Navegando por Orientadores "OLIVEIRA, Rodrigo Melo e Silva de"

Agora exibindo 1 - 16 de 16

Acesso aberto (Open Access)
Antenas de grafeno com controle de diagrama de radiação: projeto e modelagem via método FDTD
(Universidade Federal do Pará, 2015-08-28) RODRIGUES, Nilton Rodolfo Nascimento Melo; DMITRIEV, Victor Alexandrovich; http://lattes.cnpq.br/0684541646225359; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
In this work, it is developed a mathematical formulation for modelling Graphene sheets in the three-dimensional lattice used to solve Maxwell’s equations with Yee’s algorithm. The technique is based on piecewise linear recursive convolution method and on thin material sheets technique, valid in intraband range. The HFSS software is used for to designing, for the first time, graphene antennas with dynamic control of the radiation pattern main lobe by tuning the chemical potential of graphene sheets used as passive elements. The numerical method developed in this work fully agrees with the results obtained by using HFSS (this one is based on the Finite Element Method).
Acesso aberto (Open Access)
Atenuação de oscilações magnetohidrodinâmicas em cuba de redução de alumínio usando estruturas periódica
(Universidade Federal do Pará, 2023-04-27) ANDERE, Thais Pascoal de Oliveira; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
Magnetohydrodynamic instability (MHD) in an aluminum reduction cell is due to the interactions between the conductive liquid currents and the magnetic field generated by very high currents flowing through current feeding circuit buses. Such phenomenon creates oscillations in this fluid, compromising the efficiency of the process aluminum reduction. The reduction cells consist, in their usual configuration, of a container with flat walls that accommodates the liquid. In this work, a new geometry is proposed for the container based on periodic structures, with the aim of to mitigate such oscillations. The analysis of oscillations of fluid in both configurations is made with a software developed in this work to numerically simulate the process in two dimensions. The numerical formulation employed is based on the finite-difference time-domain method to solve the Navier-Stokes equations (N-S) explicitly through the Chorin projections method. The volume and surface of the fluid are mapped using the MAC method, (marker and cell). The liquid is treated as incompressible and viscous, in addition to being electrically conductive. The accelerations caused by magnetic field and the electric currents are coupled to N-S by calculating the Lorentz Force. The results are analyzed and comparisons through the difference between the variation of the height of the conductive fluid in two scenarios, considering the flat bottom of the cell, current configuration, and by applying periodic structures at the bottom of the cell.
Acesso aberto (Open Access)
Desenvolvimento de Interface gráfica como suporte para soluções numéricas das equações de Maxwell em coordenadas gerais – 3D
(Universidade Federal do Pará, 2011-05-03) COLARES, Adolfo Francesco de Oliveira; SOUZA SOBRINHO, Carlos Leônidas da Silva; http://lattes.cnpq.br/1450994881555781; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
In this work, we have implemented a graphical user interface (GUI) by using the Nokia Qt library (version 3.0). The interface is designed to simplify the creation of scenarios for executing parallel E.M. Simulations by using the numerical technique Local Non-Orthogonal Finite Difference Time-Domain (LN-FDTD) method, applied to solve Maxwell's equations. The simulator was developed by using the C programming language and parallelized by using threads. This way, the pthread library was employed. The 3D visualization of the scenario and of the corresponding mesh to be simulated is performed by a specially developed program based on the OpenGL specification. In order to improve the development and to achieve the goals of computational design, we have used concepts of software engineering, such as the process model for software prototyping. Depriving the user to interact directly with the source code of the simulation program, the probability of human errors while performing the constructing process of scenarios is minimized. In order to demonstrate the operation of the developed tool, a study regarding lightning-induced voltages on low voltage lines with catenaries is performed. Induced voltages inside a small building (a residence) are also studied.
Acesso aberto (Open Access)
Desenvolvimento de metodologias automáticas para obtenção do parâmetro de forma ótimo para o método RPIM
(Universidade Federal do Pará, 2012-12-21) MACHADO, Péricles Lopes; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
In this thesis, a methodology is proposed for automatically (and locally) obtaining the shape factor c for the Gaussian basis functions, for each support domain, in order to increase numerical precision and mainly to avoid matrix inversion impossibilities. The concept of calibration function is introduced, which is used for obtaining c. The methodology developed was applied for a 2-D numerical experiment, which results are compared to analytical solution. This comparison revels that the results associated to the developed methodology are very close to the analytical solution for the entire bandwidth of the excitation pulse. The proposed methodology is called in this work Local Shape Factor Calibration Method (LSFCM).
Acesso aberto (Open Access)
Desenvolvimento e implementação da técnica Electric Charge Gaussian Gradation Method (ECGGM) aplicada ao Método Radial de Interpolação por Pontos (RPIM) com Truncagem ADE-PML
(Universidade Federal do Pará, 2016-08-19) BRANDÃO, Marcelo Brazão e Silva; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
In this work, an improved meshless discretization methodology, based on the Coulomb's Law Discretization Method (CLDM), is introduced. With the presented improvement, it is possible to controllably increase the density of nodes around edges and corners of metallic scatterers immersed in analysis space in a natural way by gradually modifying node's charges using Gaussian functions. Also, a new computational implementation of ADE-PML (Auxiliary Differential Equation - Perfectly Matched Layer) to truncate the method meshless RPIM is presented. The equations used in the absorbent region are obtained in the time domain using auxiliary differential equations, then the developed formulation is validated through numerical experiments related to the reflection error of absorbent material and also by calculating the radar cross section (RCS) of a metal cylindrical scatterer, which has a known analytical solution. It is observed that higher concentration of nodes on the neighborhood of media interfaces substantially improves the precision of numerical solutions of Maxwell's equations obtained with the Radial Point Interpolaton Method (RPIM) because of the proper calculation of fields near the boundaries. Several other relevant benefits resulting from the new technique are observed and highlighted. The proposed ADE-PML formulation produces free field update equations of so-called split fields characteristic of the original PML. Recursive convolution used by CPML (Convolutional Perfectly Matched Layer) are not used, avoiding problems of absorption when small time steps are employed.
Acesso aberto (Open Access)
Desenvolvimento e implementação de gerador de surto e sua aplicação na análise numérico-experimental do comportamento transitório de sistemas de aterramento elétrico.
(Universidade Federal do Pará, 2015-09-21) ARAÚJO, Ramon Cristian Fernandes; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
In this work, the design and construction steps of a voltage surge generator are detailed based on established international standards (IEC 61000-4-5). The waveforms of the two output signals implemented are representative of surges due to the first and subsequent lightning strokes, respectively. Also, their parameters meet the requirements imposed by the standards IEC 60060-1 and IEEE Std-4. In order to validate the surge generator, it was analyzed the transient and steady-state behaviors of several grounding systems when subjected to lightning strokes, using the developed generator as the source of the injection signal. The grounding systems were analyzed by field experiments, and each experiment was reproduced numerically using the FDTD method. Low percentage errors were obtained between the signals measured during the field experiments and the corresponding numerical signals. Moreover, the analyzed grounding systems behaved as expected in literature. Those two facts validade the surge generator built in this work.
Acesso aberto (Open Access)
Detecção e localização de descargas parciais em transformadores de potência utilizando sinais acústicoas transitórios e o método GSPS
(Universidade Federal do Pará, 2015-01-29) ARAÚJO, José Weliton de Oliveira; FARIAS, Rubem Gonçalves; http://lattes.cnpq.br/3261608243924147; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
In this work, we develop a method for locating partial discharges (PDs), in power transformers, based on GPS (Global Positioning System) algorithm. For analyzing the structure, we implement a software in which the di erential equations that describe the propagation of acoustic waves are solved numerically by the Acoustic Finite-Di erence Time-Domain (AFDTD) method. The AFDTD computational domain is truncated by the CPML technique (Convolutional Perfectly Matched Layer). The obtained results are compared to estimates produced using electromagnetic waves generated by PDs.
Acesso aberto (Open Access)
Estudo experimental de transitórios eletromagnéticos em sistemas de aterramento elétrico devidos a pulsos de descargas atmosféricas
(Universidade Federal do Pará, 2015-05-29) CARVALHO, Lorena de Fátima Pinheiro de; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/1450994881555781
In this dissertation, we present a study on the transient and steady-state behaviors of grounding systems when subjected to surges with the waveform of a lightning discharge. The analyses of grounding systems were made using data obtained through experiments conducted in the field and numerical simulations based on the finite-difference method applied to solve Maxwell’s equations in the time domain. In numerical simulations, the experimental setup (rods, cables, resistor and injected signal) and the electromagnetic parameters (conductivity, permittivity and magnetic permeability) of soil and vacuum were modeled numerically. There was good agreement between the measured signals during the experimental tests and their respective signals obtained numerically. This agreement between measured and simulated transient signals was obtained by taking certain technical precautions when designing the experimental setup. Such technical precautions, which are usually not explicitly mentioned in technical literature, are properly addressed and discussed in this dissertation.
Acesso aberto (Open Access)
Método espectral para localização de múltiplas descargas parciais na parte dielétrica de bobinas de hidrogeradores
(Universidade Federal do Pará, 2014-08-18) MODESTO, Jonathas Felippe Morais; DMITRIEV, Victor; http://lattes.cnpq.br/3139536479960191; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
A methodology based on spectral analysis is established for performing localization of multiple partial discharges in dielectric region of hydro-generators coils. This pinpointing of multiple discharges aims to provide means for performing preventive diagnosis of the insulating region of the referred coil. A computer model of the structure was conceived by using the finite-difference time-domain method (FDTD-3D) to numerically solve Maxwell’s equations, which is experimentally validated. The transient electric field associated with partial discharges that occur at different positions of the coil is calculated and its spectrum, after processing and statistical analysis, is used to perform the diagnosis. In approximately 90% of simulations, accurate estimates of simultaneous discharges location were obtained. Transient numerical results are in agreement with literatures measurements performed experimentally. A new method of injection of partial discharge signals was also developed in this work.
Acesso aberto (Open Access)
Um método para modelagem numérica plena da dispersão elétrica do solo usando aproximadores de padé e o método das diferenças finitas no domínio do tempo
(Universidade Federal do Pará, 2016-02-29) NASCIMENTO, Júlio Antônio Salheb do; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
In this dissertation, it is developed and implemented a numerical method for modeling the soil electrical dispersion using the Finite-Dierence Time-Domain method (FDTD). The methodology is based on the application of Padé approximants in frequency domain, in such a way to represent the spectral dependency of soil's conductivity and electrical permittivity. The time domain equations are obtained using simple algebraic operations and inverse Fourier transforms. Experimental results for grounding systems subjected to articial lightning pulses are compared with numerical results obtained using the proposed method. It was observed an excellent agreement between the corresponding transient signals.
Acesso aberto (Open Access)
Metodologia de discretização espacial para o método radial de interpolação por pontos (RPIM) aplicada para solução numérica das equações de Maxwell
(Universidade Federal do Pará, 2013-03-04) SOUSA, Washington César Braga de; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
In this work, a new method, based on Coulomb's Law, has been developed and computationally implemented for performing spatial discretization for meshless methods. The new methodology, named Coulomb Law Discretization Method (CLDM), employs an adapted version of the Coulomb's vector force equation for obtaining a balanced distribution of nodes in space, in such way to achieve high discretization quality for the node set. The Radial Point Interpolation Method (RPIM) and the Uniaxial Perfectly Matched Layers (UPML) are used for solving Maxwell's Equations in time domain for 2D problems (TMz mode).
Acesso aberto (Open Access)
Metodologias de discretização espacial sem malha baseadas nos potenciais de Coulomb e Lennard-Jones para o método radial de interpolação por pontos (RPIM) aplicadas para solução numérica das equações de Maxwell
(Universidade Federal do Pará, 2017-12-04) SOUSA, Washington César Braga de; RABELO, Wilson Ricardo Matos; http://lattes.cnpq.br/7978676206209168; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
In this thesis, three new particle interaction methods based on the Coulomb's and Lennard- Jones' potentials have been developed (and computationally implemented), aiming to generate meshless spatial discretization which can be used to the Radial Point Interpolation Method (RPIM) for solving partial di erential equations. These new methods, called Coulomb Law Discretization Method (CLDM), Electric Charge Gaussian Gradation Method (ECGGM) e Lennard-Jones Discretization Method (LJDM),employ adapted versions of Coulomb's and Lennard-Jones' vector forces equations for obtaining a balanced distribution of nodes in space (equilibrium state), in order to achieve high discretization quality of space and complex structures. For this aim, a new quality metrics is introduced. This doctoral thesis is presented as an aggregation of three scienti c papers, which present respectively the methods: CLDM, ECGGM and LJDM. The RPIM and the uniaxial perfectly matched layers (UPML) are used for solving Maxwell's equations in time domain for 2D (TMz mode) and 3D problems. The CLDM, ECGGM and LJDM methods (each in conjunction with the RPIM method) are applied to electromagnetic scattering problems, based on circular, elliptic and triangular metal cylinders (2D case). The LJDM / RPIM method is applied to the 3D case. The obtained results are in accordance with analytical solutions.
Acesso aberto (Open Access)
Modelagem através do método das diferenças finitas no domínio do tempo (FDTP) de solos dispersivos utilizando aproximações de Padé validada com experimentos em campo
(Universidade Federal do Pará, 2015-08-31) FUJIYOSHI, Daiyuki Maia; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
The Amazonian soil of Belém is modeled as a dispersive material, of which the electrical conductivity is dependent on the frequency. For this aim, we use the Padé's approxima-tion in frequency domain, which is applied to Ampère's law. Special update equations for electric field in time domain are obtained by applying time averaging and the in-verse Fourier transform. The results obtained by numerical simulations performed with the FDTD method are compared to transient responses measured in field. Lightning-patterned pulses are injected in classical grounding systems. Excellent agreement is ob-served, which validates the developed numerical method.
Acesso aberto (Open Access)
Superfície seletiva de frequências inteligente baseada em grafeno
(Universidade Federal do Pará, 2019-09-02) PAIVA, Rodrigo Rodrigues; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
In this work, a formulation based on the finite-difference time-domain (FDTD) and on the exponential matrix methods is developed for modeling thin graphene sheets. This formulation is validated by reproducing problems involving graphene frequency selective surfaces (FSS) known from literature. Then, we propose in this work a smart graphene FSS device. Smartness is obtained by means of a unity cell formed by a graphene ring with a graphene sheet placed in its aperture. By properly regulating the chemical potentials of the graphene elements, two frequency-tunable modus operandi are obtained: single- or dual-band rejection modes. When the device operates in its dual-band rejection mode, either of the rejection bands can be shifted individually in the frequency spectrum. Additionally, both rejection bands can also be reconfigured simultaneously. With the device operating in single-band rejection mode, it is also possible to shift its rejection band in the frequency spectrum.
Acesso aberto (Open Access)
Técnica semiautomática de rotulagem e sistema para geração artificial de PRPDs aplicados ao treinamento de classificador de descargas parciais em hidrogeradores
(Universidade Federal do Pará, 2024-02-29) LOPES, Frederico Henrique do Rosário; ZAMPOLO, Ronaldo de Freitas; http://lattes.cnpq.br/9088524620828017; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
Hydrogenerators are crucial assets for both power generating companies and the population that relies on this supply. However, these machines are susceptible to various types of defects that can result in unexpected interruptions if nothing is done about it. Partial discharge analysis is an already established approach for assessing the condition of high-voltage equipment, with the automatic detection of different types of defects being essential, since different levels of risk to operation vary according to the type of discharge. Deep neural networks have been proposed aiming at the classification of partial discharges using phase-resolved partial discharge (PRPD) diagrams. However, obtaining labeled datasets with a large number of examples is a problem that directly impacts the performance of supervised trained classifiers. In this context, this dissertation proposes a semi-automatic technique for PRPD labeling, based on dimensionality reduction strategies and data clustering, as well as investigates the use of Generative Adversarial Networks (GANs) in artificially expanding the training set. The dataset used in the work consists of real PRPDs obtained through online monitoring procedures of partial discharges in hydrogenerators. The performance of the proposed systems is contrasted with recent representative results from the state-of-the-art in the field. The results demonstrate that the application of the proposed semi-automatic labeling technique has the potential to considerably reduce the workload and time associated with manual classification. Furthermore, the use of artificial PRPDs generated by GANs resulted in a notable improvement in the classifier’s performance, reaching an average accuracy of 94.72%, compared to 89.44% obtained with the best competing technique. Similar gains were also observed in class accuracies.
Acesso aberto (Open Access)
Transporte de ozônio em hidrogerador de 311 mva: modelagem fluidodinâmica tridimensional de máquina elétrica dos elementos finitos. através do método
(Universidade Federal do Pará, 2024-02-29) GIROTTO, Gustavo Gaspar; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
In this work, a three-dimensional numerical model of fluid dynamics is developed for a single 311 MVA power generator unit in a hydroelectric power plant using the finite element method. The goal is to study the ozone transport mechanisms within the enclosed structure of the electrical generator machine. Ozone is produced by partial discharges related to some faults in the stationary bars. To analyze the ozone transport from localized sources, a three-dimensional fluid dynamics model of an operational hydrogenerator is developed and presented for the first time. The model has a high level of geometric details. Additionally, a new proposal to simplify the modeling of radiators is implemented and validated. The modeled structure is based on an electrical machine from the Campos Novos hydrogenerator and consists of 378 coil-type stationary bars made of mica-coated copper and, externally, by a layer of semiconductor coating. Other parts are also represented, including the stationary core and air deflectors made of stainless steel, copper radiators, the rotor with its epoxy surface, and the floor and external walls made of concrete. In the fluid dynamics model, a finite element mesh is designed to represent the air regions inside the hydrogenerator and the surfaces of materials reacting with ozone (with their respective reaction rates), where air flow and ozone transport are modeled using the Navier-Stokes equations and the law of mass conservation. Partial discharge sources are represented by ozone sources with prismatic shapes, positioned on the surfaces of stationary bars. Ozone concentrations are calculated inside and around the generator machine. The rotor radius is 3.8075 m, and its rotation frequency is 200 RPM. The radial air velocity due to interpolar ventilation is also considered (2.2 m/s, as experimentally verified on-site). The radial velocity near the radiators is 3 m/s. It is concluded that the ozone transport profile is influenced by the source position on the stationary bars, so determining the source location is possible and depends on determining the local and global maximum ozone concentration areas on the radiators.