Engenharia Mecânica

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http://repositorio.ufes.br/handle/10/17620

Programa de Pós-Graduação em Engenharia Mecânica

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A numerical and statistical approach to estimate state variables in flow-accelerated corrosion problems
(Universidade Federal do Espírito Santo, 2014-08-29) Moura, Bruno Furtado de; Macêdo, Marcelo Camargo Severo de; Silva, Wellington Betencurte da; Martins, Márcio Ferreira; Colaço, Marcelo José
Sequential Monte Carlo (SMC) or Particle Filter Methods became very popular in the last few years in the statistical and engineering communities. Such methods have been widely used to deal with sequential Bayesian inference problems in several fields. SMC Methods are an approximation of sequences of probability distributions of interest, using a large set of random samples, named particles there are propagated along time with a simple Sampling Importance distribution, SI, and re-sampling techniques as well. In this work we applied two Bayesian filters to a state estimation problem involving the corrosion amount-time in a contraction-expansion geometry and compared with Computational Fluid Dynamics (CFD) results. The model adopted to estimate the mass losses is based on a double resistance due to the oxygen diffusion toward the wall through the hydrodynamic boundary layer and the oxide layer. Mass loss data over time is obtained from the literature as well. The main objective of this work is to discuss and compare the performance of the following filters: Sampling Importance Re-sampling Filter (SIR Filter) and Auxiliary Sampling Importance Re-sampling Filter (ASIR Filter) in estimation of the mass losses. Also, it is discussed the influence of the corrosion products. Best results in corrosion damage estimation were obtained using the ASIR Filter.
Aferição do modelo VOF na caracterização de padrões de escoamento multifásico em tubulação horizontal e inclinada
(Universidade Federal do Espírito Santo, 2016-04-08) Lima, Marcel Pereira; Martins, Márcio Ferreira; Ramos, Rogério; Cruz, Daniel Onofre de Almeida; Cruz, Daniel Onofre de Almeida
This work aims to verify the performance of Volume of Fluid model on flow patterns characterization in horizontal and inclined circular cross section pipe. For this purpose it was used a 42 mm diameter tube with straight section of about 4.5 m in numerical and experimental tests of three flow patterns: slug, churn and stratified wavy. The fluids used were water and air in the respective flow rates of 4.99 m3/h and 9.97 m3/h for both slug and stratified wavy patterns, under15° upward and 15° downward respectively. However, churn pattern was performed under 3.49 m3/h of water and 19.95 m3/h of air in horizontal pipe.Volume of Fluid (VOF) multiphase flow model combined with k-Realizable turbulence model and scalable wall function were set inCFD commercial software, as well as specific parameters for temporal discretization and mesh refinement, besides spatial discretization methods consistent with the flows. The set of parametersand numerical methods were based on the literature and the mesh refinement was set according to mesh test. In order to evaluate the performance of the numerical modeling, images from experimental flow were compared to the numerical ones and the literature, giving good agreement between them
Análise comparativa de aços ARBL usados na fabricação de tubos flexíveis para produção de petróleo no mar, em formações com baixo teor de H2S : um estudo de FPH utilizando solução de tiossulfato de sódio
(Universidade Federal do Espírito Santo, 2006-06-02) Girelli, Rosental Alves; Scandian, Cherlio; Macêdo, Marcelo Camargo Severo de; 1º membro da banca
This document is an experimental study of the Stress Corrosion Cracking (SCC) and Hydrogen Embrittlement (HE) behavior of a Brazilian high-strength low-alloy steel, in media with low content of H2S. It is intended to begin a qualification process of the material, which is already used in flexible pipes for petroleum production operations at the sea in situations where there is no H2S presence, to also act in cases where low concentration of this gas exists. A heat treatment is proposed for the resistance improvement of the material in these environments. The base for experimental results comparison was another material, a French one, which is already qualified and used in flexible pipes for sour oil (with H2S) production. Hence, three materials were tested: the original Brazilian one, without heat treatment (it is used in flexible pipes, in situations without H2S), the same material with the heat treatment suggested for the property improvement and possible use in low H2S environments and the French one (qualified material used in flexible pipes for oil production operations, in situations where the presence of H2S is a reality). The SCC Slow Strain Rate and Constant Strain techniques were used as the experimental tests and the media was an aqueous solution of NaCl with micro addictions of sodium thiosulfate (Na2S2O3), indicated to simulate corrosive environments with low concentration of H2S. Damage parameters (energy), embrittlement measurements, tensile properties and also fracture features of the specimens were evaluated at the comparative analysis of the materials.
Análise comparativa de medidor de vazão em flare por tecnologia ótica e pitometria utilizando túnel de vento
(Universidade Federal do Espírito Santo, 2012-07-25) Silva, Felipe Carvalho da; Ramos, Rogério; Loureiro, Bruno Venturini; Mattos, Márcio Coelho de; Soares, Márcio Martins
With recent discoveries by the oil industry related to the reserves in Brazilian pre-salt, flow measurement technology is being re-evaluated in view of the large CO2 concentrations found in these reserves. A technology that has accuracy levels similar to those obtained with flow meters currently used and also measures independent characteristics to the composition and thermodynamic properties of gases is optical flow measurement velocimetry (OFM). The present work is related to experimental study, comparison of the speed readings from Pitot tube flow meters and optical velocimetry. This experimental study consists of qualifying and quantifying the velocity profiles among the possible configurations of flow in the wind tunnel, proposing methodology using flow conditioners and damping of the readings obtained with the Pitot tube, and analysis of readings taken with the optical sensor to evaluate the device installation effects in the results. The results indicate that transit-time optical flow meters for medium to high speed levels, could provide readcohesive flow even in a misalignment of up to ± 5 °, although it appears in the installation manual of the manufacturer guarantees of results meter when a misalignment of at most up to ±2º. Regarding the optical sensor intrusive effect in the readings simultaneous with the Pitot tube, it is perceived, in general, from approximately Re> 2,05x105, the intrusive effect of this influence is suppressed by other effects. Finally, for a proper flow study through Pitometry in order to make the comparison with the optical flow metering and achieve satisfactory results with the Pitot tube, the use of specific devices of flow conditioning and damping of the measured values had to be made
Análise da dinâmica acoplada de um motor de indução trifásico montado sobre uma base elástica
(Universidade Federal do Espírito Santo, 2013-10-15) Ganda, Wenderson Luiz; Mattos, Márcio Coelho de; Loeffler Neto, Carlos Friedrich; Fardin, Jussara Farias; Rocha, Roger
The dynamic analysis of systems compound by electric motor and its support structure its very important, because there is an interaction between them and the mutual influence generate various phenomena during its operation. With mathematical models is possible to simulate the dynamical behavior of these systems, with the objective of represent an actual condition and to predict the system response. These answers provide information that can be applied in solutions to the problems during project stage and assist failure analysis. In recent years, the drives based in Direct Current Motors (DCM) have been gradually substituted by drives based in Alternate Current Three-phase Induction Motor (TIM). The coupled dynamic analysis of DCM and its structure base have been widely studded and the phenomena that occur modeled. The objective of this study is to analyze the systems compound by an elastic base support and a three-phase induction motor by coupled dynamic models, to identify and verify if non-linear oscillation phenomena are relevant to this type of motor.
Análise da dinâmica acoplada de uma máquina elétrica rotativa e sua estrutura de suporte
(Universidade Federal do Espírito Santo, 2004-12-22) Rocha Junior, Edmilson Bermudes; Mattos, Márcio Coelho de; Simonetti, Domingos Sávio Lyrio; Balthazar, José Manoel
It’s performed in this work the dynamics of the analyzes of a system made of a directcurrent electrical unbalanced engine, supported by an elastic structure. This kind ofsystem is seen as an non-ideal system, that is, an interaction between the engineand the electrical system. The importance of the study of problems involving thedocking of dynamics of various systems has increased through the constructivecharacteristics of the machines and its structures. It is believed that the constructivemachines tend to be more flexible and may work in higher rotations as well. Then,some phenomena that were not noticed in other generation machines can beobserved now and the use of a more complete models are necessary to explain it.On the operational side a bigger demand of the control system is made even morenecessary. The set of equations that lead the system studied in this work engine-structure is composed by the mechanical equations resulted from the Lagrangeequations and the ones from the Kirchhoff law tension. Moreover, the Runge-Kuttafivth order is used , with a variable pitch aiming at the simulation system. Finally, theanalyzes of the electrical motor arousal independence and series performance isrealized, taking into account the influence of the structure over the rotation.
Análise da influência de tratamento térmico na resistência à corrosão-erosão do aço inoxidável AISI 304
(Universidade Federal do Espírito Santo, 2008-12-18) Louzada, Dímisson Abreu; Macêdo, Marcelo Camargo Severo de; Franco, Sinésio Domingues; Bozzi, Antônio César
This work intends to evaluate the damaged caused by the erosion-corrosion process of a stainless steels AISI 304, under four microstructures conditions, used in various applications by the erosion, corrosion, and erosion-corrosion rates. With these rates it is possible to verify if there is a synergistic effect under the test conditions. For that reason, a slurry pot tester was useful. The experiments were performed at an impact of 7,5 m/s at room temperature. The abrasive particles of quartz used are in granulometric range 150 μm and an average sand concentration of 4 % wt. The corrosion and erosion-corrosion tests were performed in a solution of sodium chloride and acetic acid with 10-3 mol/l of sodium thiosulfate which is used to simulate the effect of the H2S presence. The samples obtained from dowel steel are cylindrical with 4,76 mm diameter and were weighted before and after each test. The erosion rate is in good agreement with the literature and is higher for solubility samples. The erosion rate is higher than the corrosion rate. The synergistic effect was observed for the test conditions.
Análise da influência de tratamento térmico na resistência a corrosão-erosão do aço inoxidável AISI 304
(Universidade Federal do Espírito Santo, 2008-12-18) Louzada, Dímisson Abreu; Macêdo, Marcelo Camargo Severo de; Bozzi, António Cesar; Franco, Sinésio Domingues
This work intends to evaluate the damaged caused by the erosion-corrosion process of a stainless steels AISI 304, under four microstructures conditions, used in various applications by the erosion, corrosion, and erosion-corrosion rates. With these rates it is possible to verify if there is a synergistic effect under the test conditions. For that reason, a slurry pot tester was useful. The experiments were performed at an impact of 7,5 m/s at room temperature. The abrasive particles of quartz used are in granulometric range 150 µm and an average sand concentration of 4 % wt. The corrosion and erosion-corrosion tests were performed in a solution of sodium chloride and acetic acid with 10-3 mol/l of sodium thiosulfate which is used to simulate the effect of the H2S presence. The samples obtained from dowel steel are cylindrical with 4,76 mm diameter and were weighted before and after each test. The erosion rate is in good agreement with the literature and is higher for solubility samples. The erosion rate is higher than the corrosion rate. The synergistic effect was observed for the test conditions.
Análise da tensão limite de escoamento em emulsões A/O de petróleo parafínico
(Universidade Federal do Espírito Santo, 2017-05-26) Vargas, Gabriel Gomes; Thompson, Roney Leon; Soares, Edson José; Campos, Flavio Barboza; Pereira, Fabio de Assis Ressel
Non-Newtonian fluids formed by dispersions, such as emulsions, solutions and gels,may exhibit viscoelastic, viscoplastic and thixotropic characteristics. When a waxycrude oil is subjected to low temperatures, its paraffin crystals precipitated, giving riseto a resistant structure. The understanding of this behavior at this critical condition isessential to analyze the restart of production in oil wells and pipelines after a produc-tion shutdown. The dimensioning of equipment used in the starting of these systemsdepends fundamentally on the yield stress of the oil in production. The dependence ofthe rheological characteristics of petroleum with the history of shear and temperaturemakes rheological evaluations complex, sometimes imprecise and with low repeatabi-lity. In this work the analyzes were conducted in a commercial type rheometer (HaakeMars III), using plate-plate geometry. Evidence indicates that the initial oil preheatingtemperature is an important variable in the rheological behavior of the fluid. The resultsindicate that the initial increase in temperature causes a severe increase in yield stressup to80◦C, above this temperature there is a dramatic reversal in the yield stress in thetwo oils studied. It is also shown the variation of the yield stress with the change of thecooling rate that the oil is exposed and an analysis of the evaporation and loss of vo-latiles. In the complex study of emulsions, droplet size distribution measurements andmorphological studies were performed. Important considerations are discussed herewith respect to yield stress in low water cut emulsions and high water cut emulsions.Finally, a model is presented for checking the rheological parameters.Keywords: Yield stress, waxy crude oil, Emulsion.
Análise da valência do Mn e Re nos compostos cerâmicos Ca2MnReO6 e Ca1,9Y0,1 MnReO6
(Universidade Federal do Espírito Santo, 2014-04-15) Cavichini, Arthur Sant'Ana; Orlando, Marcos Tadeu D'Azeredo; Depianti, Janaina Bastos; Rossi, Jesualdo Luiz; Passamai Junior, José Luis
In this work the analysis of the valences of the rhenium and manganese was undertaken in cera-mic compounds Ca2MnReO6and Ca1.9Y0.1MnReO6using the model of valence bond. For thecalculations of distances got bonds were used by Rietveld refinement from diffraction patternsof X-rays were considered that both sites have mixed valence. The calculations for the valencemodel were performed using parameters taken from the literature. For the calculations of Re6+,was proposed parameter𝑅0= 1.93Å and for Re5+the parameters𝑅0= 1.90Å and𝑅0= 1.92Å. The results valence that best set were used to calculate the occupation factor of Re6+andRe5+at the site of rhenium, and Mn2+and Mn3+in site of manganese, as well as for calcula-ting the average valence at each site. These results were compared with the results obtained byanalyzing the valence of X-ray absorption on Mn K edge and Re L3edge. After comparison, itwas concluded that the valences of Mn and Re presents in ceramic Ca2MnReO6are+2.3±0.3and+5.6±0.3with occupation factors of68%of Mn2+ions, and32%of Mn3+ions, and61%of Re6+ion and39%of Re5+ions. The results for compound Ca1.9Y0.1MnReO6to the valencesof the rhenium were few contradictory, which led us to review the results obtained by X-ray ab-sorption. Upon review, we conclude that the valence that best fits the compound is+2.2±0.3for Mn and+5.2±0.3for Re, shown a occupancy of80%of Mn2+and20%of Mn3+on thesite of manganese, and occupancy of25%to Re6+and75%to Re5+to the rhenium site
Análise da variabilidade induzida pela concentração de co2 nas leituras de medidores de vazão ultrassônicos para gás de queima
(Universidade Federal do Espírito Santo, 2016-04-29) Barros, Weverton Ferreira; Ramos, Rogério; Guidolini , Icaro Pianca; Rezende, Luiz Augusto; Martins, Marcio Ferreira
The produced effect by the attenuating character of the carbon dioxide on the ultrasonic flowmeter performance in gas flare application was verified. For this, experiments were conducted in wind tunnel with Reynolds number at 104. The results indicates that the ultrasonic meter presented measurement failures in stages of abrupt variation of this gas and whose concentration was show higher of 5%, also being verified that an approximation of the transducers tend to reduce this failures of measurement
Análise de difusividade térmica em aço duplex UNS S32304 submetido a diferentes processos de soldagem TIG e tratamento térmico
(Universidade Federal do Espírito Santo, 2016-05-13) Bolsanello, Marilia Fernandes; Passos, Carlos Augusto Cardoso; Orlando, Marcos Tadeu D'Azeredo; Macêdo, Marcelo Camargo Severo de; Rossi, Jesualdo Luiz; Passamai Junior, José Luis
Thermal diffusivity of UNS S32304 stainless steel was evaluated with the purpose ofaggregate knowledge to the development of the radioactive material transportation containment receptacles project.The Flash Lased Method was used, which is based on unidimensional thermal diffusivity equation analytical solution. A carbon dioxide laser with Gaussian profile was used, with 10−6𝑚wavelength, 10√2𝑊𝑚2⁄intensity and 10√2𝑊𝑚2⁄diameter.A sample of material was analyzed as received, in order toobtain a reference diffusivity value, and to compare with the value provided by the supplier, which ensured the method effectiveness. Thereafter, a sample welded by TIG autogenous process, with argon shield gas, was tested to analyze the welding process influence under thermal diffusivity. A sample welded by the same procedure, but heat treated under 600 °C for 8 hours and cooled by air was also analyzed, to evaluate the effect of these steels exposure to high temperatures after welding. To do so, in both welded samples, points with variable distance to sample middle were taken, including molted zone, heat affected zone and base metal. Finally, obtained results were compared to previous optical microscopy, ray X diffraction characterization, micro hardness and residual stresses analysis. It could be observed that thermal diffusivity was affected not only by welding process but also by heat treatment. Most of the points presented reduced thermal diffusivity, assigned to a material thermal conductive reduction, harmful for the use in question, once it will respond slowly to thermal changes. The heat treated sample presented diffusivity values closer to the material as received, qualitative similar results were also observed on residual stresses tests, where thermal treatment equalized materials stress state. Besides that, the molting zone point, at the sample only welded, presented a thermal diffusivity value above the one founded at base metal, which can be related to structural changes caused by heating. Nevertheless, those are partial conclusions, reinforcing the need of deeper studies concerning stainless steel UNS S32304 thermal diffusivity.
Análise de difusividade térmica na junção metal/cerâmica UNS 32304/sílico-aluminosa 45-50
(Universidade Federal do Espírito Santo, 2018-05-07) Caliari, Hendricky Fassarella; Orlando, Marcos Tadeu D'Azeredo; Soares, Jacyra Ramos; Martins, Charles de Abreu; Passos, Carlos Augusto Cardoso
Fireclay bricks are widely used in industries where exist high temperature gradient from the working face to the cold face of the material. In the steel industry, for example, they are assembled in: blast furnaces runners, torpedo car, pig iron ladle, steel ladle, LD converter, etc.As ceramics, these materials are generally hard and brittle, have low tensile strength and impact resistance. This imposes limitations for applications when they are under mechanical stresses. In this way, an alternative is to combine the properties of the ceramic with the properties of the metals. With this objective in mind, in this dissertation, the joint of fireclay brick 45-50 in duplex stainless steel UNS 32304 was investigated. The thermal diffusivity measurements were performed with a carbon dioxide laser with Gaussian space profile, wavelength 10μ𝑚, intensity 10√2𝑊/𝑚2 and diameter equal to 2𝑚𝑚.Using UNS 32304 steel plates, several substrates with dimensions of 70x7x1,807𝑚𝑚were manufactured. Subsequently, these substrates were milled, producing rectangular channels with 2𝑚𝑚wide by 1𝑚𝑚deep. Silica-aluminous ceramics were cut with 70x2x3𝑚𝑚and coupled in these generated channels. Thermal diffusivity was measured with the flash laser method. The measurement results about thermal diffusivity in the metal / ceramic junction were close to those theoretically estimated, considering the hypothesis of additivity without interference between the compounds
Análise de falha e gerenciamento de riscos associados aos dutos de gás natural à alta pressão
(Universidade Federal do Espírito Santo, 2011-12-15) Almeida, Jerfson Pereira de; Sisquini, Geraldo Rossoni; Scandian, Cherlio; Ramos, Rogério; Freitas, Marcílio Sousa da Rocha
The failure of a natural gas pipeline could bring harm to many people and properties near the site of the same. The area of risk associated with the damage will depend on the failure mode of the pipe, ignition timing, environmental conditions at the point of failure and weather conditions. Some failures are independent of time such as third-party interference, earthquakes, over-pressure, etc. Other failures are time dependent, such as corrosion and fatigue failure. The management of gas transportation through pipelines shows that the failure rate varies significantly with the design factors, conditions of construction, maintenance techniques and environmental situations. The quantitative risk assessment has become important for controlling the level of actual danger of the pipeline. This paper proposes an approach to mechanical failures in pipes, as well as their analysis when dealing with fatigue and corrosion. Results are presented for reference beam to the area where the risk of death is imminent, a simple method of quantitative evaluation of it shows through the engineering data such as operating pressure, pipe geometry, diameter of the hole through which the gas escapes and population density of Geographic Information Systems, the results of risk for radius, length fatal and fatal accumulated length that serve as the basic parameters for decisions regarding the management of the factors associated with the disaster. The methodology presented turns out to be a good choice to be applied in managing risks associated with the transport of gas through pipelines.
Análise de incertezas da vazão volumétrica de gás natural relatada nas condições de referência
(Universidade Federal do Espírito Santo, 2017-06-07) Mosckem, Marina Duarte; Mattos, Márcio Coelho de; Ramos, Rogério; Castro, Eustáquio Vinícius R.de; Fernandes, Pedro Rafael Bolognese
It’scommonforregulationstorequirenaturalgasflowmeasurement to be reported on a volumetricbasis. Therefore, the measurement should also be reported at a specific pressure and temperature,referred toas standard conditions. In Brazil, petroleum and gasmeasurements must comply with ANP/Inmetro Ordinance 01/2013, which states the followingstandardconditions: 1 bar, 20°C. When the flowing conditions are not the same as the standard ones, the measurement must be corrected for the standard condition bymeans of thermodynamic Equations of State –EOS. Thus, themeasurement reportedin the standard conditions carries a portion of uncertainty relative to this operation, whose value depends onthe temperature and pressure, as well as on the chosen EOS. The main goal of the work is to evaluate this parcel of the uncertainty, especially incritical flowing conditions. Some typical natural gas compositionswere selected and the following flowing conditions: 50 bar, 4°C.Results obtained by means of Monte Carlo simulationshow that the measurement reported at the standard conditions carries a portion of uncertainty generally greater than1,0percentagepoints,only due to thenecessary correction just commented. It’s a significantly high value, especially if we take into account that Brazilian regulation states a maximum of 2% for fiscal measurements, for example
Análise de movimentos periódicos em sistemas bi-linear com folga simétrica
(Universidade Federal do Espírito Santo, 2012-03-27) Pancieri, José Guilherme Pelição; Mattos, Márcio Coelho de; Balthazar, José Manoel; Rangel, Angelo Gil Pezzino
This work presents the mathematical modeling of a vibrational system with the harmonically excited base. The system has been investigated by several researchers exploring many aspects of the global dynamics. However, in most of the systems studied, the systems were modeled for a vibro-impact feature. In this system, the impacts are replaced by another visco-elastic set and the moment of transition is considered as a condition of periodicity. Periodicity conditions are applied on the state at the moment of transition in order to obtain a map of the next transition based on the state of the previous one. This nonlinear map is used to obtain the conditions of existence of periodic motions with specific patterns. Applying the existence conditions, the stability of the motion can be achieved by analyzing the eigenvalues of the linearized map while taking these conditions into account
Análise de movimentos periódicos em sistemas com vibro-impacto harmonicamente excitados
(Universidade Federal do Espírito Santo, 2009-10-16) Barbosa, Danilo de Almeida; Dynnikov, Vladimir Ivanovitch; Mattos, Márcio Coelho de; Cunha, Fransergio Leite da
As mechanical systems become more flexible new phenomena of dynamic systems, before less important because of the low probability of its occurrence, gain importance. Among these are systems with vibro-impacts. Is that the Systems more flexible end up amplifying the phenomena that occur during the impacts and there is contribution these phenomena in the dynamics of the global system. This paper presents a study on systems with vibro-impact, taking as an object of particular study a mass-spring-damper excited by the base, whose movement is laterally limited by obstacles against which the moving mass collides. The system is analyzed in its dimensionless form where our research focuses on studying the conditions of existence and stability of certain types of movement. The exhaustive search of the existence and of the stability of many standard of movement is not the objective this your work. We will only describe in detail the technical and computational tools that can facilitate work like is. After this step, we present some analysis to the movement patterns most common, with interesting conclusions.
Análise dinâmica com recuperação de tensões para materiais com gradação funcional: simulação numérica e validação experimental
(Universidade Federal do Espírito Santo, 2007-10-18) Fraga Filho, Carlos Alberto Dutra; Romero, Rivânia Hermógenes Paulino de; Menandro, Fernando César Meira; Sisquini, Geraldo Rossoni; Nunes, Luiz Carlos da Silva
The objective of this work was to design and the manufacture samples of materials withbehaviors, under mechanical loads, similar to functionally graded materials (with continuousvariation of the structural properties); to perform dynamic mechanical experiments, with theproduced samples; and to obtain results of simulation for dynamic loads, in order to validatea numerical model proposed by researchers of this university for the characterization of thefunctionally graded materials.The study it was divided in the following phases: confection of the specimens, adoptionof the composed beam model for the produced specimens, preparation and realization ofdynamic mechanical experiments, obtention of analytical results for the vibration problem,definition of the numerical model applied to the problem and numerical simulation ofmechanical loads.The experimental, analytical and numerical results show similar behavior for all testedspecimens. The natural vibration frequency, despite the method of obtention (experimentalmeasurement, analytical development, numerical simulation), difers at most by 15,4313%.The proposed numerical technique is found, thus, to be adequate to the modeling of layeredmaterials
Análise dinâmica de problemas escalares não-homogêneos através do método dos elementos de contorno
(Universidade Federal do Espírito Santo, 2006-03-30) Santolin, Wagner Dalvi; Markcilei Lima, Dan; Loeffler Neto, Carlos Friedrich; Mansur, Webe João; Barra, Luiz Paulo da Silva
One of the biggest limitations of the Boundary Element Method (BEM) consists in modeling non-homogeneous problems. To minimize the onerous task to make models using the subregions technique, the Quasi-Dual Reciprocity formulation was adapted to simulate these cases. Such formulation is able to deal with heterogeneities by a special way ceding to lead the integral formulation of the mathematical model and its consequent discretization exclusively in terms of boundary values, without necessity of sub-regions. One of the most promising applications of the non-homogeneous models in the present time is the seismic analysis for prospection of oil. In these cases if it also makes necessary to represent the wave propagation phenomena, cases these, very cumbersome and complex. It is very common the numerical simulation of dynamic problems implies in badly accuracy to represent high vibration modes. This fact can distort the numerical reply sufficiently and the use of an incremental time step scheme with fictitious damping is usually requested, to avoid the tax of waste of the numerical response. Thus, this work has the objective to analyze the performance of the formularization cited in non-homogeneous problems, in which admits dynamic processes. While the Quasi-Dual formulation is used to model the material properties, the traditional Dual Reciprocity technique also is here employed, with the purpose of modeling the dynamic action.
Análise do comportamento em erosão-cavitação da liga Co-30Cr-19fe nitretada a plasma
(Universidade Federal do Espírito Santo, 2019-03-18) Oliveira, Daniela Bahiense de; Bozzi, Antônio César; Luz, Temistocles de Sousa; Silva, Flavio José da
When subjected to fluid action, operating equipment are subject to wear by cavitation erosion. To mitigate the effects of this wear, it can be used superalloys and thermochemical treatments, such as plasma nitriding. Therefore, it is necessary to promote the increase of resistance to wear by cavitational erosion of the materials used in these applications. The objective of this work was to evaluate the resistance to cavitation erosion of the plasma nitrided Co-30Cr-19Fe alloy at temperatures of 380°C, 400°C and 420°C and to determine the main wear mechanisms in each of these conditions. The samples were subjected to a solution treatment, carried out at 1200 °C for 12 hours and subsequent quenching in water. Subsequently, the thermochemical treatment of nitriding was carried out at temperatures of 380°C, 400°C and 420°C. The gas mixture used was 75% N2 and 25% H2, the treatment time was 20 hours and the working pressure was 2.5 Torr for all nitriding conditions. The characterization, before and after each treatment, was done by means of optical microscopy, microhardness measurements and X-ray diffraction. The vibration cavitation tests were performed on the ultrasonic equipment (Telsonic DG-2000) with periodically interruptions and the evolution of the mass loss and to record the evolution of the wear mechanism by scanning electron microscopy. Before the thermochemical treatment a mixed microstructure was observed whose phases are cobalt α (CFC) and ε (HC), with few carbides and precipitates. And after the solution treatment there were partial dissolution of these few carbides and precipitates that existed. S phase and chromium nitrides were obtained under all nitrided conditions. The condition that presented the greatest wear resistance due to cavitational erosion was the condition nitrided in 380°C from the analysis of the accumulated mass loss curves with the time of exposure and the evaluation of the wear mechanisms. However, the thermochemical treatment was not effective to improve the wear resistance by cavitation erosion of the nitrided conditions at 400°C and 420°C in relation to the solution treated condition. In general, the wear mechanism observed for all nitrided conditions was the absence of significant plastic deformation, with pites and craters formation, brittle detachment of the material due to fatigue and consequently absence of incubation time

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