrés et la simulation est effectuée en temps réel. Or, les modèles d'ordre élevés sont couteux en temps de calcul, ce qui rend difficile ce type de simulation. Ainsi, des méthodes de réduction de modèle sont explorées. En particulier, de nouvelles méthodes, permettant de préserver la structure des modèles avec une bonne erreur d'approximation sont présentées.Ces développements sont appliqués à la co-simulation de modèles véhicules sous forme de MSSO. Le modèle créé est un modèle par blocs, complexe et non-linéaire. Afin d'appliquer les méthodes de réduction de modèle il est nécessaire de le linéariser. La structure par blocs permet de linéariser l'ensemble du modèle ou de ne linéariser que certaines sous parties du modèle.Ensuite, l'identification des paramètres est effectuée pour chaque sous-systèmes du véhicule. Une méthode d'interconnexion est ensuite proposée pour créer une représentation monobloc du modèle afin de réduire ce dernier. Au final, des essais en co-simulation de la partie arrière du véhicule sous forme de modèle interconnectée avec la partie avant du véhicule physiquement présente sur un banc de test, valide notre approche pour effectuer de la co-simulation temps réel avec matériel.x / This thesis studies the modeling of complex systems. In this framework, the approach is based on Second Order Form Model (SOFM). In order to use this kind of models, properties such as the reachability, the observability, the gramians and the Markov parameters, well known for state-space representation, are extended to the SOFM. During the co-simulation of a system, its physical parts are interconnected to models which simulate the system environement and the simulation is performed in real time. However, the simulation of high order models consumes to much time to be performed in real time. Therefore, model order reduction methods are studied. Particularly, new methods preserving SOFM structure with a good approximation error are presented. These developments are applied to the vehicle dynamic. Hence, a vehicle SOFM model is developed. The created model is a blockwise model where each blocks describes a part of the vehicle. This model is complex and non-linear. In order to apply the model order reduction methods, model linearisation is necessary. The block modeling allows to linearise the full model or allows to linearise some part of the model. Then, the identification of the model parameters is done by vehicle sub-system. In addition, an interconnection method is proposed to build a monobloc model in order to reduce it. Finally, co-simulations of the model vehicle rear part interconnected to the physical front part of the vehicle show the capacity to make co-simulation with the reduced models.
23

Modeling And Simulation Of A Maneuvering Ship

Pakkan, Sinan 01 October 2007 (has links) (PDF)
This thesis documents the studies conducted in deriving a mathematical model representing the dynamics of a maneuvering ship to be implemented as part of an interactive real-time simulation system, as well as the details and results of the implementation process itself. Different effects on the dynamics of ship motions are discussed separately, meaning that the effects are considered to be applied to the system one at a time and they are included in the model simply by the principle of superposition. The model is intended to include the hydrodynamic interactions between the ship hull and the ocean via added mass (added inertia), damping and restoring force concepts. In addition to these effects, which are derived considering no incident waves are present on the ocean, the environmental disturbances, such as wind, wave and ocean current are also taken into account for proposing a mathematical model governing the dynamics of the ship. Since the ultimate product of this thesis work is a running computer code that can be integrated into an available simulation software, the algorithm development and code implementation processes are also covered. Improvements made on the implementation to achieve &ldquo / better&rdquo / real-time performance are evaluated comparatively in reference to original runs conducted before the application of improvement under consideration. A new method to the computation of the wave model that allows faster calculation in real-time is presented. A modular programming approach is followed in the overall algorithm development process in order to make the integration of new program components into the software, such as a new hull or propulsion model or a different integrator type possible, easily and quickly.
24

Development of an optimisation approach to Alamouti 4×2 space time block coding firmware.

Kambale, Witesyavwirwa Vianney. January 2014 (has links)
M. Tech. Electrical Engineering. / Discusses MIMO systems have been hailed for the benefits of enhancing the reliability of the wireless communication link and increasing of the channel capacity, however the complexity of MIMO encoding and decoding algorithms increases considerably with the number of antennas. This research aims to suggest an optimisation approach to a reduced complexity implementation of the Alamouti 4×2 STBC. This is achieved by considering the FPGA parallelisation of the conditionally optimised ML decoding algorithm. The above problem can be divided into two subproblems. 1. The ML decoding of the Double Alamouti 4×2 STBC has a high computational cost when an exhaustive search is performed on the signal constellation for M-ary QAM. 2. Though the conditionally optimised ML decoding leads to less computational complexity compared to the full generic ML detection algorithm, the practical implementation remains unattractive for wireless systems.
25

Automated Planning and Scheduling for Industrial Construction Processes

Hu, Di Unknown Date
No description available.
26

[en] A NEW APPROACH TO GENERATE TIME SERIES PERIODICAL SCENARIOS VIA NON-LINEAR MODELS / [pt] UMA NOVA ABORDAGEM PARA GERAÇÃO DE CENÁRIOS DE SÉRIES TEMPORAIS PERIÓDICAS VIA MODELOS NÃO LINEARES

VICTOR EDUARDO LEITE DE A DUCA 23 March 2018 (has links)
[pt] Os modelos autorregressivos são comumente encontrados dentro do contexto de séries hidrológicas, especificamente em séries de vazões e/ou ENA (Energia Natural Afluente). Muitos destes modelos são de ordem 1, possuem parâmetros constantes ou periódicos e necessitam do requisito de normalidade. Segundo a literatura, séries de vazões anuais podem ser aproximadas para distribuições normais, porém em períodos de tempo curtos como diário, semanal e mensal esta característica não é observada, especialmente pelo problema de assimetria. Devido a isto, uma nova classe de modelo de ordem 1 foi estudada na tentativa de suprir tal problema. O novo modelo mantém estrutura autorregressiva, pode ser aditivo, multiplicativo ou híbrido, onde incorpora propriedades aditivas e multiplicativas conjunta- mente, porém suas marginais assumirão distribuição gama. Além disso, a modelagem parte do pressuposto que os Métodos de Momentos são eficientes para estimação de seus parâmetros. Recentemente esta abordagem, sob a forma híbrida, não demonstrou sucesso para o contexto do despacho hidrotérmico brasileiro. O presente trabalho foca na análise completa do modelo híbrido para as séries do Setor Elétrico Brasileiro, trazendo como novidade a estimação via máxima verossimilhança além dos estudos isolados de modelos aditivos e multiplicativos. Os resultados revelaram uma linha de pesquisa promissora, abrindo um campo de possibilidades para que novas ordens superiores a primeira ou distribuições assimétricas possam ser estudadas partindo deste princípio. / [en] Autoregressive models are commonly found in the context of hydrological series, specifically in streamflow and/or ANE series (Affluent Natural Energy). Most of them are models of order 1, which have constant or periodic parameters and need the requirement of normality. According to the literature, annual streamflow series can be approximated for normal distributions, however, in short periods of time, like daily, weekly and monthly, this feature is not observed, especially because of the asymmetry issue. Due to this reason, a new class of model of order 1 was studied for attempting to solve such problem. The new model keeps autoregressive structure and can be additive, multiplicative or hybrid, in which embodies additive and multiplicative properties together, but its marginals will assume gamma distribution. Moreover, this modeling departs from the presupposition that Methods of Moments are efficient to the estimation of its parameters. Recently, this approach, under the hybrid way, has not proved to be successful to the context of Brazilian hydrothermal dispatch. This work focuses on the complete analysis of hybrid model to the series of the Brazilian Electric Sector, bringing, as novelty, Maximum Likelihood Estimation, besides isolated studies of additive and multiplicative models. The results revealed a prosperous line of research, opening a field of possibilities for new orders or asymmetric distributions to be studied starting from this point.
27

Sistemas complexos, séries temporais e previsibilidade / Complex systems, time series and predictability

Henrique Carli 04 February 2011 (has links)
Para qualquer sistema observado, físico ou qualquer outro, geralmente se deseja fazer predições para sua evolução futura. Algumas vezes, muito pouco é conhecido sobre o sistema. Se uma série temporal é a única fonte de informação no sistema, predições de valores futuros da série requer uma modelagem da lei da dinâmica do sistema, talvez não linear. Um interesse em particular são as capacidades de previsão do modelo global para análises de séries temporais. Isso pode ser um procedimento muito complexo e computacionalmente muito alto. Nesta dissertação, nos concetraremos em um determinado caso: Em algumas situações, a única informação que se tem sobre o sistema é uma série sequencial de dados (ou série temporal). Supondo que, por detrás de tais dados, exista uma dinâmica de baixa dimensionalidade, existem técnicas para a reconstrução desta dinâmica.O que se busca é desenvolver novas técnicas para poder melhorar o poder de previsão das técnicas já existentes, através da programação computacional em Maple e C/C++.
28

Nova metodologia para a estimativa de capacitância e consumo de potência de portas lógicas complexas CMOS no nível lógico / New methodology to the estimative of capacitance and power consumption of complex logic gates cmos at logic level

Ghissoni, Sidinei 31 October 2005 (has links)
Conselho Nacional de Desenvolvimento Científico e Tecnológico / This dissertation presents a methodology of capacitance estimation and power consumption in CMOS circuits combinational constituted basically of complex logic gates at logic level. The main objective in the development of this method is to provide a fast estimate of the power consumption of circuits at the logical design gates. Of this form, the considered method allows to the application of techniques to the reduction of power consumption or the alteration of the design before being prototyped. The consumed dynamic power in complex logic gates depends on the following factors: switching activity of each circuit node, voltage of supplies, parasite capacitance and clock frequency. With the exception of the parasite capacitance, all other parameters are easily determined. The analysis proposed in this dissertation, treats estimative of the dynamic power consumption of complex logic gates, through the estimate of the parasite capacitance CMOS devices. The model considered here concentrates all internal capacitances on the external gate nodes depending on the combinations of the input signals. The resulting capacitance in an only external node of an input of the gate is resulted of the transitions of inputs of the too much nodes on the node that if wants to determine. The results obtained in this work, regarding the estimate of power consumption of the complex logic gates, had been considered satisfactory, once they had presented a maximum error of 10% when compared with to the electric simulation result preformed with ELDO. Moreover, the method supplies significant reduction in the simulation time of the circuits, being able esteem the power consumption of a circuit up to 200 times faster than gotten to the simulated electric level with ELDO tool. / Este trabalho apresenta uma metodologia de estimativa de capacitâncias e de consumo de potência de circuitos CMOS constituídos basicamente por portas lógicas complexas no nível lógico. O principal objetivo no desenvolvimento deste método é fazer uma rápida previsão do consumo de potência de circuitos ainda na fase de projeto lógico composto de portas complexas. Desta forma, o método proposto permite a aplicação de técnicas de redução de consumo de potência ou a alteração de todo o projeto antes de ser prototipado. A potência dinâmica consumida em portas lógicas complexas depende dos seguintes fatores: atividade de comutação de cada nó do circuito, tensão de alimentação, freqüência de operação e da capacitância parasita. Com a exceção da capacitância parasita, todos os demais parâmetros são facilmente determinados. A análise proposta nesta dissertação, trata da aproximação (cálculo aproximado) do consumo de potência dinâmica de portas lógicas complexas, através da estimativa da capacitância parasita dos dispositivos CMOS. O modelo aqui proposto concentra as capacitâncias nos nós externos das portas, que variam em função das combinações dos sinais de entrada. A capacitância resultante, representada em um único nó externo da entrada da porta analisada, é resultado das transições dos sinais das demais entradas que agem sobre o nó que se quer determinar. Os resultados obtidos neste trabalho a respeito da estimativa de consumo potência das portas lógicas complexas foram considerados satisfatórios, pois apresentaram um erro máximo de 10% quando comparados às simulações elétricas pelo uso da ferramenta ELDO. Além disso, o método fornece significante redução no tempo de simulação dos circuitos, podendo estimar o consumo de potência de um circuito até 200 vezes mais rápido que obtido ao nível elétrico simulado com a ferramenta ELDO.
29

Sistemas complexos, séries temporais e previsibilidade / Complex systems, time series and predictability

Henrique Carli 04 February 2011 (has links)
Para qualquer sistema observado, físico ou qualquer outro, geralmente se deseja fazer predições para sua evolução futura. Algumas vezes, muito pouco é conhecido sobre o sistema. Se uma série temporal é a única fonte de informação no sistema, predições de valores futuros da série requer uma modelagem da lei da dinâmica do sistema, talvez não linear. Um interesse em particular são as capacidades de previsão do modelo global para análises de séries temporais. Isso pode ser um procedimento muito complexo e computacionalmente muito alto. Nesta dissertação, nos concetraremos em um determinado caso: Em algumas situações, a única informação que se tem sobre o sistema é uma série sequencial de dados (ou série temporal). Supondo que, por detrás de tais dados, exista uma dinâmica de baixa dimensionalidade, existem técnicas para a reconstrução desta dinâmica.O que se busca é desenvolver novas técnicas para poder melhorar o poder de previsão das técnicas já existentes, através da programação computacional em Maple e C/C++.
30

Real-Time Fluid Simulation and Visualization / Simulering och visualisering av vätskor i realtid

Wolmerud, Markus January 2015 (has links)
This thesis presents a method based on Smoothed Particle Hydrodynamics to simulate sparse particle systems with fluid like properties in real-time. The simulation supports interactions with terrain and objects and is scaled depending on activity of the fluid. We use a carpet method on the GPU to visualize the water surface with translucency, reflection, refraction and added topology. Splash effects and foam are imitated and added as a last step.

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