Navegando por Assunto "Eletromagnetismo"

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Acesso aberto (Open Access)
An automatic methodology for obtaining optimum shape factors for the radial point interpolation method
(2011-12) MACHADO, Péricles Lopes; OLIVEIRA, Rodrigo Melo e Silva de; SOUZA, Washington César Braga de; ARAÚJO, Ramon Cristian Fernandes; TOSTES, Maria Emília de Lima; GONÇALVES, Cláudio
In this letter, 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)
Análise de esforços eletromagneto-mecânicos nos enrolamentos de um transformador sob condições de correntes de inrush
(Universidade Federal do Pará, 2016-04-27) FONSECA, Wellington da Silva; SOEIRO, Newton Sure; http://lattes.cnpq.br/7303174583088137; NUNES, Marcus Vinícius Alves; http://lattes.cnpq.br/9533143193581447
This thesis presents an analysis of the effect of electromagnetic origin forces on structural deformation, stress and safety factor in power transformers when they are subjected to inrush currents. The methodology adopted is based on a magneto-mechanical assessment of the transformer using the finite element method (FEM). In this sense, the operating condition of its transformer energization is considered to accurately estimate the magnetic field density in the ferromagnetic structure and to find the values of mechanical stresses or forces in the axial and radial directions on the windings. These components are distributed over energized the high-voltage windings for observing the mechanical loading, which are more susceptible to such current actions. With this goal, it is implemented two- dimensional (2D) and threedimensional (3D) modeling of the discretized transformer structures in consolidated software, which are based on the Finite Elements Method, intended so to obtain more precise results in calculating the variables described. Comparisons between the results from the numerical method with those obtained by analytical methods are made, demonstrating that the FEM provides more precise distribution of stresses along the windings of the transformers when subjected to operating limits conditions as under currents inrush. It is also presented the magnetic flux distribution in the transformer, with high currents circulating in concentric winding of this. It modifies the flux path, causing in a significant increase in the leakage field and consequently on radial and axial forces. The results obtained for the structural behavior of the windings during inrush currents were also seen that the ends of the windings, where the spacers are located, producing high structural weakness due to the axial electromagnetic forces. This also implies a reduction in the safety factor at the ends windings ends and should be considered on the design of power transformers.
Acesso aberto (Open Access)
Análise de metodologia baseada no sistema de ensino individualizado de Keller aplicada em um curso introdutório de eletromagnetismo
(2011-03) ALVES, Danilo Teixeira; SOUZA, Sandro Aléssio Vidal de; PEREIRA FILHO, Silvio Carlos Ferreira; ELIAS, Walace de Sousa
One of individualized teaching methods used and documented in the 70's was Fred Keller's Personalized System of Instruction (PSI). Several papers about this methodology were published, providing an extensive empirical evidence of PSI's positive results. Nonetheless its employment has declined staring in the 80's. Among the reasons for this decline, we may emphasize the greater effort required to the development of such courses using this methodology as compared to other methodologies and the provisioning of a systematic feedback on students' performance, as well as the criticisms on Keller's behaviorist approach. Despite being critical to learning, the stimulus to student's active posture, respect for individual learning rhythm, the formative assessments and the provisioning of systematic feedback to students still take place outside the classroom. One strategy to counter such deficiencies is individualized instruction. In this paper, we propose several modifications to Keller's SPI seeking a feasible methodology to be applied in an introductory course of electromagnetism for students of Physics of Universidade Federal do Pará. Among these modifications, we highlight: (i) the use of weekly assessments, but not in every lecture; (ii) the correction of assessments and feedback providing made by teachers and not teaching assistants; and (iii) the partial maintenance of the expositive classes. Despite the modifications inserted, based on an evaluation which included measurable benchmarks, we have indications that the application of this methodology yielded several of those positive results common to the implementation of Keller's SPI.
Acesso aberto (Open Access)
Análise de metodologia baseada no sistema personalizado de instrução num curso introdutório de eletromagnetismo
(Universidade Federal do Pará, 2009-02-18) SOUZA, Sandro Aléssio Vidal de; ALVES, Danilo Teixeira; http://lattes.cnpq.br/6642002445572793
Despite being essential for apprenticeship, the stimulus to the student’s active posture (versus the listener’s one), the respect to the individual learning pace, the formative evaluations and the supply of systematic feedback to the student are frequently outside the classrooms in schools and colleges. A strategy to bring such characteristics to the classrooms is through individualized teaching. One of the individualized teaching procedures most documented and applied is Fred S. Keller’s Personalized System of Instruction (PSI). Intensively used in the 70‟s, thousands of articles were published about PSI, giving vast empirical evidence about its results, which, in general, is superior to other forms of teaching. In spite of that, the application of this method began to decline in the 80‟s. Among the reasons for that, it’s possible to highlight the amount of initial efforts that were necessary to build a course based on the PSI, the possible resistance from teachers and educators due to the change in the teacher’s role from knowledge transmitter to advisor and the necessary logistics to provide a systematic feedback to students. It’s also worth to emphasize that, independently from which factors contributed to the decline in the usage of PSI, its efficiency is unquestionable. At the present work, an individualized teaching methodology based on the PSI was analyzed and experimented in an introductory course of electromagnetism for Physics students at the third college semester at the Federal University of Pará (Brazil). This methodology employed some of the characteristics of the PSI, respecting the features of the subject like the presence of long calculations and absence of tutors. There was evidence that, despite the introduced modifications, the application of the methodology may bring many of the positive results obtained with the application of the PSI.
Acesso aberto (Open Access)
Decomposição em valores singulares aplicada a dados de campo magnético
(Universidade Federal do Pará, 1992-12-15) MOURA, Helyelson Paredes; O'BRIEN, Douglas Patrick
The singular value decomposition of a matrix A, n x m, which represents a magnetic anomaly, can be seen as a bidimensional coherence filtering method which separates the correlated information from noncorrelated information in a magnetic data matrix A. The filter is defined by expansion of matrix A into eigenimages and singular values. Each eigenimage is constructed by the scalar product of the base vectors and eigenvectors, which are associated with the eigenvectors and eigenvalues of the covariance matrices ATA and AAT. This filtering method is based on the fact that the eigenimages, which are associated with large singular values, concentrate the major part of the correlated information present in the data, while the noncorrelated part, including noise caused by external magnetic sources, compilation errors, and shallow magnetic sources comprise the remaining eigenimages. This method was employed on many examples of synthetic and real data from PETROBRÁS' Carauari-Norte project (Solimões Basin) in order to investigate the utility of the method in the identification, elimination and attenuation of noise present on magnetic data and as a possible method for enhancing certain features generated by anomalies of shallow and deep origin. This work suggests the desirability of introducing both static and dynamic shift on magnetic lines to enhance the correlation (coherence) between the magnetic lines. This shift concentrates the correlated signal in the first few eigenimages. Another important aspect of this decomposition into eigenimages and eigenvalues is the savings gained in storage of a matrix A of n x m units. Memory requerements can be diminished considerably by using p autoimages, i. e. p x (n + m + 1) units without altering the form of the anomaly. We conclude that an appropriate choice of eigenimages generated by SVD decomposition shows good promise as a processing method in magnetic data.
Acesso aberto (Open Access)
DesG: uma nova metodologia para intervenção e coleta de dados magnetotelúricos
(Universidade Federal do Pará, 2006-08-29) SILVA, Lúcia Maria da Costa e; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491
This thesis presents two contributions to magnetotelluric data interpretation. The first one is a new MT inversion method, named Geologic-Descriptive Method (DesG) because it explicitly incorporates a priori information, keeping a close correspondence with the standard description of geological features. The user defines by means of geometric elements (points and axes) the skeleton of geological features, and establishes a priori values for the resistivity of the assumed geological bodies. The method estimates the resistivity distribution in the subsurface, which are closest to the specified geometric elements and produce an acceptable fit to the observations. The analysis of an obtained solution may help in modifying the a priori outline for the sources, allowing, in this way, that successive inversions be performed until the solution fit the data and make geological sense. Among the attractive features of the presented method are: (i) the anomalous sources may present a resistivity larger or smaller than the resistivity of the host rocks, (ii) several host rocks, enclosing or not anomalous sources, may be crossed by the traverse, and (iii) the resistivity contrast between the anomalous source and the host rock may be either abrupt or gradational. Tests on synthetic data reveal, among other relevant features, excellent results in estimating the attitudes of variable-dip faults, which are of particular importance in regional tectonic studies, and in delineating diabase sills within sedimentary basins, which represent a severe obstacle in oil prospecting. The method also allows the joint interpretation of the target sources and the sources causing static shift. Tests using data from COPROD2 shows a estimative of the resistivity distribution in agreement with the geological knowledge about the area. The second contribution relates to the design of geophysical experiment. By means of several indicators, particularly the density information matrix, it is shown that one can access the theoretical resolution of the data, which guides the explorationist in carrying out a survey design. The survey design optimization allows determining the most suitable observation locations and periods to produce a more precise delineation of sources, whose locations are approximately known.
Acesso aberto (Open Access)
Estudo de secagem por microondas e eólica-solar térmica
(Universidade Federal do Pará, 2003-04-29) PAIVA, Reginaldo Sabóia de; MACÊDO, Emanuel Negrão; http://lattes.cnpq.br/8718370108324505; PINHO, João Tavares; http://lattes.cnpq.br/0847897516772421
With the main objective of studying and developing methodologies of control and simulation of microwave drying processes, this work uses as tool the physical-mathematical modelling of the thermal effects and mass transfer caused by microwave radiation in porous solid materials, taking into account the important variables for each case. Several results are presented, such as simulations of electric field profiles, power density, temperature and humidity inside materials with homogeneous characteristics and with simple geometry for the one, two and three-dimensional excitations. As a complementary study, the thermal process for the sizing of solar and wind dryers is modeled including the presentation of the results of the simulations developed.
Acesso aberto (Open Access)
Métodos geofísicos aplicados a prospecção mineral na região do Igarapé Chega Tudo, Maranhão - Brasil
(Universidade Federal do Pará, 1982-12-29) ORTEGA GONZALEZ, Moisés; RIJO, Luiz; http://lattes.cnpq.br/3148365912720676
This work of geophysical prospecting was carried out on a NW-SE geological lineament zone from Chatão - on the right side of Gurupi river up to 5 km beyond Chega Tudo in the State of Maranhão. The field work with the application of magnetic (total field), radiometric, electroresistivity (Schlumberger, Wenner and Half-Schlumbergere) and EM (Sligram) methods was carried out in two stages: a) reconnaissance survey of a 22 km2 area with magnetic and radiometric methods, and b) detailed survey of a 3.5 km2 area with electroresistivity and EM methods. The objectives were to study the main geoelectrical structures associated with mineralized zones, and to select among the used geophysical techniques the one with greater resolution to locate sub-surface quartz veins with gold mineralization. The magnetic method shows a large anomaly in the NE region of the area of reconnaissance, whereas the radiometric method indicates only the background value everywhere. Therefore the latter will be not discussed. The electroresistivity and EM surveys indicate many important anomalies on the detailed area. The electroresistivity and magnetic interpretation were carried out by computacional techniques whereas the EM data were interpreted by phase diagrams. The results show a good correlation between the magnetic and electroresistivity anomalies and the mineralized zone. The EM method was not found effective because it could not discriminate the anomalies inside and outside the mineralized zone. All anomalies were tested with well logs. Since the studied area has the same degree of difficulties for geological prospecting as any other similar area in the Amazon region, the results presented here show that the magnetic and electroresistivity methods, which turned out to be very effective as exploration tools for prospecting gold at Chega Tudo region, could be applied to any other environment with similar geological characteristics.