Doutorado em Engenharia Mecânica

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Agora exibindo 1 - 5 de 31

Estudo de duas técnicas para a solução de problemas dinâmicos utilizando o método dos elementos de contorno: a superposição modal e a transformada de Laplace
(Universidade Federal do Espírito Santo, 2024-12-20) Santos, Aquila de Jesus dos; Lara, Luciano de Oliveira Castro; Loeffler Neto, Carlos Friedrich; https://orcid.org/0000-0002-5754-6368; Saenz, Juan Sérgio Romero; Campos, Lucas Silveira; Bulcão, André; Albuquerque, Éder Lima de
The search for a reliable and accurate method to convert domain integrals involving non-self-adjoint operators into boundary integrals, in accordance with the philosophy of the Boundary Element Method, remains a significant challenge. One of the most recent proposals to achieve this goal is the Direct Interpolation Technique of the Boundary Element Method (DIBEM). Already successfully employed in solving scalar problems governed by the Poisson, Helmholtz, and Advection-Diffusion equations, this work presents the results of using DIBEM in the analysis of wave propagation problems in homogeneous media. The main objective is to evaluate the integration of DIBEM with two distinct techniques for handling the time-dependent term: Modal Superposition and the Laplace Transform, two well-established strategies. In the first formulation, a modified modal superposition, which uses a correlated eigenvalue problem associated with the transpose of the dynamic matrix, is applied to decouple the dynamic equations. Time advancement is performed using the Houbolt algorithm, whose fictitious damping eliminates spurious modal contents, producing greater stability. In the second formulation, the Laplace transform is used to eliminate time dependence; DIBEM is used to solve the resulting stationary problem in terms of the transformation variable, and an inversion method is used to return to the time domain. Several typical wave propagation problems were solved using linear boundary elements.
Redução de arrasto em escoamento monofásico e bifásico (líquido-líquido) com adição de polímeros solúveis em água e hidrocarbonetos
(Universidade Federal do Espírito Santo, 2025-01-10) Barbosa, Kelvin Cristien de Oliveira; Soares, Edson José ; https://orcid.org/0000-0003-4967-4957; http://lattes.cnpq.br/4485206584533650; https://orcid.org/0000-0003-0752-1485; http://lattes.cnpq.br/6938448221920237; Siqueira, Renato do Nascimento ; https://orcid.org/0000-0002-8397-8180; http://lattes.cnpq.br/9791817633014124; Ramos, Rogério; https://orcid.org/0000-0003-4493-2435; http://lattes.cnpq.br/2975022316691139; Franco, Admilson Teixeira ; https://orcid.org/0000-0002-7977-6404; http://lattes.cnpq.br/3561428456009236; Oliveira, Márcia Cristina Khalil de ; https://orcid.org/0000-0001-8820-8567; http://lattes.cnpq.br/2392018269619309
This work presents an experimental study on drag reduction (DR) in single-phase and liquid-liquid two-phase turbulent flows through the addition of polymers. The literature contains studies on drag reduction in two-phase flows; however, most investigations focus on gas-liquid flows or liquid-liquid flows with the polymer dissolved in the aqueous phase. In various industrial sectors, two-phase flow is a common occurrence, particularly in the oil and gas industry, where one of the main objectives is to enhance production flow rates. Consequently, there is growing interest in studying the effects of drag-reducing polymer additives in two-phase flows. The objective of this study is to evaluate the effect of polymers (soluble in both water and hydrocarbons) on pressure gradient reduction (drag reduction) and to analyze polymer degradation in single-phase and liquid-liquid two-phase flows. A water-soluble polymer (Diutan Gum 3 DG) and a hydrocarbon-soluble polymer (Polyisobutylene 3 PIB) with three different molecular weights are used. For the hydrocarbon-soluble polymer, rheological characterization, preliminary DR tests in single-phase flows, and degradation analysis for the three molecular weights are performed. As expected, drag reduction increases with higher polymer concentration and molecular weight. In two-phase flow experiments, the flow pattern is dispersed due to high flow rates. The effects of DG and PIB solutions are analyzed separately and in combination. It is concluded that drag-reducing additives are more effective in the dominant phase, meaning that the water-soluble additive is effective for water fractions greater than 0.5, while the hydrocarbon-soluble additive is effective for water fractions below 0.5. As expected, increasing DG concentration results in higher DR; however, an increase in flow rate when using only DG does not lead to further DR improvement. On the other hand, for PIB, an increase in flow rate results in greater DR. When both phases contain additives, a reduction in pressure is observed compared to the case without additives across the entire range of water fractions. Additionally, it is noted that at low concentrations (low water fractions), water droplets also contribute to drag reduction. PIB degradation increases as the total two-phase flow rate rises and is further intensified when the aqueous phase is also treated with additives
O método dos elementos de contorno com interpolação direta aplicado aos problemas escalares de onda em meios homogêneos
(Universidade Federal do Espírito Santo, 2024-12-16) Santos, Gyslane Aparecida Romano dos; Lara, Luciano de Oliveira Castro ; https://orcid.org/0000-0003-1329-2957; http://lattes.cnpq.br/1675675424615229; Loeffler Neto, Carlos Friedrich; https://orcid.org/0000-0002-5754-6368; http://lattes.cnpq.br/3102733972897061; https://orcid.org/0009-0008-0138-3556; http://lattes.cnpq.br/0314997680090929; Bulcão, André ; https://orcid.org/0000-0002-9871-9683; http://lattes.cnpq.br/2273897370773348; Chacaltana, Julio Tomás Aquije ; https://orcid.org/0000-0003-2488-6232; http://lattes.cnpq.br/9108224414966705; Campos, Lucas Silveira ; https://orcid.org/; http://lattes.cnpq.br/0275751616450131; Mansur, Webe João ; https://orcid.org/0000-0001-6033-9653; http://lattes.cnpq.br/9499429606822923
The search for a consistent and accurate method for transforming domain integrals composed of non-self-adjoint operators into contour integrals, strictly following the philosophy of the Boundary Element Method, is still a challenge to be overcome. The Direct Interpolation of the Contour Element Method (DIBEM) technique is among the most recent proposals to achieve this goal. After being successful in solving scalar problems governed by the Poisson, Helmholtz and Advection Diffusion equations, this work presents the results of the DIBEM procedure in approaching acoustic wave propagation problems in homogeneous media. The main objective is to achieve greater stability of the discrete model, particularly examining the numerical characteristics of the mass matrix or acoustic inertia, which is generated approximately through a sequence of radial basis functions. Some of the best-known full support radial functions were tested, several matrix conditioning standards were verified, the degrees of positivity of the matrix related to the modal content were evaluated and the minimum time steps achieved with the refinement of the mesh were investigated. contouring and insertion of interpolating internal points. The time advance scheme used was the Houbolt algorithm, whose fictitious damping eliminates spurious modal contents, related to high frequencies, producing greater stability and accuracy. Several typical wave propagation problems in bars and membranes were solved, using linear boundary elements with DIBEM to compare with the analytical solutions of displacement and stresses in several cases
Flows and systems disaggregation for thermoeconomic modeling in thermal system analysis
(Universidade Federal do Espírito Santo, 2024-11-08) Santos, Rodrigo Guedes dos; Lourenço, Atílio Barbosa ; https://orcid.org/0000-0003-3375-6237; http://lattes.cnpq.br/5684849692205161; Serra de Renobales, Luis María; https://orcid.org/0000-0002-5161-7209; http://lattes.cnpq.br/; Lozano Serrano, Miguel Ángel ; https://orcid.org/0000-0002-4411-9834; http://lattes.cnpq.br/; Santos, José Joaquim Conceição Soares ; https://orcid.org/0000-0003-3695-2014; http://lattes.cnpq.br/6666040476009642; https://orcid.org/0000-0003-3659-7737; http://lattes.cnpq.br/1710594961530586; Martins, Márcio Ferreira ; https://orcid.org/0000-0002-3023-222X; http://lattes.cnpq.br/7325983059020104; Silva, Julio Augusto Mendes da ; https://orcid.org/0000-0002-2006-8462; http://lattes.cnpq.br/3724171990188048; Palacios Bereche, Reynaldo ; https://orcid.org/0000-0002-4810-8868; http://lattes.cnpq.br/4511646102728382; Pina, Eduardo Antonio ; https://orcid.org/0000-0001-8350-6485; http://lattes.cnpq.br/2218436088598565
Thermoeconomics is an interdisciplinary field that integrates concepts from thermodynamics and economics, providing insights that extend beyond traditional energy and economic analyses. A critical aspect of thermoeconomic modeling is the determination of the productive structure. Exergy serves as an appropriate thermodynamic parameter for cost allocation, incorporating the first and second laws of thermodynamics, assessing the quality of energy flows, and identifying subsystem irreversibilities. However, specific applications require the disaggregation of exergy. As the field evolves, the study of complex thermal systems reveals a growing number of plants with diverse equipment and challenges related to the isolation of dissipative equipment, waste cost allocation, and environmental considerations. Various thermoeconomic methodologies focused on the disaggregation of physical exergy have emerged; however, none have successfully addressed the simultaneous isolation of dissipative equipment and waste cost allocation while maintaining low model complexity. Consequently, these issues remain subjects for further exploration. This study presents ideas related to the disaggregation of flows and systems as approaches to address the identified problems. The A&F Model introduces a novel methodology for disaggregating physical exergy into two components: Helmholtz energy and flow work. Furthermore, the study explores a new approach to system disaggregation, in which a thermal system is divided into smaller subsystems that, when recombined, recreate the original system. The research conducts thermodynamic and thermoeconomic analyses to present and validate the A&F Model, assessing the model's ability to manage dissipative equipment, allocate waste costs, and maintain low complexity across various thermal systems. Concurrently, the investigation of system disaggregation examines the decomposition of the steam cycle of a sugarcane cogeneration plant into subcycles, revealing significant advantages. Integrating energy billing optimization and thermoeconomic analysis in this context determines the plant's optimal operational mode while elucidating the cost formation processes of internal products, such as refinery heat, process heat, and electricity consumption. In conclusion, the ideas presented in this thesis introduce innovative approaches within thermoeconomics, primarily through disaggregation methods for flows and systems. These contributions enhance the understanding of thermal systems' cost formation processes, facilitate dissipative equipment isolation, address waste cost allocation, and maintain low modeling complexity. Furthermore, this research significantly contributes to the application of thermoeconomics in analyzing variations in market prices within cogeneration, thereby broadening the perspective on cost allocation in thermoeconomic analyses
Tribologia e Temperatura de Contato do Peek Deslizando Contra Latão, Peek e Alumina
(Universidade Federal do Espírito Santo, 2024-01-30) Camporez, Rubson Mação; Scandian, Cherlio; https://orcid.org/0000-0002-4393-719X; http://lattes.cnpq.br/8466752738430250; https://orcid.org/0000-0003-2378-025X; http://lattes.cnpq.br/2417559348617413; Mello, Valdicleide Silva e; https://orcid.org/0000-0001-6413-6650; http://lattes.cnpq.br/4147387781308845; Strey, Nathan Fantecelle; https://orcid.org/0000-0002-2568-116X; http://lattes.cnpq.br/3613706957012460; Silva, Carlos Henrique da; https://orcid.org/0000-0002-2897-4347; http://lattes.cnpq.br/6218847264452522; Souza, Roberto Martins de; https://orcid.org/0000-0002-7384-1914; http://lattes.cnpq.br/4586350967708284
The increase in contact temperature resulting from friction during sliding between bodies influences tribological behavior, leading to changes in the microstructure and properties of materials. This thermal increase can induce softening and melting of the bodies, phenomena particularly impactful in polymers due to their low glass transition and melting temperatures. Therefore, studying and predicting the contact temperature for polymeric materials is of paramount importance to maximize their tribological application. The calculation of the contact temperature can be performed by numerical methods or through mathematical models developed for problems of lesser geometric complexity and boundary conditions. Despite the relevance and presence of methodologies for determining the contact temperature, this challenge persists in contexts involving polymeric pairs. The obstacle arises from simplifications and from not considering changes in material properties as a function of temperature. A case that occurs with polymers is the alteration of thermal conductivity, which is sensitive to the molecular ordering of polymer chains, as well as to temperature and contact pressure. The literature has gaps to be filled regarding the contact temperature of polymers, especially polymer-polymer pairs. In this context, an investigation of the contact temperature of spheres and cylindrical pins (geometry) of two different diameters (dimension) of polyetheretherketone (PEEK), an ultra-high-performance polymer, sliding against brass, PEEK, and alumina discs was conducted, varying the normal load (13 different loads) and sliding velocity (0.5 and 1 m/s). Additionally, the surface temperature of the disc was measured during the test using an infrared thermal camera. Overall, it was observed that sliding velocity, geometry, dimension, and nature of the discs influenced the parameters used in calculating the contact temperature, such as heat partition and the Peclet number. In contrast, regarding the increase in flash temperature, nominal temperature, and maximum contact temperature, sliding velocity did not influence, while the geometry, dimension, and nature of the discs did. Errors between the temperature measured with the thermal camera and one of the components of the contact temperature were observed, and to improve the accuracy of the mathematical model, the use of correction factors called γ1 and γ2 was proposed, which multiply the thermal conductivities of the pin/sphere and disc, respectively. With their use, errors were reduced to zero under some conditions, increasing the applicability of the mathematical model of contact temperature.

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