Дисертації: "Method of equivalent charges"

1

Susetyo, Budi. "Modélisation de l'impédance harmonique de charges agrégées." Grenoble INPG, 1995. http://www.theses.fr/1995INPG0027.

Повний текст джерела

Анотація:

Les applications de l’électronique de puissance contribuent à la pollution harmonique des réseaux électriques. Pour estimer le niveau de distorsion de tension, les différents composants du réseau doivent être modélisés en régime harmonique, en particulier les charges consommatrices, industrielles, commerciales et domestiques. L’étude concerne la modélisation de l’impédance harmonique des charges qui peuvent être séparées en deux grandes catégories: les charges passives et les charges dites actives qui réalisent une conversion d’énergie électromécanique. Les modèles disponibles pour les charges élémentaires sont récapitules en termes de complexité et de précision. Puis une méthode d’agrégation est développée, permettant d'obtenir un circuit équivalent d'ordre minimal et de structure compatible avec celle du réseau. La méthode d'identification des paramètres de ce circuit est basée sur une représentation fréquentielle de l’impédance harmonique, afin d'obtenir une réponse qui coïncide avec celle du réseau réel. Ce modèle agrège est utilise pour étudier la sensibilité de l’impédance harmonique aux variations aléatoires des paramètres caractéristiques du réseau et des charges.

Стилі APA, Harvard, Vancouver, ISO та ін.

2

Грецких, Светлана Владимировна. "Ослабление статического геомагнитного поля ферромагнитными элементами домов". Thesis, Государственное учреждение "Институт технических проблем магнетизма НАН Украины", 2015. http://repository.kpi.kharkov.ua/handle/KhPI-Press/21435.

Повний текст джерела

Анотація:

Диссертация на соискание ученой степени кандидата технических наук по специальности 05.09.05 – теоретическая электротехника. – Национальный технический университет "Харьковский политехнический институт", Харьков, 2016. Диссертация посвящена математическому моделированию явления ослабления статического геомагнитного поля (ГМП) в помещениях жилых домов и разработке рекомендаций по методам его нормализации до безопасного уровня. Полученные в диссертации результаты в совокупности составляют существенный вклад в решение научно-прикладной задачи теоретической электротехники по моделированию явления ослабления ГМП стальными ферромагнитными элементами конструкций домов и разработки рекомендаций по методам нормализации ГМП в помещениях до безопасного для людей уровня. Основные результаты выполненных в диссертации исследований и практических разработок использованы при выполнении тематического плана ГУ "ИТПМ НАН Украины", в Институте гигиены и медицинской экологии им. А. Н. Марзеева НАМН Украины при разработке "Государственных санитарных правил и норм защиты населения от влияния электромагнитных излучений", при проектировании и строительстве в г. Харькове современных каркасно-монолитных жилых домов с безопасными условиями проживания (ООО "АВУАР"). Результаты работы рекомендованы к применению научным и промышленным учреждениям и предприятиям, выполняющим разработку методов и средств моделирования, расчета и нормализации статического ГМП в жилых домах, проектирующим современные жилые дома с безопасными условиями проживания по магнитному полю.
Thesis for scientific degree of candidate of technical sciences, specialty 05.09.05 – theoretical electrical engineering. – National Technical University "Kharkiv Polytechnic Institute", Kharkiv, 2016. The thesis is devoted to mathematical modeling of the phenomenon of weakening of the static geomagnetic field (GMF) in residential homes and to the development of recommendations on how to normalize it to a safe level. The modeling of weakening of the GMF was performed with the help of the equivalent charges method. The cylindrical ferromagnetic column was taken as an example. In the framework of this technique the problem of calculation of the GMF’s induction weakened by extended ferromagnetic elements was solved. The physical parameters of the ferromagnetic column which effect the weakening of GMF are determined. The conditions under which GMF is reduced to the safety level are also determined. This is due to the changes of the GMF’s geometry and reducing of initial magnetic permeability of its material. The Arcadiev method of the effective magnetic permeability for modeling of magneticfield of reinforced concrete columns and intermediate floors was developed. The numerical modeling of static GMF in premises of houses with reinforced concrete structures was performed. The numerical results were experimentally confirmed. The recommendations for normalizing of GMF for creating safe and comfortable living conditions are given. These recommendations should be taken into account in designing modern premises of houses.

Стилі APA, Harvard, Vancouver, ISO та ін.

3

Грецьких, Світлана Володимирівна. "Ослаблення статичного геомагнітного поля феромагнітними елементами будинків". Thesis, НТУ "ХПІ", 2016. http://repository.kpi.kharkov.ua/handle/KhPI-Press/21433.

Повний текст джерела

Анотація:

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.09.05 – теоретична електротехніка. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2016. Дисертація присвячена математичному моделюванню явища ослаблення статичного геомагнітного поля (ГМП) в приміщеннях житлових будинків та розробці рекомендацій з методів його нормалізації до безпечного рівня. На прикладі циліндричної феромагнітної колони проведено моделювання ослаблення ГМП за допомогою методу еквівалентних (фіктивних) магнітних зарядів та розв’язано задачу розрахунку індукції ГМП, ослабленого протяжними феромагнітними елементами. Визначенні фізичні параметри феромагнітної колони, що впливають на інтенсивність ослаблення ГМП поблизу її поверхні, та умови зменшення до безпечного рівня інтенсивності ослаблення ГМП за рахунок зміни геометрії колони та зменшення початкової магнітної проникності її матеріалу. Здійснено розвиток методу ефективної магнітної проникності Аркадьєва для моделювання магнітного поля залізобетонних колон та міжповерхових перекриттів, армованих сталевим металопрокатом, та виконане чисельне моделювання інтенсивності ослаблення статичного ГМП в приміщеннях житлових будинків з несучими залізобетонними конструкціями і його верифікацію на основі результатів експерименту. Розроблені рекомендації з методів нормалізації ГМП при проектуванні сучасних житлових будинків для створення безпечних та комфортних умов проживання населення за статичним ГМП.
Thesis for scientific degree of candidate of technical sciences, specialty 05.09.05 – theoretical electrical engineering. – National Technical University "Kharkiv Polytechnic Institute", Kharkiv, 2016. The thesis is devoted to mathematical modeling of the phenomenon of weakening of the static geomagnetic field (GMF) in residential homes and to the development of recommendations on how to normalize it to a safe level. The modeling of weakening of the GMF was performed with the help of the equivalent charges method. The cylindrical ferromagnetic column was taken as an example. In the framework of this technique the problem of calculation of the GMF’s induction weakened by extended ferromagnetic elements was solved. The physical parameters of the ferromagnetic column which effect the weakening of GMF are determined. The conditions under which GMF is reduced to the safety level are also determined. This is due to the changes of the GMF’s geometry and reducing of initial magnetic permeability of its material. The Arcadiev method of the effective magnetic permeability for modeling of magneticfield of reinforced concrete columns and intermediate floors was developed. The numerical modeling of static GMF in premises of houses with reinforced concrete structures was performed. The numerical results were experimentally confirmed. The recommendations for normalizing of GMF for creating safe and comfortable living conditions are given. These recommendations should be taken into account in designing modern premises of houses.

Стилі APA, Harvard, Vancouver, ISO та ін.

4

Oliveira, Yuri Álisson Rodrigues de. "Contribuição ao estudo dos níveis de energia em sistemas contendo íons Ln3+." Universidade Federal de Sergipe, 2016. https://ri.ufs.br/handle/riufs/5258.

Повний текст джерела

Анотація:

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
A new approach to describe the crystal field interaction in compounds that contains trivalent lanthanide ions is presented. It is considered the electrostatic balance of the optically active site, the effective charge of the central ion and the sign of crystal field parameters (CCP) as determinant factors in the crystal field interaction. The method of the first equivalent neighbours (MENN) was reformulated, and improvements in predicting the CCP and energy levels 7FJ of Eu3+ could be realized. Moreover, it was possible to predict the lanthanide-nearest neighbour interaction of load factors (Ln-NN), the maximum coverage of the wave functions of the interacting ions and energy levels levels structure of the 7FJ of Eu3+. The physically acceptable limits are designed to load factors and the maximum overlap of the wave functions of the interacting ions. The compounds studied have high symmetry and exhibit a first neighbourhood consisting of oxygen ions, fluorine or chlorine. The use of secular determinants solutions of the energy matrices served as an excellent theoretical framework for the development of the method, which is applied based on the simple overlap model (SOM). This allowed the description of the interaction of the crystalline field by a nonparametric method and simple application. In addition, it was predicted the wave functions overlap factor of the interacting ions, the total effective bonding charge of Eu3+, and the relationships and trends of the crystal field interaction with the chemical species of the NN and the type of Ln that makes up the main host matrix. Finally, it was possible to remodulate the MENN at a more theoretical method by using theoretical data. The results served to confirm the efficiency and accuracy of MENN in describing the interaction of the crystal field on systems containing trivalent lanthanide ions.
Uma nova abordagem na descrição da interação do campo cristalino em compostos contendo íons lantanídeos trivalentes é apresentada. São considerados o equilíbrio eletrostático do sítio opticamente ativo, a carga efetiva do íon central e o sinal dos parâmetros de campo cristalino (PCC) como fatores determinantes na descrição da interação de campo cristalino. O método dos primeiros vizinhos equivalentes (MENN) foi reformulado, e assim melhorias na previsão dos PCC e dos níveis de energia 7FJ do Eu3+ puderam ser realizadas. Além disso, foi possível prever fatores de carga de interação lantanídeo-primeiro vizinho (Ln-PV), o recobrimento máximo das funções de onda dos íons interagentes e estrutura dos níveis níveis de energia 7FJ do Eu3+. Foram estabelecidos limites fisicamente aceitáveis para os fatores de carga e para o recobrimento máximo das funções de onda dos íons interagentes. Os compostos estudados possuem alta simetria e apresentam uma primeira vizinhança composta por íons de oxigênio, flúor ou cloro. A utilização das soluções dos determinantes seculares das matrizes energéticas serviram como um excelente aporte teórico para o desenvolvimento do método, o qual é aplicado tendo por base o modelo de recobrimento simples (SOM). Isto permitiu a descrição da interação do campo cristalino por um método não paramétrico e de simples aplicação. Além disso, foi realizada a previsão do fator de recobrimento das funções de onda dos íons interagentes, carga efetiva total de ligação do Eu3+, e as relações e tendências da interação do campo cristalino com a espécie química dos PV, e o tipo de Ln que compõe a matriz hospedeira principal. Por fim, foi possível tornar o MENN um método mais teórico através da utilização de dados teóricos. Os resultados obtidos serviram para confirmar a eficiência e precisão do MENN na descrição da interação do campo cristalino em sistemas contendo íons lantanídeos trivalentes.

Стилі APA, Harvard, Vancouver, ISO та ін.

5

Castellani, Adriano. "Calcul du champ electrique par la methode des charges equivalentes pour la simulation d'une decharge bi-leader." Paris 11, 1995. http://www.theses.fr/1995PA112269.

Повний текст джерела

Анотація:

On presente ici les differentes etapes de la realisation d'un code de calcul permettant l'evaluation des distributions de potentiel et de champ electrique lors du developpement d'un claquage a partir d'un objet electriquement flottant. La premiere partie de l'etude consiste en l'analyse experimentale en laboratoire de ce type de decharge, mettant en evidence le developpement bidirectionnel de deux decharges de polarites opposees a partir d'un conducteur isole (systeme de bi-leader). Le calcul de champ, derive de la methode des charges equivalentes, a ete concu pour prendre en compte les contributions des differents elements de ce bi-leader, canaux de leader et regions corona, puis integre dans un modele physique de simulation de la formation et de la propagation de la decharge. Dans cette perspective, des techniques de calcul specifiques ont ete mises en uvre de facon a permettre la representation de systemes variables au cours du temps, les distributions de champ et de potentiel pouvant ainsi etre recalculees a chaque pas de progression de la decharge. Les procedures de calcul de champ ont ete validees dans le cas de la decharge de laboratoire, puis transposees au cas de l'eclair declenche en altitude: dans les deux cas, la simulation numerique est en excellent accord avec les donnees experimentales. Enfin, cette methode de calcul de champ a ete extrapolee a l'etude de systeme tridimensionnels sans symetrie de rotation, en vue d'application futures a l'etude du foudroiement des aeronefs ou de structures au sol

Стилі APA, Harvard, Vancouver, ISO та ін.

6

Ekman, Jonas. "Electromagnetic modeling using the partial element equivalent circuit method." Doctoral thesis, Luleå, 2003. http://epubl.luth.se/1402-1544/2003/27.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

7

Munk, Jens. "An equivalent source inversion method for imaging complex structures /." The Ohio State University, 1999. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488191667184336.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

8

Becker, Ralf. "Consumption equivalent public capital method and a three generations model /." Marburg : Metropolis-Verl, 2002. http://www.gbv.de/dms/zbw/35493113X.pdf.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

9

Bécot, François-Xavier. "Tyre noise over impedance surfaces : efficient application of the equivalent sources method." Lyon, INSA, 2003. http://theses.insa-lyon.fr/publication/2003ISAL0036/these.pdf.

Повний текст джерела

Анотація:

Le but de ce travail est de comprendre et de contrôler les mécanismes de rayonnement du pneumatique, ceci en concevant des outils de prédiction efficients pour la propagation du bruit pneumatique / chaussée au dessus de surfaces d'impédances arbitraires. Le rayonnement du pneumatique est modélisé à l'aide de la méthode des Sources Equivalentes. Un modèle d'effets de sol dus à un plan d'impédance donnée est développé pour des sources de directivités arbitraire. Par ailleurs, la solution exacte du problème bi-dimensionel est présentée. Basé sur les deux outils de prédiction précédents, un modèle itératif est développé pour le rayonnement d'un pneumatique au-dessus de surfaces d'impédance arbitraire. A l'aide de ce nouvel outil, un étude paramétrique examine les tendances du rayonnement du pneumatique au-dessus de chaussées absorbantes. Le présent travail contribue à l'étude des possibilités de réduction du bruit du trafic, notamment en utilisant des chaussées dites silencieuses
The aim of the present work is to understand and to control the mechanisms of the tyre radiation, by designing efficient prediction tools for the propagation of the tyre / road noise over arbitrary impedance surfaces. Tyre radiation is modelled using the Equivalent Sources method. A model for the ground effects induced from a given impedance plane is developed for sources having arbitrary directivity. Moreover, the exact solution to the two-dimensional problem is derived. Based on the two previous prediction tools, an iterative model is developed for the tyre radiation over an arbitrary impedance surface. Using this model, a parametrical study examines the tendencies of tyre radiation over absorbing surfaces. The present work allows to study the possibilities of traffic noise reduction, particularly by the use of so-called silent road surfaces

Стилі APA, Harvard, Vancouver, ISO та ін.

10

Min, Ki-Bok. "Determination of equivalent hydraulic and mechanical properties of fractured rock masses using the distinct element method." Licentiate thesis, KTH, Land and Water Resources Engineering, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1550.

Повний текст джерела

Анотація:

The equivalent continuum approach uses equivalent propertiesof rock mass as the input data for a continuum analysis. Thisis a common modeling method used in the field of rock mechanicsand hydrogeology. However, there are still unresolvedquestions; how can the equivalent properties be determined andis the equivalent continuum approach suitable for modeling thediscontinuous fractured rock mass.

The purpose of this paper is to establish a methodology todetermine the equivalent hydraulic and mechanical properties offractured rock masses by explicit representations of stochasticfracture systems, to investigate the scale-dependency of theproperties, and to investigate the conditions for theapplication of the equivalent continuum approach for thefractured rock masses. Geological data used for this study arefrom the site characterization of Sellafield, Cumbria, UK. Aprogram for the generation of stochastic Discrete FractureNetwork (DFN) is developed for the realization of fractureinformation and ten parent DFN models are constructed based onthe location, trace length, orientation and density offractures. Square models with the sizes varying from 0.25 m× 0.25 m to 10 m × 10 m are cut from the center ofthe each parent network to be used for the scale dependencyinvestigation. A series of the models in a parent network arerotated in 30 degrees interval to be used for investigation oftensor characteristic. The twodimensional distinct elementprogram, UDEC, was used to calculate the equivalentpermeability and compliance tensors based on generalizedDarcys law and general theory of anisotropic elasticity.Two criteria for the applicability of equivalent continuumapproach were established from the investigation: i) theexistence of properly defined REV (Representative ElementaryVolume) and ii) existence of the tensor in describing theconstitutive equation of fractured rock The equivalentcontinuum assumption cannot be accepted if any one of the abovetwo criteria is not met. Coefficient of variation and meanprediction error is suggested for the measures toquantitatively evaluate the errors involved in scale dependencyand tensor characteristic evaluation.

Equivalent permeability and mechanical properties (includingelastic modulus and Poissons ratios) determined onrealistic fracture network show that the presence of fracturehas a significant effect on the equivalent properties. Theresults of permeability, elastic moduli and Poisson's ratioshow that they narrow down with the increase of scale andmaintain constant range after a certain scales with someacceptable variation. Furthermore, Investigations of thepermeability tensor and compliance tensor in the rotated modelshow that their tensor characteristics are satisfied at acertain scale; this would indicate that the uses of theequivalent continuum approach is justified for the siteconsidered in this study.

The unique feature of the thesis is that it gives asystematic treatment of the homogenization and upscaling issuesfor the hydraulic and mechanical properties of fractured rockswith a unified approach. These developments established a firmfoundation for future application to large-scale performanceassessment of underground nuclear waste repository byequivalent continuum analysis.

Keywords :Equivalent continuum approach, Equivalentproperty, Representative Elementary Volume (REV), DistinctElement Method, Discrete Fracture Network (DFN)

Стилі APA, Harvard, Vancouver, ISO та ін.

11

Min, Ki-Bok. "Fractured Rock Masses as Equivalent Continua - A Numerical Study." Doctoral thesis, KTH, Land and Water Resources Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3742.

Повний текст джерела

Анотація:

In this thesis, fractured rock masses are treated asequivalent continua for large-scale analyses of rockengineering projects. Systematic developments are made for thedetermination of equivalent mechanical and hydraulic propertiesof fractured rock masses using a hybrid discrete fracturenetwork - distinct element method (DFN-DEM) approach. Thedetermined equivalent properties are then used for a far-fieldfinite element analysis of the thermo-mechanical impacts on thestress, deformation and permeability of fractured rockssurrounding a hypothetical geological repository of nuclearwaste. The geological data were extracted from the results ofan extensive site investigation programme at Sellafield, UK,conducted by Nirex UK Ltd.

The scale dependencies of the hydraulic and mechanicalproperties were investigated by using multiple realizations ofthe fracture system geometry with increasing model sizes untilproperly defined hydraulic and mechanical representativeelementary volumes (REVs) were reached. The validity of thesecond order permeability tensor and the fourth-ordermechanical compliance tensor were tested for continuum analysesat larger scales. The REV was determined to be around 5 m formechanical and hydraulic data in this study.

Analysis of the stress-dependent mechanical and hydraulicproperties shows that the effect of rock stresses is crucial.The elastic moduli increase significantly with the increase ofstress and an empirical equation of stress-dependent elasticmodulus is suggested based on results of numerical experiments.Calculations of the Poisson's ratios suggest greater valuesthan are normally assumed in practice. Depending on the stateof stress, permeability decreases or increases with increasingcompressive stress. Stress-induced flow channeling effect iscaptured by numerical modeling for the first time and detailedmechanisms of shear dilation of fractures are provided. Basedon the numerical experiments, a set of empirical equations wassuggested for the stress-dependent permeability, consideringboth normal deformation and shear dilation of fractures.

Thermo-mechanical impact on the performance of ahypothetical repository at a far-field scale (5 km by 1 km) wasinvestigated with the stress-dependent equivalent propertiesdetermined at the REV scale. This analysis shows thatmechanical responses vary significantly depending on how themechanical properties were determined. The change ofpermeability due to the thermal loading is, however, notsignificant in this particular case.

The thesis provides a framework for systematic analysis oflarge-scale engineering applications in fractured rock masses,such as geological repositories of nuclear wastes.

Keyword:Fractured rock masses, Equivalent Continuum,Discrete Fracture Network (DFN), Distinct Element Method (DEM),Finite Element Method (FEM), Nuclear Waste Disposal, CoupledThermo-Hydro-Mechanical Processes

Стилі APA, Harvard, Vancouver, ISO та ін.

12

Vorfolomeyeva, Yuliya. "Nonlinear static analysis of rubble-stone masonry buildings performed with equivalent frame method." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.

Знайти повний текст джерела

Анотація:

Nonlinear static analysis is an efficient tool for performance assessment of masonry structures. In particular, it facilitates the accurate prediction of seismic response of a structure to earthquakes. Numerical models based on Equivalent Frame Method allow to predict realistic failure modes observed after preceding seismic events with reasonable computational effort, a characteristic which is suitable for engineering practice. This thesis deals with nonlinear incremental static (pushover) analysis of masonry buildings and the subsequent discussion of the obtained results. TreMuri software is used for developing the numerical models, which are then analysed on the basis of elastic acceleration response spectra obtained according to the Nepal National Building Code. Different structural improvement techniques are implemented in the models and compared in order to determine their impact on seismic performance. Elastic stiffness obtained with the nonlinear analysis is examined in contrast to analytical estimation of the same, made with various mathematical models.

Стилі APA, Harvard, Vancouver, ISO та ін.

13

Pitilakis, Dimitris. "Soil-structure interaction modeling using equivalent linear soil behavior in the substructure method." Châtenay-Malabry, Ecole centrale de Paris, 2006. http://www.theses.fr/2006ECAP1067.

Повний текст джерела

Анотація:

Une procédure numérique, ainsi qu’un code numérique (MISS3D-EqL), est développés pour prendre en compte le comportement nonlinéaire du sol dans l'interaction sol-structure. Le comportement linéaire équivalent est supposé pour le sol, alors que la réponse de la structure et ses effets sur le sol sont correctement pris en considération avec la méthode de sous-structuration dynamique. La procédure proposée est validée par d'autres logiciels numériques et moyens expérimentaux, comme des essais de tables vibrante et centrifugeuse. Les effets du comportement linéaire équivalent du sol sur la réponse du système sol-structure sont clairement démontrés par des analyses de cas représentatives. Une analyse des systèmes typiques de sol-structure est exécutée pour indiquer le ramollissement supplémentaire du système et l’augmentation de la dissipation d'énergie, comparé au cas linéaire. Considération particulière est donnée à l'évaluation des fonctions dynamiques d'impédance de la fondation. Les coefficients dynamiques de la rigidité et de l'amortissement radiatif sont estimés pour des fondations typiques posées sur des profils typiques de sol avec un comportement linéaire équivalent. Les effets du comportement nonlinéaire du sol sont montrés comparés au cas linéaire élastique. Le coefficient dynamique de rigidité se diminue avec l'augmentation de l'amplitude de l'accélération, avec la vitesse décroissante de cisaillement du sol et avec le module décroissant de cisaillement du sol, alors qu'il dépend de la contenue fréquentiel du séisme. Le coefficient de d'amortissement radiatif n’est pas affecté par le comportement nonlinéaire du sol, pour la plupart des applications pratiques
A numerical procedure, coded into a numerical code (MISS3D-EqL), is developed to accommodate for the effects of the nonlinear soil behavior on the soil-structure interaction (SSI) using an equivalent linear approach. Equivalent linear behavior is assumed for the soil, while the response of the structure to the ground shaking and its effects on the soil are properly taken into account using the substructure method. The proposed procedure is validated against other numerical software and experimental means, such as shaking table and centrifuge tests. The effects of the equivalent linear soil behavior on the soil-structure system response are clearly demonstrated by analyses of representative case studies. A recursive analysis of typical soil profiles and infrastructures is performed to reveal the further softening of the system and the increased energy dissipation, compared to the linear case, due to the equivalent linear soil behavior. Special emphasis is given to the estimation of the foundation dynamic impedance functions. Dynamic stiffness and radiation dashpot coefficients are estimated for typical footings resting on typical soil profiles with equivalent linear behavior. The effects of the nonlinear soil behavior on the dynamic coefficient are shown compared to the linear elastic case. The dynamic stiffness coefficient decreases with increasing input acceleration amplitude, with decreasing soil shear wave velocity and with decreasing soil shear modulus, while it depends on the frequency content of the earthquake. The radiation dashpot coefficient is unaffected by the nonlinear soil behavior for most practical applications

Стилі APA, Harvard, Vancouver, ISO та ін.

14

Ekman, Jonas. "The partial element equivalent circuit method : modeling and experimental verification of PCB structures." Licentiate thesis, Luleå tekniska universitet, EISLAB, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18244.

Повний текст джерела

Анотація:

To help products comply with international Electromagnetic Compatibility (EMC)regulations or as a help in a design process numerical simulation of electromagnetic (EM) characteristics are a valuable tool. With the development of high-speed computers the complexity of EM simulation programs and the systems they can simulate has increased considerable. But still, problems must be partitioned due to computer resource and/or EM simulation technique limitations. In this thesis, four different EM simulation techniques are described and the nature of these are discussed. The focus is on the partial element equivalent circuit (PEEC) method for which the following improvements and investigations have been proposed in the enclosed papers. First, a recent proposed formulation for the direct simulation of the radiated electric field from a device is compared against traditional post-processing equations and measurements. The results show that the proposed direct method, the electric field sensor, is unreliable for arbitrarily implementations since the length of the sensor strongly affects the results. Second, a technique to obtain simplified PEEC models are presented. The first step is to use a discretisation procedure where partial elements with small effect on the complete PEEC model are excluded. Then, instead of using numerical integration, closed-form equations are used to calculate the partial elements. The obtained simplified PEEC models are shown to comply well against measurements. Third, an introductory paper to the PEEC method is presented. The international interest for the method has been gaining rapidly for the past years resulting in considerable progress for the technique. But, in the Nordic countries the research effort has been low. The paper presents the technique using simple antenna examples, both printed and free space, and illustrations. For verification, simulations have been compared against analytical solutions and measurements.
Godkänd; 2001; 20070314 (ysko)

Стилі APA, Harvard, Vancouver, ISO та ін.

15

Lau, Mark C. "Small Signal Equivalent Circuit Extraction From A Gallium Arsenide MESFET Device." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36952.

Повний текст джерела

Анотація:

The development of microwave Gallium Arsenide Metal Semiconductor Field Effect Transistor (MESFET) devices has enabled the miniaturization of pagers, cellular phones, and other electronic devices. With these MESFET devices comes the need to model them. This thesis extracts a small signal equivalent circuit model from a Gallium Arsenide MESFET device. The approach taken in this thesis is to use measured S- parameters to extract a small signal equivalent circuit model by optimization. Small signal models and S-parameters are explained. The Simplex Method is used to optimize the small signal equivalent circuit model. A thorough analysis of the strengths and weaknesses of the Simplex method is performed.
Master of Science

Стилі APA, Harvard, Vancouver, ISO та ін.

16

Poumarat, Georges. "L'entraînement à l'aide de charges additionnelles." Clermont-Ferrand 2, 1986. http://www.theses.fr/1986CLF21500.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

17

DiRienzo, Adriano Carleton University Dissertation Engineering Civil and Environmental. "A study of the equivalent frame method of analysis for flat plate building systems." Ottawa, 1995.

Знайти повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

18

SANTOS, RODRIGO BIANCHI. "PARAMETRIC OPTIMIZATION OF TRUSS STRUCTURES UNDER DYNAMIC LOADING USING THE EQUIVALENT STATIC LOAD METHOD." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2018. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=35802@1.

Повний текст джерела

Анотація:

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
Otimização estrutural sujeita a carregamentos dinâmicos é um problema desafiador em vários aspectos, a começar pelo grande número de restrições que devem ser atendidas em todos os instantes de tempo. Além disso, o custo computacional para avaliar os gradientes destas restrições é bastante elevado e requer um grande espaço de armazenamento. Na literatura, alguns métodos reduzem o número de restrições avaliando em instantes de tempo selecionados, como o pior caso por exemplo, ou ainda constroem um funcional equivalente, integrando as restrições violadas ao longo do tempo, assim eliminando essa dependência. Nesta dissertação, o método do Carregamento Estático Equivalente (ESL) é utilizado, no qual o problema dinâmico original é transformado em uma sequência de subproblemas de otimização linear estática com múltiplos casos de carga. Um atrativo deste método é a possibilidade da solução de problemas não lineares, evitando o alto custo devido às repetidas análises estruturais e cálculos das restrições. Problemas clássicos de treliças planas submetidas a carregamentos dinâmicos são resolvidos utilizando o método ESL. A função a ser minimizada é a massa da treliça, que está sob restrições de tensão e deslocamento, onde as variáveis de projeto são as áreas da seção transversal dos membros. Além disso, uma interface utilizando ANSYS e MATLAB é desenvolvida para uma abordagem modular, na qual a análise via elementos finitos e a otimização possam ser realizadas separadamente. Este processo viabiliza a otimização de estruturas que apresentam comportamentos não lineares a partir da utilização de diversos softwares comerciais disponíveis no mercado.
Structural optimization subject to dynamic loading is a challenging problem in many aspects, starting with the large number of constraints that must be respected at all instants of time. Furthermore, the computational cost to evaluate the gradients of these constraints is significantly high and requires a large storage space. In the literature, some methods reduce the number of constraints evaluating at selected instants of time, such as the worst case. Alternatively, a single equivalent functional is constructed to eliminate the time dependence by integrating the violated constraints over time. In this work, the Equivalent Static Load (ESL) method is used, in which the original dynamic problem is reduced into a number of static linear optimization problems with multiple load cases. An attractive feature of this method is the possibility of solving non-linear problems, avoiding the high cost due to repeated structural analyzes and constraint calculations. Classical problems of plane trusses subjected to dynamic loads are solved using the ESL method. The function to be minimized is the truss mass, which is subjected to stress and displacement constraints, where the design variables are the cross-sectional areas of the members. In addition, an interface using ANSYS and MATLAB was developed for a modular approach, in which finite element analysis and optimization can be performed separately. This process makes possible the optimization of structures that present non-linear behavior from the use of most structural analysis software packages available on the market.

Стилі APA, Harvard, Vancouver, ISO та ін.

19

Prinsloo, Etienne Pieter Willem. "Fatigue equivalent static load: Methodology for the design of vehicle structures." Diss., University of Pretoria, 2003. http://hdl.handle.net/2263/25966.

Повний текст джерела

Анотація:

This study is concerned with the design of vehicle structures through the use of Fatigue Equivalent Static Loads (FESL). A large percentage of failures of mechanical structures can be attributed to fatigue. Furthermore, it is also generally accepted that defective structural design is mostly caused by insufficient knowledge of the input loading. The fatigue loads experienced by vehicle structures are especially difficult to quantify. In the current competitive markets, it is essential to use a pro-active, timely and cost effective process to solve fatigue related problems. The heart of the FESL methodology is the ability to condense a large amount of input load data into a single fatigue load. This is achieved by calculating the damage of the measurements and converting it to an equivalent stress, through the use of a calibration matrix obtained from a unit-load finite element analysis. A Fatigue Equivalent Static Load can now be determined, and the vehicle structure can be evaluated for durability.
Dissertation (M Eng (Mechanical Engineering))--University of Pretoria, 2003.
Mechanical and Aeronautical Engineering
unrestricted

Стилі APA, Harvard, Vancouver, ISO та ін.

20

Nielsen, Adam Derek. "Monte Carlo calculation of fluence-to-ambient dose equivalent conversion coefficients for high-energy neutrons." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/16424.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

21

Edwards, Micael Cuin. "A Method for Determining Weight Reduction through Material Substitution in Automotive Structures of Equivalent Stiffness." MSSTATE, 2002. http://sun.library.msstate.edu/ETD-db/theses/available/etd-11302001-165029/.

Повний текст джерела

Анотація:

The benefits of lighter auto bodies are discussed, and aluminum is compared to steel as an alternative material for auto body construction. The concept of a structural index, lambda, is developed using the simple example of a hollow beam of wall thickness, t, with a cantilever load case. It is shown that the bending stiffness, K, of the beam can be defined as a function of t^lambda, that 1 < lambda < 3, and that lambda can be used to predict the weight savings from material substitution where stiffness is held constant. It is then demonstrated that lambda can be used to predict the weight savings from material substitution in the more complex cases of the joints of a light truck cab.

Стилі APA, Harvard, Vancouver, ISO та ін.

22

Tchorowski, Leo A. "Sparse-Constrained Equivalent Element Distribution Method to Represent Measured Antenna Data in Numerical Electromagnetics Codes." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1582877220383629.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

23

Leinonen, M. (Mikko). "Finite element method and equivalent circuit based design of piezoelectric actuators and energy harvester dynamics." Doctoral thesis, Oulun yliopisto, 2015. http://urn.fi/urn:isbn:9789526208374.

Повний текст джерела

Анотація:

Abstract The main objective of this thesis was to use and combine Finite Element Method (FEM) and small signal equivalent circuit models in actuator and energy harvesting design and to study the dynamics of the said designs. The work is divided into four different sections. In the first section, the small signal parameters are derived for a pre-stressed piezoelectric actuator using a series of measurements. In addition, the tunability of the resonance frequency using mass and series capacitors is investigated. In the second section, a piezoelectric Fabry Perot Interferometer actuator is simulated using FEM and the small signal parameters are derived using FEM simulations. The modelled results are compared with the actual measurements and the resonance frequency is found to differ by only 0.8 percent from the measured values when the mirror is attached to the actuator. In the third section a piezoelectric wide band energy harvester is developed with multiple beam topology. Two different designs are compared, one produced using the conventional PZT-steel structure and one with a PZT-LTCC structure. The final section presents an FEM model for a shoe mounted energy harvester and concentrates on the modelling of walking dynamics in FEM. The simulation results are compared to actual measurements and the simulated power values are found to differ by only 7% when the cymbal stroke is below 1.3 mm. The generated model is also expandable to other types of energy harvesters and the methods developed can be used in a variety of different energy harvesting simulations and harvester development. The results show that the equivalent circuit approach together with FEM modelling is a powerful tool in the dynamics design of piezoelectric actuators and energy harvesters
Tiivistelmä Väitöstyön päätavoitteena oli yhdistää elementtimenetelmät (FEM) ja piensignaalimallit aktuaattorien ja energiankorjuukomponenttien suunnittelussa ja tutkia niiden dynamiikkaa. Työ on jaettu neljään eri osaan. Ensimmäisessä osassa piensignaalimallit johdettiin pietsosähköisestä aktuaattorista mittausten avulla. Lisäksi resonanssitaajuuden muuttamista tutkitaan massan ja sarjaan kytketyn kapasitanssin avulla. Toisessa osassa simuloidaan pietsosähköistä Fabry Perot interferometria käyttäen elementtimenetelmää. Lisäksi komponentin piensignaalimalli luodaan käyttäen simulointimallia. Lopuksi piensignaalimallin ja prototyypin mittaustuloksia verrataan. Mallin resonanssitaajuus poikkeaa mitatusta vain 0.8 %, kun aktuaattoriin on kiinnitetty peili. Kolmannessa osassa kehitetään ja verrataan toisiinsa kahta erilaista laajakaistaista monipalkkista pietsosähköistä energian korjuukomponenttia. Toinen komponenteista on toteutettu perinteisellä PZT-teräs rakenteella ja toinen yhteissintratulla PZT-LTCC rakenteella. Viimeisessä osassa luodaan simulaatio malli kenkään asennetulle cymbal tyyppiselle pietsosähköiselle energian korjuukomponentille ja kävelyn dynamiikkaa tutkitaan. Luotua mallia verrataan prototyypin mittaustuloksiin ja simuloitu energian tuotto poikkeaa vain 7 % alle 1.3 mm puristusliikkeellä. Tulokset osoittivat, että piensignaalimallin ja elementtimenetelmän yhdistäminen on tehokas apu pietsosähköisten aktuaattorien ja energiankorjuukomponenttien dynamiikan suunnittelussa

Стилі APA, Harvard, Vancouver, ISO та ін.

24

Ismatullah. "Analysis of space-borne antennas by higher-order method of moments and inverse equivalent current methods." kostenfrei, 2010. https://mediatum2.ub.tum.de/node?id=977261.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

25

Fabbiani-Leon, Angelique Marie. "Comparison method between gridded and simulated snow water equivalent estimates to in-situ snow sensor readings." Thesis, University of California, Davis, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1604056.

Повний текст джерела

Анотація:

California Department of Water Resources (DWR) Snow Surveys Section has recently explored the potential use of recently developed hydrologic models to estimate snow water equivalent (SWE) for the Sierra Nevada mountain range. DWR Snow Surveys Section’s initial step is to determine how well these hydrologic models compare to the trusted regression equations, currently used by DWR Snow Surveys Section. A comparison scheme was ultimately developed between estimation measures for SWE by interpreting model results for the Feather River Basin from: a) National Aeronautics and Space Administration (NASA) Jet Propulsion Laboratory (JPL) gridded SWE reconstruction product, b) United States Geological Survey (USGS) Precipitation-Runoff Modeling System (PRMS), and c) DWR Snow Surveys Section regression equations. Daily SWE estimates were extracted from gridded results by computing an average SWE based on 1,000 ft elevation band increments from 3,000 to 10,000 ft (i.e. an elevation band would be from 3,000 to 4,000 ft). The dates used for processing average SWE estimates were cloud-free satellite image dates during snow ablation months, March to August, for years 2000–2012. The average SWE for each elevation band was linearly interpolated for each snow sensor elevation. The model SWE estimates were then compared to the snow sensor readings used to produce the snow index in DWR’s regression equations. In addition to comparing JPL’s SWE estimate to snow sensor readings, PRMS SWE variable for select hydrologic response units (HRU) were also compared to snow sensor readings. Research concluded with the application of statistical methods to determine the reliability in the JPL products and PRMS simulated SWE variable, with results varying depending on time duration being analyzed and elevation range.

Стилі APA, Harvard, Vancouver, ISO та ін.

26

Carwile, Zachary Thomas. "Validation of a 3-D Virtual Acoustic Prototyping Method For Use In Structural Design." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/30988.

Повний текст джерела

Анотація:

Virtual acoustic prototyping (auralization) is the rendering of a virtual sound field that is created from the calculated acoustic response of a modeled structure. Auralization is useful in the design and subjective evaluation of buildings, automobiles, and aircraft. The virtual acoustic prototyping method in this thesis uses finite element modeling (FEM), the equivalent source method (ESM), and head-related transfer functions (HRTFs). A tradeoff exists between the accuracy of the auralization process and the number of equivalent sources (and thus computational power) that are required. The goal of this research is to validate (numerically and subjectively) a virtual acoustic prototyping method for use in structural design; this thesis illustrates the first attempt to apply the aforementioned methods to a structure that represents a typical building or automobile. The structureâ s acoustics were modeled using FEM, ESM, and HRTFs. A prototype of the modeled structure was built. A 36% correlation was achieved between the model and prototype. Slight variations in boundary conditions caused significant FEM error, but the data represented a typical structure. Psychoacoustic comparison testing was performed to determine the number of equivalent sources that must be used in an auralization to accurately recreate the sound field. The number was found to be dependent on the type of noise that is played to the test subject. A clear relationship between the numerical correlation of two sounds and the percentage of subjects who could hear a difference between those two sounds was established for impulsive, broadband, and engine noises.
Master of Science

Стилі APA, Harvard, Vancouver, ISO та ін.

27

Balling, Lukas. "A Comparison of Optimized Nonlinear Time History Analysis and the Equivalent Lateral Forces Method for Brace Design." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd2086.pdf.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

28

Wernet, Jack R. "Comparison of the Statically Equivalent Serial Chain Center of Mass Estimation Method to OpenSim's Residual Reduction Algorithm." University of Dayton / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1628009554478147.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

29

Sugden, Frank Daniel. "A NOVEL DUAL MODELING METHOD FOR CHARACTERIZING HUMAN NERVE FIBER ACTIVATION." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1318.

Повний текст джерела

Анотація:

Presented in this work is the investigation and successful illustration of a coupled model of the human nerve fiber. SPICE netlist code was utilized to describe the electrical properties of the human nervous membrane in tandem with COMSOL Multiphysics, a finite element analysis software tool. The initial research concentrated on the utilization of the Hodgkin-Huxley electrical circuit representation of the nerve fiber membrane. Further development of the project identified the need for a linear circuit model that more closely resembled the McNeal linearization model augmented by the work of Szlavik which better facilitated the coupling of both SPICE and COMSOL programs. Related literature was investigated and applied to validate the model. This combination of analysis tools allowed for the presentation of a consistent model and revealed that a coupled model produced not only a qualitatively comparable, but also a quantitatively comparable result to studies presented in the literature. All potential profiles produced during the simulation were compared against the literature in order to meet the purpose of presenting an advanced computational model of human neural recruitment and excitation. It was demonstrated through this process that the correct usage of neuron models within a two dimensional conductive space did allow for the approximate modeling of human neural electrical characteristics.

Стилі APA, Harvard, Vancouver, ISO та ін.

30

Shrestha, Santosh. "A COMPARATIVE STUDY OF EQUIVALENT LATERAL FORCE METHOD AND RESPONSE SPECTRUM ANALYSIS IN SEISMIC DESIGN OF STRUCTURAL FRAMES." OpenSIUC, 2019. https://opensiuc.lib.siu.edu/theses/2561.

Повний текст джерела

Анотація:

Equivalent Lateral Force Method (ELF) and Response Spectrum Analysis (RSA) are the two most popular methods of seismic design of structures. This study aims to present a comparative study of the two methods using hand-calculated approach as well as computer analysis according to ASCE 7-10 Standards. The two methods have been compared in terms of base shear and story forces by analyzing various models for different number of stories and different support conditions. It was found that ELF gives conservative results in comparison to RSA. This result was more obvious in case of four-story frames. Hence, for structures of increased elevation, the analysis from ELF may not be sufficient.

Стилі APA, Harvard, Vancouver, ISO та ін.

31

Lázaro, Navarro Mario. "The Eigenvalue Problem in Linear Viscoelastic Structures: New Numerical Approaches and the Equivalent Viscous Model." Doctoral thesis, Universitat Politècnica de València, 2013. http://hdl.handle.net/10251/30062.

Повний текст джерела

Анотація:

El análisis y el control de las vibraciones cobra especial importancia en muchas ramas de la ingeniería, en especial la ingeniería mecánica, civil, aeronáutica y automovilística. Tal es así que prácticamente se identi¿ca como un área independiente dentro del análisis dinámico de estructuras. Desde los comienzos de esta teoría, las fuerzas disipativas o de amortiguamiento han sido uno de los fenómenos más difíciles de modelizar. El modelo viscoso, por su sencillez y versatilidad ha sido y sigue siendo el gran paradigma de los modelos de amortiguamiento. Sin embargo, como consecuencia de la aparición de materiales con memoria se introdujo el fenómeno de la viscoelasticidad; Esta, si bien está también 'íntimamente ligada ' a la velocidad de la respuesta, necesito de la introducción de las denominadas funciones hereditarias, que permiten poner a las fuerzas disipativas como función no solo de la velocidad instantánea sino de la historia de velocidades desde el comienzo del movimiento, de ahí el termino memoria. De forma natural, el avance teórico introducido en el modelo supone también una complicación computacional, pues donde antes teníamos un sistema lineal de ecuaciones diferenciales ahora tenemos un sistema de ecuaciones integro-diferenciales. El análisis de las vibraciones libres de los sistemas con amortiguamiento viscoelástico conduce a un problema nolineal de autovalores donde la característica principal es una matriz de amortiguamiento que depende de la frecuencia de excitación. El estudio de la solución de autovalores y autovectores de este problema es importante si se desean conocer los modos de vibración de la estructura o si se pretende obtener la respuesta en el dominio de la frecuencia del sistema. El objetivo fundamental de esta Tesis Doctoral es doble: Por un lado, profundizar en el conocimiento del problema de autovalores de sistemas viscoelásticos proponiendo para ello nuevos métodos numéricos de resolución. Por otro, desarrollar un nuevo modelo viscoso que, bajo ciertas condiciones, reproduzca la respuesta del modelo viscoelástico con su¿ciente aproximación. La Tesis se divide en ocho capítulos, de ellos el cuerpo principal se encuentra en los seis centrales (Capítulos 2 a 7. Todos ellos son artículos de investigación que, o bien han sido publicados, o bien están en proceso de revisión en revistas contenidas en el Journal Citation Reports (JCR). Por esta razón, todos los capítulos conservan la estructura intrínseca de un artículo, incluidas una introducción y una bibliografía en cada uno. Los cuatro primeros capítulos (Capítulos 2 a 5) se centran en el estudio del problema no lineal de autovalores. Se proponen dos metodologías de resolución: la primera es un procedimiento iterativo basado en el esquema del punto-¿jo y desarrollado para sistemas proporcionales o ligeramente no-proporcionales (aquellos en los que los modos se presentan desacoplados o casi desacoplados). La segunda metodología (presentada en dos capítulos diferentes), denominada paramétrica, permite obtener soluciones casi-analíticas de los autovalores, tanto para sistemas de un grado de libertad como para sistemas de múltiples grados de libertad y dentro de 'estos, para sistemas proporcionales y no proporcionales. El estudio del problema de autovalores se completa con un capítulo dedicado a los autovalores reales, también denominados autovalores no viscosos. En 'él se demuestra una nueva caracterización maten ática que deben cumplir dichos autovalores y que permite proponer un nuevo concepto: el conjunto no-viscoso. Los dos 'últimos capítulos (Capítulos 6 y 7) analizan el Modelo Viscoso Equivalente como propuesta para la modelización de la respuesta de sistemas viscoelásticos. El análisis se realiza desde el dominio de la frecuencia estudiando la función de transferencia. En una primera etapa (pen último capítulo), de naturaleza más maten ática, se demuestra que la función de transferencia exacta de un modelo viscoelástico se puede expresar como suma de una función de transferencia propia de un modelo viscoso más un término denominado residual, directamente dependiente del nivel de amortiguamiento inducido y del acoplamiento modal (noproporcionalidad de la matriz de amortiguamiento). En una segunda etapa ('ultimo capítulo), se desarrolla una aplicación para estructuras reales formadas por entramados planos de elementos 1D amortiguados con capas de material visco elástico. Este tipo de estructuras ha permitido usar una variante mejorada del método paramétrico para la obtención de los autovalores, de forma que en este 'ultimo capítulo ha servido como nexo de unión de las metodologías más importantes desarrolladas en la Tesis.
Lázaro Navarro, M. (2013). The Eigenvalue Problem in Linear Viscoelastic Structures: New Numerical Approaches and the Equivalent Viscous Model [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/30062
TESIS

Стилі APA, Harvard, Vancouver, ISO та ін.

32

Kabiri, Far Bardia. "Application of the Equivalent Static Analysis method to the design of a steel frame structure with added viscous dampers." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/10647/.

Повний текст джерела

Анотація:

All the structures designed by engineers are vulnerable to natural disasters including floods and earthquakes. The energy released during strong ground motions should be dissipated by structural elements. Before 1990’s, this energy was expected to be dissipated through the beams and columns which at the same time were a part of gravity-load-resisting system. However, the main disadvantage of this idea was that gravity-resisting-frame was not repairable. Hence, during 1990’s, the idea of designing passive energy dissipation systems, including dampers, emerged. At the beginning, main problem was lack of guidelines for passive energy dissipation systems. Although till 2000 many guidelines and procedures where published, yet most of them were based on complicated analysis which was not so convenient for engineers and practitioners. In order to solve this problem recently some alternative design methods are proposed including 1. Lopez Garcia (2001) simple procedure for optimal damper configuration in MDOF structures 2. Christopoulos and Filiatrault (2006) trial and error procedure 3. Silvestri et al. (2010) Five-Step Method. 4. Palermo et al. (2015) Direct Five-Step Method. 5. Palermo et al. (2016) Simplified Equivalent Static Analysis (ESA). In this study, effectiveness and differences between last three alternative methods have been evaluated.

Стилі APA, Harvard, Vancouver, ISO та ін.

33

Karaagacli, Taylan. "Determination Of Dynamically Equivalent Fe Models Of Aircraft Structures By Using Modal Test Data." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612522/index.pdf.

Повний текст джерела

Анотація:

Reliable flutter analysis of aircraft structures is a major requirement to determine safe flight envelops. Dynamically equivalent finite element model of an aircraft structure correlating well with experimental modal is a major requirement for a reliable flutter analysis. Currently available model updating techniques require enormous time and engineering work to achieve appropriate finite element models of aircraft structures. The method developed within the scope of this thesis work aims to remove important disadvantages of common model updating procedures. In doing this, the method starts with a simple finite element mesh obtained by connecting measurement points, used in the Ground Vibration Test of an aircraft structure, with 3 D Euler-Bernoulli beam elements. Initial estimates of the geometric and material properties are determined by solving structural identification equations derived from the mass and stiffness orthogonality of experimental modes. By using those initial estimates, an initial finite element model is constructed. Starting from this initial finite element model, structural identification equations are updated and solved iteratively by using experimental natural frequencies and eigenvectors of the v updated finite element model representing the same mode shapes with measured normal modes. Iterations are continued until eigen solution of the updated finite element model closely correlates with experimental modal data. The applicability of the method is illustrated on a scaled aircraft model and a real aircraft structure. The results are quite satisfactory but the method requires further improvements to achieve a much better correlation level in case of real aircraft structures.

Стилі APA, Harvard, Vancouver, ISO та ін.

34

Vauchelet, Nicolas. "Modélisation mathématique du transport diffusif de charges partiellement quantiques." Phd thesis, Université Paul Sabatier - Toulouse III, 2006. http://tel.archives-ouvertes.fr/tel-00135114.

Повний текст джерела

Анотація:

Le travail de la thèse concerne la modélisation et l'analyse
mathématique du transport d'électrons confinés dans une nanostructure
dans le but d'implémenter des simulations numériques. Dans de tels
dispositifs nanométriques, les ordres de grandeurs ne jouent pas le
même rôle dans chaque direction. Les électrons peuvent être
extrêmement confinés dans une ou plusieurs directions. Un modèle
quantique est nécessaire pour décrire le confinement. Dans la
direction non confinée, le transport est supposé de nature classique.
Nous proposons alors un système couplé quantique/classique.
Les collisions intervenant lors du transport induisent un régime
diffusif des porteurs de charges. Le modèle diffusif est obtenu grâce
à une limite de diffusion d'un modèle cinétique. L'analyse
mathématique de cette limite de diffusion et du modèle diffusif couplé
sont présentées. Une simulation numérique du transport dans un
nanotransistor est obtenue avec ce modèle.

Стилі APA, Harvard, Vancouver, ISO та ін.

35

Carloni, Federico. "A 3D model based on the SAM Method for seismic studies of masonry buildings." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/17151/.

Повний текст джерела

Анотація:

L'elaborato propone un metodo per la modellazione tridimensionale di interi edifici in muratura, con lo scopo di valutare le performance sismiche, mediante il programma di calcolo SAP2000. La metodologia proposta consente la modellazione di pareti in muratura simulandone il comportamento non lineare sotto azioni agenti nel piano ed allo stesso tempo permette di considerare la ripartizione delle azioni verticali e soprattutto orizzontali che avviene tra le pareti, dovuta alle zone di connessione, ai solai ed alla loro rigidezza a taglio nel piano. Per lo sviluppo del metodo di modellazione è stato utilizzato un edificio molto semplice. Successivamente la metodologia è stata applicata ad un caso più realistico sul quale si sono fatte anche considerazioni riguardo i diversi comportamenti della struttura in funzione della rigidezza dei solai.

Стилі APA, Harvard, Vancouver, ISO та ін.

36

Genest, Laurent. "Optimisation de forme par gradient en dynamique rapide." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEC022/document.

Повний текст джерела

Анотація:

Afin de faire face aux nouveaux challenges de l’industrie automobile, les ingénieurs souhaitent appliquer des méthodes d’optimisation à chaque étape du processus de conception. En élargissant l’espace de conception aux paramètres de forme, en augmentant leur nombre et en étendant les plages de variation, de nouveaux verrous sont apparus. C’est le cas de la résistance aux chocs. Avec les temps de calcul long, la non-linéarité, l’instabilité et la dispersion numérique de ce problème de dynamique rapide, la méthode usuellement employée, l’optimisation par plan d’expériences et surfaces de réponse, devient trop coûteuse pour être utilisée industriellement. Se pose alors la problématique suivante : Comment faire de l’optimisation de forme en dynamique rapide avec un nombre élevé de paramètres ?. Pour y répondre, les méthodes d’optimisation par gradient s’avèrent être les plus judicieuses. Le nombre de paramètres a une influence réduite sur le coût de l’optimisation. Elles permettent donc l’optimisation de problèmes ayant de nombreux paramètres. Cependant, les méthodes classiques de calcul du gradient sont peu pertinentes en dynamique rapide : le coût en nombre de simulations et le bruit empêchent l’utilisation des différences finies et le calcul du gradient en dérivant les équations de dynamique rapide n’est pas encore disponible et serait très intrusif vis-à-vis des logiciels. Au lieu de déterminer le gradient, au sens classique du terme, des problèmes de crash, nous avons cherché à l’estimer. L’Equivalent Static Loads Method est une méthode permettant l’optimisation à moindre coût basée sur la construction d’un problème statique linéaire équivalent au problème de dynamique rapide. En utilisant la dérivée du problème équivalent comme estimation du gradient, il nous a été possible d’optimiser des problèmes de dynamique rapide ayant des épaisseurs comme variables d’optimisation. De plus, si l’on construit les équations du problème équivalent avec la matrice de rigidité sécante, l’approximation du gradient n’en est que meilleure. De cette manière, il est aussi possible d’estimer le gradient par rapport à la position des nœuds du modèle de calcul. Comme il est plus courant de travailler avec des paramètres CAO, il faut déterminer la dérivée de la position des nœuds par rapport à ces paramètres. Nous pouvons le faire de manière analytique si nous utilisons une surface paramétrique pour définir la forme et ses points de contrôle comme variables d’optimisation. Grâce à l’estimation du gradient et à ce lien entre nœuds et paramètres de forme, l’optimisation de forme avec un nombre important de paramètres est désormais possible à moindre coût. La méthode a été développée pour deux familles de critères issues du crash automobile. La première est liée au déplacement d’un nœud, objectif important lorsqu’il faut préserver l’intégrité de l’habitacle du véhicule. La seconde est liée à l’énergie de déformation. Elle permet d’assurer un bon comportement de la structure lors du choc
In order to face their new industrial challenges, automotive constructors wish to apply optimization methods in every step of the design process. By including shape parameters in the design space, increasing their number and their variation range, new problematics appeared. It is the case of crashworthiness. With the high computational time, the nonlinearity, the instability and the numerical dispersion of this rapid dynamics problem, metamodeling techniques become to heavy for the standardization of those optimization methods. We face this problematic: ”How can we carry out shape optimization in rapid dynamics with a high number of parameters ?”. Gradient methods are the most likely to solve this problematic. Because the number of parameters has a reduced effect on the optimization cost, they allow optimization with a high number of parameters. However, conventional methods used to calculate gradients are ineffective: the computation cost and the numerical noise prevent the use of finite differences and the calculation of a gradient by deriving the rapid dynamics equations is not currently available and would be really intrusive towards the software. Instead of determining the real gradient, we decided to estimate it. The Equivalent Static Loads Method is an optimization method based on the construction of a linear static problem equivalent to the rapid dynamic problem. By using the sensitivity of the equivalent problem as the estimated gradient, we have optimized rapid dynamic problems with thickness parameters. It is also possible to approximate the derivative with respect to the position of the nodes of the CAE model. But it is more common to use CAD parameters in shape optimization studies. So it is needed to have the sensitivity of the nodes position with these CAD parameters. It is possible to obtain it analytically by using parametric surface for the shape and its poles as parameters. With this link between nodes and CAD parameters, we can do shape optimization studies with a large number of parameters and this with a low optimization cost. The method has been developed for two kinds of crashworthiness objective functions. The first family of criterions is linked to a nodal displacement. This category contains objectives like the minimization of the intrusion inside the passenger compartment. The second one is linked to the absorbed energy. It is used to ensure a good behavior of the structure during the crash

Стилі APA, Harvard, Vancouver, ISO та ін.

37

DESCLOS, STEPHANE. "Etude et calcul des distributions de courant et de tension sur une croix doublement fendue chargee par des diodes a l'aide d'une methode t. E. M. Calcul de la s. E. R. Equivalente." Rennes 1, 1991. http://www.theses.fr/1991REN10144.

Повний текст джерела

Анотація:

Cette these est l'etude theorique par une methode d'approximation quasi t. E. M. De doublet filaire et d'antenne plaque en forme de croix doublement fendue chargee par des diodes, a la reception. L'approche numerique est basee principalement sur la modelisation du motif etudie par des lignes de transmission. Cette methode permet de determiner les distributions de tension et de courant sur le motif a partir des conditions aux limites. La connaissance des distributions de courant en module et en phase permet de determiner le champ rerayonne a grande distance et par consequent, les surfaces equivalentes radar (monostatique et bistatique) du modele. L'insertion d'une impedance de charge au centre du doublet ou dans les fentes du motif permet par ailleurs de modifier ces surfaces equivalentes radar

Стилі APA, Harvard, Vancouver, ISO та ін.

38

Steif, Bassam. "Formulation courants et charges pour la résolution par équations intégrales des équations de l'électromagnétisme." Thesis, Toulouse, INSA, 2012. http://www.theses.fr/2012ISAT0028/document.

Повний текст джерела

Анотація:

Cette thèse a consisté à élaborer une méthode qui permet de résoudre l’équation intégrale comportant comme inconnues les courants et les charges introduite récemment par Taskinen et Ylä-Oijala par une méthode d’éléments frontière sans aucune contrainte de continuité au niveau des interfaces des éléments aussi bien pour les courants que pour les charges. Nous avons d’abord montré comment on pouvait construire cette équation de façon simple et similaire à celle des formulations intégrales usuelles en imposant au problème intérieur relatif au système de Picard, qui est en fait une extension du système de Maxwell, des conditions aux limites adéquates. Pour des géométries régulières de l’objet diffractant, nous avons établi de façon théorique la stabilité et la convergence des schémas numériques ci-dessus en montrant que cette équation peut être décomposée sous la forme d’un système elliptique coercif et d’un opérateur compact dans le cadre des fonctions de carré intégrable.Toute cette étude a été confirmée par des tests numériques tridimensionnels. Comme pour les équations intégrales usuelles de seconde espèce, le cadre théorique valable pour des surfaces régulières ne l’est plus pour des surfaces avec des singularités. L’utilisation formelle de cette équation,pour des surfaces singulières, a donné des résultats entachés d’erreur. Nous avons mis en évidence l’origine des instabilités numériques à l’origine de ces erreurs lorsque les géométries sont singulières en développant une version bidimensionnelle de cette équation. Cette version nous a permis en particulier de montrer que les instabilités étaient dues à des oscillations parasites concentrées autour des singularités de la géométrie. Dans ce cadre nous avons pu mettre en oeuvre plus aisément des approches pour supprimer ou atténuer ces oscillations parasites ou leur effet sur les calculs en champ lointain. Nous avons montré qu’un procédé d’augmentation des degrés de liberté pour la charge par rapport au courant pouvait sensiblement réduire ces instabilités. A la suite de l’amélioration observée sur les résultats dans le cas 2D, nous avons transposé cette procédure au cas tridimensionnel. A travers divers tests, nous avons constaté l’amélioration de la qualité de l’approximation amenée par la procédure de stabilisation
The objective of this thesis was to develop a method that solves the integral equation whose unknowns are the currents and the charges, recently introduced by Taskinen and Ylä-Oijala, by a boundary element method without any continuity constraint at the interfaces of the elements,for both the unknowns. We first show how to construct this equation in a simple way, similar tothe usual integral formulations, through imposing to the internal problem related to the Picard system,which is an extension of the Maxwell system, appropriate boundary conditions. For regular geometries, we have established a theoretical background ensuring the stability and the convergence of numerical scheme, by proving that this equation can be decomposed in a coercive elliptic and a compact parts in the context of square integrable functions. Our study was validated by three-dimensional numerical tests. In the case of usual integral equations of the second kind, the theoretical background for smooth surfaces is no longer valid when the surfaces is singular. The formal use of this equation for singular surfaces gave erroneous results. We pointed out the origin of numerical instabilities bydeveloping a two-dimensional version of this equation. This version has allowed us to show that the instabilities were due to parasitic oscillations accumulating on the geometrical singularities. In this context, we have implemented some approaches to reduce this parasitic oscillations on the calculations in the far field.We have shown that the method of increasing the freedom degrees for the charges relatively to the current could significantly reduces these instabilities. As a result, we have implemented this procedure in three-dimensional case. Throughout various tests, we noted the improvement on the approximation brough bay to the stabilization procedure

Стилі APA, Harvard, Vancouver, ISO та ін.

39

Martinho, Lucas Blattner. "Numerical modeling of electromagnetic coupling phenomena in the vicinities of overhead power transmission lines." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/3/3143/tde-28062016-152807/.

Повний текст джерела

Анотація:

Les phénomènes de couplage électromagnétique entre les lignes aé- riennes de transmission d\'énergie et des structures voisines sont inévitables, surtout dans les zones densément peuplées. Les effets indésirables découlants de cette proximité sont variés, allant de l\'établissement des tensions dangereuses à l\'apparition de phénomènes de corrosion dus au courant alternatif. L\'étude de cette classe de problèmes est nécessaire pour assurer la sécurité dans les alentours de la zone d\'interaction et aussi pour préserver l\'intégrité des équipements et des dispositifs présents. Cependant, la modélisation compl ète de ce type d\'application implique la représentation tridimensionnelle de la région d\'intérêt et nécessite des méthodes numériques de calcul de champs spécifiques. Dans ces travaux, des problèmes liés à la circulation de courants électriques dans le sol (ou de couplage dit conductif) seront abordés avec la méthode des éléments finis. D\'autres problèmes résultants de la variation temporelle des champs électromagnétiques (ou de couplage dit inductif) seront aussi considérés et traités avec la méthode PEEC (Partial Element Equivalent Circuit) généralisée. Plus précisément, une condition limite particulière sur le potentiel électrique est proposée pour tronquer le domaine de calcul dans l\'analyse par éléments finis des problèmes de couplage conductif et une formulation PEEC complète pour la modélisation de problèmes de couplage inductif est présentée. Des con gurations tests de complexités croissantes sont considérées pour valider les approches précédentes. Ces travaux visent ainsi à apporter une contribution à la modélisation de cette classe de problèmes, qui tendent à devenir communs avec l\'expansion des réseaux électriques.
Electromagnetic coupling phenomena between overhead power transmission lines and other nearby structures are inevitable, especially in densely populated areas. The undesired effects resulting from this proximity are manifold and range from the establishment of hazardous potentials to the outbreak of alternate current corrosion phenomena. The study of this class of problems is necessary for ensuring security in the vicinities of the interaction zone and also to preserve the integrity of the equipment and of the devices there present. However, the complete modeling of this type of application requires the three- -dimensional representation of the region of interest and needs specific numerical methods for field computation. In this work, the modeling of problems arising from the flow of electrical currents in the ground (the so-called conductive coupling) will be addressed with the finite element method. Those resulting from the time variation of the electromagnetic fields (the so-called inductive coupling) will be considered as well, and they will be treated with the generalized PEEC (Partial Element Equivalent Circuit) method. More specifically, a special boundary condition on the electric potential is proposed for truncating the computational domain in the finite element analysis of conductive coupling problems, and a complete PEEC formulation for modeling inductive coupling problems is presented. Test configurations of increasing complexities are considered for validating the foregoing approaches. These works aim to provide a contribution to the modeling of this class of problems, which tend to become common with the expansion of power grids.

Стилі APA, Harvard, Vancouver, ISO та ін.

40

Martinson, Christiaan Adolph. "Characterisation of a PEM electrolyser using the current interrupt method / Christiaan Adolph Martinson." Thesis, North-West University, 2012. http://hdl.handle.net/10394/8741.

Повний текст джерела

Анотація:

The need to characterise a PEM electrolyser is motivated by a South African hydrogen company. One of two electrochemical characterisation methods, namely the current interrupt method or electrochemical impedance spectroscopy, is investigated to characterise the PEM electrolyser. Various literature sources can be found on the electrochemical characterisation methods. In this study the current interrupt method is used for the electrochemical characterisation of a PEM electrolyser. The current interrupt method is an electrical test method that will be used to obtain an equivalent electric circuit model of the PEM electrolyser. The equivalent electric circuit model relates to various electrochemical characteristics such as the activation losses, the ohmic losses and the concentration losses. Two variants of the current interrupt method, namely the natural voltage response method and the current switching method, are presented. These methods are used to obtain two different equivalent electric circuit models of the PEM electrolyser. The parameters of the first equivalent electric circuit, namely the Randles cell, will be estimated with the natural voltage response method. The parameters of the second equivalent electric circuit, namely the Randles-Warburg cell, will be estimated with the current switching method. Simulation models of the equivalent electric circuits are developed and tested. The simulation models are used to verify and validate the natural voltage response method and the current switching method. The parameters of the Randles cell simulation model is accurately calculated with the natural voltage response method. The parameters of the Randles-Warburg cell simulation model is accurately calculated with the current switching method. The natural voltage response method and the current switching method are also practically implemented. The results is used to indicate the various electrochemical characteristics of the PEM electrolyser. A Nafion 117 type membrane was tested with the current interrupt method. The membrane resistance parameters of Randles cell were estimated with the natural voltage response method. These values are validated with conductivity measurements found in literature. The results of the Randles- Warburg cell is validated with a system identification validation model.
Thesis (MIng (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2013

Стилі APA, Harvard, Vancouver, ISO та ін.

41

Kassir, Wafaa. "Approche probabiliste non gaussienne des charges statiques équivalentes des effets du vent en dynamique des structures à partir de mesures en soufflerie." Thesis, Paris Est, 2017. http://www.theses.fr/2017PESC1116/document.

Повний текст джерела

Анотація:

Afin d'estimer les forces statiques équivalentes du vent, qui produisent les réponses quasi-statiques et dynamiques extrêmes dans les structures soumises au champ de pression instationnaire induit par les effets du vent, une nouvelle méthode probabiliste est proposée. Cette méthode permet de calculer les forces statiques équivalentes du vent pour les structures avec des écoulements aérodynamiques complexes telles que les toitures de stade, pour lesquelles le champ de pression n'est pas gaussien et pour lesquelles la réponse dynamique de la structure ne peut être simplement décrite en utilisant uniquement les premiers modes élastiques (mais nécessitent une bonne représentation des réponses quasi-statiques). Généralement, les mesures en soufflerie du champ de pression instationnaire appliqué à une structure dont la géométrie est complexe ne suffisent pas pour construire une estimation statistiquement convergée des valeurs extrêmes des réponses dynamiques de la structure. Une telle convergence est nécessaire pour l'estimation des forces statiques équivalentes afin de reproduire les réponses dynamiques extrêmes induites par les effets du vent en tenant compte de la non-gaussianité du champ de pression aléatoire instationnaire. Dans ce travail, (1) un générateur de réalisation du champ de pression instationnaire non gaussien est construit en utilisant les réalisations qui sont mesurées dans la soufflerie à couche limite turbulente; ce générateur basé sur une représentation en chaos polynomiaux permet de construire un grand nombre de réalisations indépendantes afin d'obtenir la convergence des statistiques des valeurs extrêmes des réponses dynamiques, (2) un modèle d'ordre réduit avec des termes d'accélération quasi-statique est construit et permet d'accélérer la convergence des réponses dynamiques de la structure en n'utilisant qu'un petit nombre de modes élastiques, (3) une nouvelle méthode probabiliste est proposée pour estimer les forces statiques équivalentes induites par les effets du vent sur des structures complexes décrites par des modèles éléments finis, en préservant le caractère non gaussien et sans introduire le concept d'enveloppes des réponses. L'approche proposée est validée expérimentalement avec une application relativement simple et elle est ensuite appliquée à une structure de toiture de stade pour laquelle des mesures expérimentales de pressions instationnaires ont été effectuées dans la soufflerie à couche limite turbulente
In order to estimate the equivalent static wind loads, which produce the extreme quasi-static and dynamical responses of structures submitted to random unsteady pressure field induced by the wind effects, a new probabilistic method is proposed. This method allows for computing the equivalent static wind loads for structures with complex aerodynamic flows such as stadium roofs, for which the pressure field is non-Gaussian, and for which the dynamical response of the structure cannot simply be described by using only the first elastic modes (but require a good representation of the quasi-static responses). Usually, the wind tunnel measurements of the unsteady pressure field applied to a structure with complex geometry are not sufficient for constructing a statistically converged estimation of the extreme values of the dynamical responses. Such a convergence is necessary for the estimation of the equivalent static loads in order to reproduce the extreme dynamical responses induced by the wind effects taking into account the non-Gaussianity of the random unsteady pressure field. In this work, (1) a generator of realizations of the non-Gaussian unsteady pressure field is constructed by using the realizations that are measured in the boundary layer wind tunnel; this generator based on a polynomial chaos representation allows for generating a large number of independent realizations in order to obtain the convergence of the extreme value statistics of the dynamical responses, (2) a reduced-order model with quasi-static acceleration terms is constructed, which allows for accelerating the convergence of the structural dynamical responses by using only a small number of elastic modes of the structure, (3) a novel probabilistic method is proposed for estimating the equivalent static wind loads induced by the wind effects on complex structures that are described by finite element models, preserving the non-Gaussian property and without introducing the concept of responses envelopes. The proposed approach is experimentally validated with a relatively simple application and is then applied to a stadium roof structure for which experimental measurements of unsteady pressures have been performed in boundary layer wind tunnel

Стилі APA, Harvard, Vancouver, ISO та ін.

42

伊藤, 睦., Atsushi ITOH, Kongkeo PHAMAVANH, 光. 中村, Hikaru NAKAMURA, 忠顕田辺 та Tada-aki TANABE. "格子等価連続体化法による鉄筋コンクリート部材の有限要素解析". 土木学会, 2004. http://hdl.handle.net/2237/8616.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

43

Sevilla, David. "Computerized method for finding the ideal patient-specific location to place an equivalent electric dipole to derive an estimation of the electrical activity of the heart." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2007. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

44

Zhao, Shuo. "Contributions à l'évolution de la méthode de l'onde thermique pour la mesure des charges d'espace dans les structures isolantes pour les câbles HTCC." Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTS025/document.

Повний текст джерела

Анотація:

L'augmentation des besoins en énergie électrique et l'éloignement croissant des lieux de production par rapport aux centres de consommation impulsent le développement du transport d'énergie en courant continu. Dans le cas des câbles haute tension à courant continue (HTCC) à isolation polymère, la problématique de la fiabilité est liée à l'établissement, sous l'effet des fortes contraintes électrothermiques, de zones de charges électriques dans le diélectrique et au niveau des interfaces isolant/compound semi-conducteur. De telles accumulations de charges (dites charges « d'espace » car reparties dans un espace isolant) peuvent faire vieillir prématurément les isolations, voire les faire claquer de manière intempestive. La mise en œuvre de nouveaux matériaux et l’optimisation des structures isolantes pour câbles HTCC nécessitent ainsi le suivi des zones de charges d’espace avec la plus grande précision. Il est alors nécessaire de développer des techniques de mesure non destructives, telle que la méthode de l’onde thermique (MOT), basée sur l’application d’un faible échelon de température à une structure isolante et sur la mesure d’un courant transitoire provoqué par la redistribution des charges d’influence aux électrodes.Ce travail porte sur la faisabilité et la mise en œuvre expérimentale d’une installation, basée sur le principe de la MOT, visant à mesurer les charges d’espace dans des échantillons isolants comportant des couches semi-conductrices, avec une résolution la plus proche possible du degré d’homogénéité des interfaces (de l’ordre du micromètre).Après avoir passé en revue les problématiques des diélectriques soumis à des forts champs continus et les méthodes de mesure de charges d’espace existantes, le mémoire présente divers aspects et grandeurs liés au principe de la MOT, ainsi qu’à la définition et à l’estimation des résolutions spatiales. Des simulations analytiques et numériques sont par la suite menées pour étudier les apports d’une mise en œuvre de la MOT sur des structures isolantes de polyéthylène réticulé chimiquement de 100 µm d’épaisseur avec des électrodes semi-conductrices de 30 µm. Elles montrent que l’application d’échelons de température d’amplitudes n’affectant pas les états électrique et de surface des matériaux se traduit par des signaux de mesure de plusieurs nano ampères pour des variations de champ résiduel de l’ordre du kV/mm par micron. La génération de ces signaux, nécessaires à des mesures ayant une dynamique suffisante et à des résolutions s’approchant du micron, requière des échanges thermiques hautement efficaces entre la source de chaleur (liquide caloporteur) et l’isolant. Une étude par simulation multi-physique bidimensionnelle est réalisée afin d’analyser le transfert de chaleur par contact direct entre un liquide caloporteur et un échantillon-type. Elle permet de définir et d’optimiser une structure innovante de diffuseur thermique et dans laquelle l’échange de chaleur entre le fluide et l’échantillon s’opère par contact direct, assurant ainsi une efficacité bien supérieure aux structures existantes.Le développement d’un outil de mesure par la MOT, basé sur les conclusions des travaux de simulation, est par la suite présentée. Il associe un système hydropneumatique, un diffuseur haute efficacité favorisant la dynamique du transfert thermique et un système de capteurs, en augmentant ainsi l’amplitude des signaux, la reproductibilité et la précision de la mesure. Des mesures d’étalonnage sur des échantillons cibles montrent, par rapport aux résolutions disponibles sur ce type de structure (autour de 10 µm), des améliorations d’un facteur 2 à 5 pour la résolution de positionnement et une résolution de discernement proche de l’état de l’art. L’analyse critique du banc développé, corroborée aux prédictions des simulations, met également en évidence la marge de progression sensible de l’outil, dont les évolutions proposées permettront d’accroître les performances
The increasing needs of electric power and the placement of power plants at more and more remote locations with respect to the users promote the development of electric power transport by DC submarine or terrestrial links. In the case of high voltage direct current (HVDC) cables with polymeric insulation, reliability is strongly affected by the development, under high electrical and thermal stress, of electric charges in the bulk of the dielectric and at the insulator/semiconductor interfaces. These accumulations of charges (called space charges as they are distributed in an insulating space) may lead to premature ageing and breakdown. The setup of new materials and the optimization of insulating structures for HVDC cables require a precise follow-up of the space charge zones. It is therefore necessary to develop non-destructive space charge measurement techniques, as the thermal step method (TSM), which is based on the application of a low temperature step to an insulating structure and on the measurement of a transient current due to the redistribution of influence charges at electrodes.The present work concerns the feasibility and the experimental set up of a device, based on the principle of the TSM, aiming to measure the space charges in insulating samples with semi-conducting electrodes, with a resolution approaching the degree of homogeneity of the interfaces (i.e., of micrometric order).After having reviewed the problematic of the dielectrics subjected to high dc fields and the existing space charge measurement methods, this dissertation presents several aspects and parameters related to the principle of the TSM, as well as to the definition and to the estimation of spatial resolutions. Analytical and numerical simulations are then carried out to study the contributions of a TSM-based setup on insulating structures composed of 100 µm-thick cross-linked polyethylene slabs provided with 30 µm-thick semiconducting electrodes. They show that the application of temperature steps, with amplitudes that do not affect the electrical and surface states of the materials, leads to measurement signals of several nano amperes for variations of the remnant electric field of the order of the kV/mm per micron. Highly effective thermal exchanges between the heat source (heating or coolant liquid) and the insulator are required to generate such signals, needed for measurements of sufficient dynamics and for resolutions approaching the micrometer. A bi-dimensional multi-physics simulation study is made, in order to analyze the heat transfer through a direct contact between the coolant liquid and a sample of the aimed type. The study allows to define and to optimize an innovating structure of thermal diffuser, where the heat exchanges operates by direct contact, thus providing a much better efficiency than the existing structures.The development of a TSM-based measurement tool, using the fallouts of the simulations, is then presented. It associates a hydro pneumatic system, a high efficiency diffuser favoring the dynamics of the thermal transfer and a sensor system, thus increasing the amplitude of the signals, the reproducibility and the accuracy of the measurements. Calibration measurements on the aimed samples show, with respect to the resolutions available on this type of structures (close to 10 µm), enhancements by a factor of 2 to 5 for the positioning resolution an a discerning resolution close to the state of the art. The critical analysis of the developed bench, corroborated to the predictions of the simulations, also puts into focus a significant room for improvement of the tool, for which evolutions proposed in this work would allow to enhance the performance

Стилі APA, Harvard, Vancouver, ISO та ін.

45

Ramli, Khairun N. "Modelling and analysis of complex electromagnetic problems using FDTD subgridding in hybrid computational methods. Development of hybridised Method of Moments, Finite-Difference Time-Domain method and subgridded Finite-Difference Time-Domain method for precise computation of electromagnetic interaction with arbitrarily complex geometries." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5443.

Повний текст джерела

Анотація:

The main objective of this research is to model and analyse complex electromagnetic problems by means of a new hybridised computational technique combining the frequency domain Method of Moments (MoM), Finite-Difference Time-Domain (FDTD) method and a subgridded Finite-Difference Time-Domain (SGFDTD) method. This facilitates a significant advance in the ability to predict electromagnetic absorption in inhomogeneous, anisotropic and lossy dielectric materials irradiated by geometrically intricate sources. The Method of Moments modelling employed a two-dimensional electric surface patch integral formulation solved by independent linear basis function methods in the circumferential and axial directions of the antenna wires. A similar orthogonal basis function is used on the end surface and appropriate attachments with the wire surface are employed to satisfy the requirements of current continuity. The surface current distributions on structures which may include closely spaced parallel wires, such as dipoles, loops and helical antennas are computed. The results are found to be stable and showed good agreement with less comprehensive earlier work by others. The work also investigated the interaction between overhead high voltage transmission lines and underground utility pipelines using the FDTD technique for the whole structure, combined with a subgridding method at points of interest, particularly the pipeline. The induced fields above the pipeline are investigated and analysed. FDTD is based on the solution of Maxwell¿s equations in differential form. It is very useful for modelling complex, inhomogeneous structures. Problems arise when open-region geometries are modelled. However, the Perfectly Matched Layer (PML) concept has been employed to circumvent this difficulty. The establishment of edge elements has greatly improved the performance of this method and the computational burden due to huge numbers of time steps, in the order of tens of millions, has been eased to tens of thousands by employing quasi-static methods. This thesis also illustrates the principle of the equivalent surface boundary employed close to the antenna for MoM-FDTD-SGFDTD hybridisation. It depicts the advantage of using hybrid techniques due to their ability to analyse a system of multiple discrete regions by employing the principle of equivalent sources to excite the coupling surfaces. The method has been applied for modelling human body interaction with a short range RFID antenna to investigate and analyse the near field and far field radiation pattern for which the cumulative distribution function of antenna radiation efficiency is presented. The field distributions of the simulated structures show reasonable and stable results at 900 MHz. This method facilitates deeper investigation of the phenomena in the interaction between electromagnetic fields and human tissues.
Ministry of Higher Education Malaysia and Universiti Tun Hussein Onn Malaysia (UTHM)

Стилі APA, Harvard, Vancouver, ISO та ін.

46

Ramli, Khairun Nidzam. "Modelling and analysis of complex electromagnetic problems using FDTD subgridding in hybrid computational methods : development of hybridised Method of Moments, Finite-Difference Time-Domain method and subgridded Finite-Difference Time-Domain method for precise computation of electromagnetic interaction with arbitrarily complex geometries." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5443.

Повний текст джерела

Анотація:

The main objective of this research is to model and analyse complex electromagnetic problems by means of a new hybridised computational technique combining the frequency domain Method of Moments (MoM), Finite-Difference Time-Domain (FDTD) method and a subgridded Finite-Difference Time-Domain (SGFDTD) method. This facilitates a significant advance in the ability to predict electromagnetic absorption in inhomogeneous, anisotropic and lossy dielectric materials irradiated by geometrically intricate sources. The Method of Moments modelling employed a two-dimensional electric surface patch integral formulation solved by independent linear basis function methods in the circumferential and axial directions of the antenna wires. A similar orthogonal basis function is used on the end surface and appropriate attachments with the wire surface are employed to satisfy the requirements of current continuity. The surface current distributions on structures which may include closely spaced parallel wires, such as dipoles, loops and helical antennas are computed. The results are found to be stable and showed good agreement with less comprehensive earlier work by others. The work also investigated the interaction between overhead high voltage transmission lines and underground utility pipelines using the FDTD technique for the whole structure, combined with a subgridding method at points of interest, particularly the pipeline. The induced fields above the pipeline are investigated and analysed. FDTD is based on the solution of Maxwell's equations in differential form. It is very useful for modelling complex, inhomogeneous structures. Problems arise when open-region geometries are modelled. However, the Perfectly Matched Layer (PML) concept has been employed to circumvent this difficulty. The establishment of edge elements has greatly improved the performance of this method and the computational burden due to huge numbers of time steps, in the order of tens of millions, has been eased to tens of thousands by employing quasi-static methods. This thesis also illustrates the principle of the equivalent surface boundary employed close to the antenna for MoM-FDTD-SGFDTD hybridisation. It depicts the advantage of using hybrid techniques due to their ability to analyse a system of multiple discrete regions by employing the principle of equivalent sources to excite the coupling surfaces. The method has been applied for modelling human body interaction with a short range RFID antenna to investigate and analyse the near field and far field radiation pattern for which the cumulative distribution function of antenna radiation efficiency is presented. The field distributions of the simulated structures show reasonable and stable results at 900 MHz. This method facilitates deeper investigation of the phenomena in the interaction between electromagnetic fields and human tissues.

Стилі APA, Harvard, Vancouver, ISO та ін.

47

Mencarini, Leonardo de Holanda. "Estudo do comportamento de um detector de radiação passivo para fins aeronáuticos utilizando o método Monte Carlo." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/85/85131/tde-07022014-095250/.

Повний текст джерела

Анотація:

Profissionais da área aeronáutica, como pilotos e comissários de bordo, são submetidos a doses de radiação de origem cósmica, que podem ser maiores do que as doses médias dos trabalhadores da indústria nuclear. A diversidade de partículas de altas energias presentes no campo de radiação a bordo das aeronaves torna complexa a mensuração da dose e requer cuidados especiais em relação aos sistemas de dosimetria a serem empregados nesta área. A Força Aérea Brasileira, por meio de seu Instituto de Estudos Avançados (IEAv /DCTA), em conjunto com o Instituto de Pesquisas Energéticas e Nucleares (IPEN / CNEN -SP) vem estudando o assunto desde 2008. Um protótipo de detector de radiação passivo para medições em aeronaves foi previamente construído e testado em condições de voo e de laboratório. O detector é capaz de medir a grandeza dosimétrica conhecida como dose absorvida (usando dosímetros passivos), que serão posteriormente correlacionados ao equivalente de dose ambiente e à dose efetiva recebidos por profissionais da área aeronáutica. Neste contexto, uma abordagem teórica por meio de simulações Monte Carlo com os códigos computacionais MCNP5 e MCNPX, foi usada para modelar e caracterizar a resposta do detector em determinadas condições experimentais. Este trabalho apresenta os resultados preliminares da modelagem computacional, com ênfase especial na comparação entre a grandeza fundamental dose absorvida (mensurada e simulada) e sua relação com o equivalente de dose ambiente e dose efetiva para este detector.
Aircrews, as pilots and flight attendants, are subjected to cosmic ray doses which can be higher than the average doses on workers from the nuclear industry. The diversity of particles of high energies present in the radiation field on board of aircrafts, turns the determination of the incident dose and requires special care regarding dosimetric systems to be used in this kind of field. The Brazilian Air Force, through the Institute for Advanced Studies (Instituto de Estudos Avançados, IEAv/DCTA) in conjunction with the Institute of Energetic and Nuclear Research (Instituto de Pesquisas Energéticas e Nucleares IPEN/CNEN-SP) are working on this subject since 2008. A prototype of a radiation detector for aircraft measurements was previously built and tested in flight and laboratory conditions. The detector is able of measuring a quantity known as absorbed dose (using passive dosimeters), which will subsequently be correlated to the ambient dose equivalent and the effective dose received by aircrews. In this context, a theoretical approach through Monte Carlo simulations with the computational codes MCNP5 and MCNPX was used to model and characterize the detector response at such experimental conditions. This work presents the preliminary results of the computational modeling, with special emphasis on the comparison between the absorbed dose quantity (measured and simulated) and its relationship with the ambient dose equivalent and the effective Dose for this detector.

Стилі APA, Harvard, Vancouver, ISO та ін.

48

Tian, Feng. "A comparison of equating/linking using the Stocking-Lord method and concurrent calibration with mixed-format tests in the non-equivalent groups common-item design under IRT." Thesis, Boston College, 2011. http://hdl.handle.net/2345/2370.

Повний текст джерела

Анотація:

Thesis advisor: Larry Ludlow
There has been a steady increase in the use of mixed-format tests, that is, tests consisting of both multiple-choice items and constructed-response items in both classroom and large-scale assessments. This calls for appropriate equating methods for such tests. As Item Response Theory (IRT) has rapidly become mainstream as the theoretical basis for measurement, different equating methods under IRT have also been developed. This study investigated the performances of two IRT equating methods using simulated data: linking following separate calibration (the Stocking-Lord method) and the concurrent calibration. The findings from this study show that the concurrent calibration method generally performs better in recovering the item parameters and more importantly, the concurrent calibration method produces more accurate estimated scores than linking following separate calibration. Limitations and directions for future research are discussed
Thesis (PhD) — Boston College, 2011
Submitted to: Boston College. Lynch School of Education
Discipline: Educational Research, Measurement, and Evaluation

Стилі APA, Harvard, Vancouver, ISO та ін.

49

Li, Yong-Xiu, and 李永秀. "Equivalent Linear Method using Statistics and Optimization." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/84627999981474239405.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

50

Pon, Jyun-Jie, and 彭俊傑. "Quantum-Mechanic Simulation using Equivalent-Circuit Method and k-matrix Method." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/43b57c.

Повний текст джерела

Анотація:

碩士
國立中央大學
電機工程研究所
94
In the thesis, we will use two methods to simulate the quantum mechanical systems. The first way is called the k-matrix method, and the other way is the equivalent-circuit method. We use these two methods to analyze periodic KP-model and non-periodic QM systems. The result obtained by these ways is the wave function of the Schrödinger wave equation. Additionally, we will compare the k-matrix method with the equivalent-circuit method and show these results of the k-matrix method are same as the equivalent-circuit method. We will also show the advantages and disadvantages of these two methods.

Стилі APA, Harvard, Vancouver, ISO та ін.

Дисертації з теми "Method of equivalent charges"

Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями