Análise de estruturas de superfície delgadas axissimétricas via método dos elementos finitos com utilização de elemento retilíneo

The present work deals with the linear analysis of bi-dimensional axisymmetric structures, through development and implementation of a Finite Element Method code. The structures are initially studied alone and afterwards compatibilized into coupled structures, that is, assemblages, including tanks and pressure vessels. Examples are analysed and, in order to prove accuracy, the results were compared with those furnished by the analytical solutions

Análise não-linear de treliças pelo método dos elementos finitos posicional

This work presents the positional nonlinear geometric formulation for trusses using different strain measures. The positional formulation presents an alternative approach for nonlinear problems. This formulation considers nodal positions as variables of the nonlinear system instead of displacements (widely found in literature). The work also describes the arc-length method used for tracing equilibrium paths with snap-through and snap-back. Numerical applications for trusses already established in the literature and comparisons with other studies are provided to prove the accuracy of the proposed formulation

Método dinâmico aplicado para antenas cilíndricas

Nowadays there has been a major breakthrough in the aerospace area, with regard to rocket launches to research, experiments, telemetry system, remote sensing, radar system (tracking and monitoring), satellite communications system and insertion of satellites in orbit. This work aims at the application of a circular cylindrical microstrip antenna, ring type, and other cylindrical rectangular in structure of a rocket or missile to obtain telemetry data, operating in the range of 2 to 4 GHz, in S-band. Throughout this was developed just the theoretical analysis of the Transverse transmission line method which is a method of rigorous analysis in spectral domain, for use in rockets and missiles. This analyzes the spread in the direction "ρ" , transverse to dielectric interfaces "z" and "φ", for cylindrical coordinates, thus taking the general equations of electromagnetic fields in function of e [1]. It is worth mentioning that in order to obtain results, simulations and analysis of the structure under study was used HFSS program (High Frequency Structural Simulator) that uses the finite element method. With the theory developed computational resources were used to obtain the numerical calculations, using Fortran Power Station, Scilab and Wolfram Mathematica ®. The prototype was built using, as a substrate, the ULTRALAM ® 3850, of Rogers Corporation, and an aluminum plate as a cylindrical structure used to support. The agreement between the measured and simulated results validate the established processes. Conclusions and suggestions are presented for continuing this work

Otimização Topológica com Termo-elasticidade Utilizando Elementos Tri3

This work proposes a formulation for optimization of 2D-structure layouts submitted to mechanic and thermal shipments and applied an h-adaptive filter process which conduced to computational low spend and high definition structural layouts. The main goal of the formulation is to minimize the structure mass submitted to an effective state of stress of von Mises, with stability and lateral restriction variants. A criterion of global measurement was used for intents a parametric condition of stress fields. To avoid singularity problems was considerate a release on the stress restriction. On the optimization was used a material approach where the homogenized constructive equation was function of the material relative density. The intermediary density effective properties were represented for a SIMP-type artificial model. The problem was simplified by use of the method of finite elements of Galerkin using triangles with linear Lagrangian basis. On the solution of the optimization problem, was applied the augmented Lagrangian Method, that consists on minimum problem sequence solution with box-type restrictions, resolved by a 2nd orderprojection method which uses the method of the quasi-Newton without memory, during the problem process solution. This process reduces computational expends showing be more effective and solid. The results materialize more refined layouts with accurate topologic and shape of structure definitions. On the other hand formulation of mass minimization with global stress criterion provides to modeling ready structural layouts, with violation of the criterion of homogeneous distributed stress

Método de Otimização Topológica em Estruturas Tridimensionais

The topology optimization problem characterize and determine the optimum distribution of material into the domain. In other words, after the definition of the boundary conditions in a pre-established domain, the problem is how to distribute the material to solve the minimization problem. The objective of this work is to propose a competitive formulation for optimum structural topologies determination in 3D problems and able to provide high-resolution layouts. The procedure combines the Galerkin Finite Elements Method with the optimization method, looking for the best material distribution along the fixed domain of project. The layout topology optimization method is based on the material approach, proposed by Bendsoe & Kikuchi (1988), and considers a homogenized constitutive equation that depends only on the relative density of the material. The finite element used for the approach is a four nodes tetrahedron with a selective integration scheme, which interpolate not only the components of the displacement field but also the relative density field. The proposed procedure consists in the solution of a sequence of layout optimization problems applied to compliance minimization problems and mass minimization problems under local stress constraint. The microstructure used in this procedure was the SIMP (Solid Isotropic Material with Penalty). The approach reduces considerably the computational cost, showing to be efficient and robust. The results provided a well defined structural layout, with a sharpness distribution of the material and a boundary condition definition. The layout quality was proporcional to the medium size of the element and a considerable reduction of the project variables was observed due to the tetrahedrycal element

Modelagem numérica de estruturas de contenção atirantadas em areia

A numerical study on the behavior of tied-back retaining walls in sand, using the finite element method (FEM) is presented. The analyses were performed using the software Plaxis 2D, and were focused on the development of horizontal displacements, horizontal stresses, shear forces and bending moments in the structure during the construction process. Emphasis was placed on the evaluation of wall embedment, tie-back horizontal spacing, wall thickness, and free anchor length on wall behavior. A representative soil profile of a specific region at the City of Natal, Brazil, was used in the numerical analyses. New facilities built on this region often include retaining structures of the same type studied herein. Soil behavior was modeled using the Mohr-Coulomb constitutive model, whereas the structural elements were modeled using the linear elastic model. Shear strength parameters of the soil layers were obtained from direct shear test results conducted with samples collected at the studied site. Deformation parameters were obtained from empirical correlations from SPT test results carried out on the studied site. The results of the numerical analyses revealed that the effect of wall embedment on the investigated parameters is virtually negligible. Conversely, the tie-back horizontal spacing plays an important role on the investigated parameters. The results also demonstrated that the wall thickness significantly affects the wall horizontal displacements, and the shear forces and bending moments within the retaining structure. However, wall thickness was not found to influence horizontal stresses in the structure

Modelos para análise e dimensionamento de painéis de alvenaria estrutural

The main objective of this thesis was the study of bracing panels of structural masonry, by applying the Finite Element Method and Strut and Tie Method. It was analyzed the following aspects: the effect of orthotropy on the behavior of the panels; distribution of horizontal forces between panels for buildings; comparison between Equivalent Frame and Finite Elements models; panels design with the Strut and Tie Method. The results showed that one should not disregard the orthotropy, otherwise this can lead to models stiffer than the real. Regarding the distribution of horizontal forces, showed that the disregard of lintels and shear deformation leads to significant differences in the simplified model. The results showed also that the models in Finite Element and Equivalent Frame exhibit similar behavior in respect to stiffness of panels and stress distribution over the sessions requested. It was discussing criteria for designing Strut and Tie Method models in one floor panels. Then, the theoretical strength these panels was compared with the rupture strength of panels tested in the literature. The theoretical maximum strength were always less than the rupture strength of the panels obtained in tests, due to the fact that the proposed model cannot represent the behavior of the masonry after the start of the panel cracking due to plasticization of the reinforcement

Desenvolvimento de antenas de microfita e antenas DRA Broadband

The search for ever smaller device and without loss of performance has been increasingly investigated by researchers involving applied electromagnetics. Antennas using ceramics materials with a high dielectric constant, whether acting as a substract element of patch radiating or as the radiant element are in evidence in current research, that due to the numerous advantages offered, such as: low profile, ability to reduce the its dimensions when compared to other devices, high efficiency of ratiation, suitability the microwave range and/or millimeter wave, low temperature coefficient and low cost. The reason for this high efficiency is that the dielectric losses of ceramics are very low when compared to commercially materials sold used in printed circuit boards, such as fiberglass and phenolite. These characteristics make ceramic devices suitable for operation in the microwave band. Combining the design of patch antennas and/or dielectric resonator antenna (DRA) to certain materials and the method of synthesis of these powders in the manufacture of devices, it s possible choose a material with a dielectric constant appropriate for the design of an antenna with the desired size. The main aim of this work is the design of patch antennas and DRA antennas on synthesis of ceramic powders (synthesis by combustion and polymeric precursors - Pe- chini method) nanostructured with applications in the microwave band. The conventional method of mix oxides was also used to obtain nanometric powders for the preparation of tablets and dielectric resonators. The devices manufactured and studied on high dielectric constant materials make them good candidates to have their small size compared to other devices operating at the same frequency band. The structures analyzed are excited by three different techniques: i) microstrip line, ii) aperture coupling and iii) inductive coupling. The efficiency of these techniques have been investigated experimentally and compared with simulations by Ansoft HFSS, used in the accurate analysis of the electromagnetic behavior of antennas over the finite element method (FEM). In this thesis a literature study on the theory of microstrip antennas and DRA antenna is performed. The same study is performed about the materials and methods of synthesis of ceramic powders, which are used in the manufacture of tablets and dielectric cylinders that make up the devices investigated. The dielectric media which were used to support the analysis of the DRA and/or patch antennas are analyzed using accurate simulations using the finite difference time domain (FDTD) based on the relative electrical permittivity (er) and loss tangent of these means (tand). This work also presents a study on artificial neural networks, showing the network architecture used and their characteristics, as well as the training algorithms that were used in training and modeling some parameters associated with the devices investigated

Análise e síntese de antenas e superfícies seletivas de frequência utilizando computação evolucionária e inteligência de enxames

The frequency selective surfaces, or FSS (Frequency Selective Surfaces), are structures consisting of periodic arrays of conductive elements, called patches, which are usually very thin and they are printed on dielectric layers, or by openings perforated on very thin metallic surfaces, for applications in bands of microwave and millimeter waves. These structures are often used in aircraft, missiles, satellites, radomes, antennae reflector, high gain antennas and microwave ovens, for example. The use of these structures has as main objective filter frequency bands that can be broadcast or rejection, depending on the specificity of the required application. In turn, the modern communication systems such as GSM (Global System for Mobile Communications), RFID (Radio Frequency Identification), Bluetooth, Wi-Fi and WiMAX, whose services are highly demanded by society, have required the development of antennas having, as its main features, and low cost profile, and reduced dimensions and weight. In this context, the microstrip antenna is presented as an excellent choice for communications systems today, because (in addition to meeting the requirements mentioned intrinsically) planar structures are easy to manufacture and integration with other components in microwave circuits. Consequently, the analysis and synthesis of these devices mainly, due to the high possibility of shapes, size and frequency of its elements has been carried out by full-wave models, such as the finite element method, the method of moments and finite difference time domain. However, these methods require an accurate despite great computational effort. In this context, computational intelligence (CI) has been used successfully in the design and optimization of microwave planar structures, as an auxiliary tool and very appropriate, given the complexity of the geometry of the antennas and the FSS considered. The computational intelligence is inspired by natural phenomena such as learning, perception and decision, using techniques such as artificial neural networks, fuzzy logic, fractal geometry and evolutionary computation. This work makes a study of application of computational intelligence using meta-heuristics such as genetic algorithms and swarm intelligence optimization of antennas and frequency selective surfaces. Genetic algorithms are computational search methods based on the theory of natural selection proposed by Darwin and genetics used to solve complex problems, eg, problems where the search space grows with the size of the problem. The particle swarm optimization characteristics including the use of intelligence collectively being applied to optimization problems in many areas of research. The main objective of this work is the use of computational intelligence, the analysis and synthesis of antennas and FSS. We considered the structures of a microstrip planar monopole, ring type, and a cross-dipole FSS. We developed algorithms and optimization results obtained for optimized geometries of antennas and FSS considered. To validate results were designed, constructed and measured several prototypes. The measured results showed excellent agreement with the simulated. Moreover, the results obtained in this study were compared to those simulated using a commercial software has been also observed an excellent agreement. Specifically, the efficiency of techniques used were CI evidenced by simulated and measured, aiming at optimizing the bandwidth of an antenna for wideband operation or UWB (Ultra Wideband), using a genetic algorithm and optimizing the bandwidth, by specifying the length of the air gap between two frequency selective surfaces, using an optimization algorithm particle swarm

Desenvolvimento de um ressoador retangular de fenda com múltiplas camadas de substrato e com utilização de material PBG para sistema de comunicação sem fio

In the globalized world modern telecommunications have assumed key role within the company, causing a large increase in demand for the wireless technology of communication, which has been happening in recent years have greatly increased the number of applications using this technology. Due to this demand, new materials are developed to enable new control mechanisms and propagation of electromagnetic waves. The research to develop new technologies for wireless communication presents a multidisciplinary study that covers from the new geometries for passive antennas, active up to the development of materials for devices that improve the performance at the frequency range of operation. Recently, planar antennas have attracted interest due to their characteristics and advantages when compared with other types of antennas. In the area of mobile communications the need for antennas of this type has become increasingly used, due to intensive development, which needs to operate in multifrequency antennas and broadband. The microstrip antennas have narrow bandwidth due to the dielectric losses generated by irradiation. Another limitation is the degradation of the radiation pattern due to the generation of surface waves in the substrate. Some techniques have been developed to minimize this limitation of bandwidth, such as the study of type materials PBG - Photonic Band Gap, to form the dielectric material. This work has as main objective the development project of a slot resonator with multiple layers and use the type PBG substrate, which carried out the optimization from the numerical analysis and then designed the device initially proposed for the band electromagnetic spectrum between 3-9 GHz, which basically includes the band S to X. Was used as the dielectric material RT/Duroid 5870 and RT/Duroid 6010.LM where both are laminated ceramic-filled PTFE dielectric constants 2.33 and 10.2, respectively. Through an experimental investigation was conducted an analysis of the simulated versus measured by observing the behavior of the radiation characteristics from the height variation of the dielectric multilayer substrates. We also used the LTT method resonators structures rectangular slot with multiple layers of material photonic PBG in order to obtain the resonance frequency and the entire theory involving the electromagnetic parameters of the structure under consideration. xviii The analysis developed in this work was performed using the method LTT - Transverse Transmission Line, in the field of Fourier transform that uses a component propagating in the y direction (transverse to the real direction of propagation z), thus treating the general equations of the fields electric and magnetic and function. The PBG theory is applied to obtain the relative permittivity of the polarizations for the sep photonic composite substrates material. The results are obtained with the commercial software Ansoft HFSS, used for accurate analysis of the electromagnetic behavior of the planar device under study through the Finite Element Method (FEM). Numerical computational results are presented in graphical form in two and three dimensions, playing in the parameters of return loss, frequency of radiation and radiation diagram, radiation efficiency and surface current for the device under study, and have as substrates, photonic materials and had been simulated in an appropriate computational tool. With respect to the planar device design study are presented in the simulated and measured results that show good agreement with measurements made. These results are mainly in the identification of resonance modes and determining the characteristics of the designed device, such as resonant frequency, return loss and radiation pattern

Análise de antenas utilizando substrato cerâmico, zpt, produzido por síntese auto propagante para aplicações em sistemas de micro-ondas

Ceramic substrates have been investigated by researchers around the world and has achieved a high interest in the scientific community, because they had high dielectric constants and excellent performance in the structures employed. Such ceramics result in miniaturized structures with dimensions well reduced and high radiation efficiency. In this work, we have used a new ceramic material called lead zinc titanate in the form of Zn0,8Pb0,2TiO3, capable of being used as a dielectric substrate in the construction of various structures of antennas. The method used in constructing the ceramic combustion synthesis was Self- Sustained High Temperature (SHS - "Self-Propagating High-Temperature Synthesis") which is defined as a process that uses highly exothermic reactions to produce various materials. Once initiated the reaction area in the reaction mixture, the heat generated is sufficient to become self-sustaining combustion in the form of a wave that propagates converting the reaction mixture into the product of interest. Were analyzed aspects of the formation of the composite Zn0,8Pb0,2TiO3 by SHS powders and characterized. The analysis consisted of determining the parameters of the reaction for the formation of the composite, as the ignition temperature and reaction mechanisms. The production of composite Zn0,8Pb0,2TiO3 by SHS performed in the laboratory, was the result of a total control of combustion temperature and after obtaining the powder began the development of ceramics. The product was obtained in the form of regular, alternating layers of porous ceramics and was obtained by uniaxial pressing. 10 The product was characterized by analysis of dilatometry, X-ray diffraction analysis and scanning electron microscopy. One of the contributions typically defined in this work is the development of a new dielectric material, nevertheless presented previously in the literature. Therefore, the structures of the antennas presented in this work consisted of new dielectric ceramics based Zn0,8Pb0,2TiO3 usually used as dielectric substrate. The materials produced were characterized in the microwave range. These are dielectrics with high relative permittivity and low loss tangent. The Ansoft HFSS, commercial program employee, using the finite element method, and was used for analysis of antennas studied in this work

Materiais supercondutores HTS para arranjos de antenas e aplicação de PBG para micro-ondas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Síntese de superfícies seletivas de frequência atráves de técnicas de computação natural

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Estudo do efeito de substratos metamateriais em parâmetros de antenas de microfita

Microstrip antennas are subject matter in several research fields due to its numerous advantages. The discovery, at 1999, of a new class of materials called metamaterials - usually composed of metallic elements immersed in a dielectric medium, have attracted the attention of the scientific community, due to its electromagnetic properties, especially the ability to use in planar structures, such as microstrip, without interfering with their traditional geometry. The aim of this paper is to analyze the effects of one and bidimensional metamaterial substrates in microstrip antennas, with different configurations of resonance rings, SRR, in the dielectric layer. Fractal geometry is applied to these rings, in seeking to verify a multiband behavior and to reduce the resonance frequency of the antennas. The results are then given by commercial software Ansoft HFSS, used for precise analysis of the electromagnetic behavior of antennas by Finite Element Method (FEM). To reach it, this essay will first perform a literature study on fractal geometry and its generative process. This paper also presents an analysis of microstrip antennas, with emphasis on addressing different types of substrates as part of its electric and magnetic anisotropic behavior. It s performed too an approach on metamaterials and their unique properties

Viabilidade da Utilização de Máquinas de Indução Convencionais como Motores sem Mancais Mecânicos

Electrical Motors transform electrical energy into mechanic energy in a relatively easy way. In some specific applications, there is a need for electrical motors to function with noncontaminated fluids, in high speed systems, under inhospitable conditions, or yet, in local of difficult access and considerable depth. In these cases, the motors with mechanical bearings are not adequate as their wear give rise to maintenance. A possible solution for these problems stems from two different alternatives: motors with magnetic bearings, that increase the length of the machine (not convenient), and the bearingless motors that aggregate compactness. Induction motors have been used more and more in research, as they confer more robustness to bearingless motors compared to other types of machines building with others motors. The research that has already been carried out with bearingless induction motors utilized prototypes that had their structures of stator/rotor modified, that differ most of the times from the conventional induction motors. The goal of this work is to study the viability of the use of conventional induction Motors for the beringless motors applications, pointing out the types of Motors of this category that can be more useful. The study uses the Finite Elements Method (FEM). As a means of validation, a conventional induction motor with squirrel-cage rotor was successfully used for the beringless motor application of the divided winding type, confirming the proposed thesis. The controlling system was implemented in a Digital Signal Processor (DSP)