DECIV - Artigos publicados em periódicos

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Abrasive effects of sediments on impellers of pumps used for catching raw water.
(2018) Serrano, Rodrigo Otávio Peréa; Castro, Ana Leticia Pilz de; Mancilla Rico, Edwin Andres; Pinto, Maria Aparecida; Viana, Edna Maria de Faria; Martinez, Carlos Barreira
This study presents an analysis of the abrasive effects of sediments from the bed of the Acre River, Brazil, on the wear of three different ferrous materials employed in the manufacture of impellers of centrifuge pumps used to catch raw water. In order to evaluate the abrasive wear and specific wear coefficient (k) as a function of sediment concentration, tests were conducted in samples of SAE 8620 steel, nodular cast iron and gray cast iron by using a rotary-ball abrasion meter. These tests employed abrasive slurry with concentration of 1, 2, 3, 5 and 10 g L-1 of sediments in distilled water. The volume of worn material as a function of the relative velocity of water flow in relation to the impeller blades was mathematically estimated. The experimental results showed that: i) The semi-angular and semi-rounded shapes of the sediments from the Acre River produced evidence of micro-grooving and plastic deformation in the three metallic alloys; ii) SAE 8620 steel showed higher resistance to abrasive wear than samples of gray and nodular cast iron; iii) the increase in the volume of worn material due to increment in sediment concentration and the relative velocity of the mixture (water + sediment) to the rotor pads.
Accessibility and urban mobility by bus in Belo Horizonte/Minas Gerais – Brazil.
(2019) Lessa, Daniela Antunes; Lobo, Carlos; Cardoso, Leandro
Accessibility and mobility are fundamental conditions of urban life today, which reinforces the need to evaluate the dynamics of access to and use of the public transport system in large cities that have experienced serious traffic and congestion problems. The present article analyses the levels of accessibility by bus in the city of Belo Horizonte / MG, including its relationship with the levels of urban mobility. To this end, accessibility indicators for bus and the mobility of the population are proposed. In addition, indicators of global and local regression models were evaluated, considering accessibility as an explanatory variable. In general, the results indicate a strong regional variation in the municipality of Belo Horizonte and suggest that accessibility to public transport by bus does not directly lead to effective mobility. Some regions have a greater discrepancy between the levels of accessibility and mobility, especially those located in peripheral areas where access to the bus transport system is lower than expected by the methodology, given the existing levels of mobility. The results, albeit essentially exploratory, may be useful to support the formulation of constructive measures, in order to minimize possible distortions in the provision of accessibility, encouraging the best use of mobility opportunities in urban space.
Acessibilidade ao sistema de transporte coletivo por ônibus : indicadores para os municípios da periferia metropolitana e os campos de Belo Horizonte, Brasil.
(2020) Lobo, Carlos; Cardoso, Leandro; Lessa, Daniela Antunes; Miranda, Giovanni Candido
Atualmente, o ônibus apresenta-se como primordial modo de transporte das principais metrópoles brasileiras. Com o objetivo de avaliar a acessibilidade por ônibus na Região Metropolitana de Belo Horizonte, este trabalho apresenta indicadores de acessibilidade que utilizam o número de linhas, a frequência de viagens e o total de conexões aos municípios periféricos e aos campos de Belo Horizonte (unidades espaciais da pesquisa origem- destino). Os resultados revelam alta variação regional, com maiores níveis de acessibilidade para municípios de maior porte efetivamente conurbados com a capital, como Betim e Contagem. Em Belo Horizonte, prevalecem valores mais baixos, exceto para os campos do Central Business District (cbd) e para aqueles no eixo oeste (sentido área industrial). Ao demonstrarem a elevada desigualdade regional de acessibilidade, os indicadores expostos reforçam a necessidade de investimentos para obter mais eficiência e equidade do sistema.
Acoustical and thermal performance of multilayer closing panels used in steel-structured buildings.
(2017) Ribas, Rovadávia Aline de Jesus; Souza, Henor Artur de; https://doi.org/10.1590/0370-44672014700060
This article provides an evaluation of the acoustical and thermal performance of some closing systems by referencing materials such as cement plates, plasterboard walls, precast concrete panels and expanded polystyrene. Reverberation time is calculated by applying an empirical formula, which uses temperature and relative air humidity values obtained from simulations that were conducted using the computational simulation program ESP-r (Energy Simulation Program-research). The internal temperature presented by the ESP-r is an indicator of thermal performance. Using a simplified graphic method, the acoustical performance is also evaluated by estimating the loss of sound transmission that occurs through the closing panels. Combinations of these panels, which form multilayer panels mediated by a layer of air and with or without insulating material between them, are applied. The results show that multilayered closing systems, when filled with insulating material, are an efficient solution than can provide adequate acoustical and thermal performance.
Acoustical vibration characterics of prefabricated panels employed in industrialized construction.
(2007) Souza, Henor Artur de; Neves, Francisco de Assis das; Pereira, Cristiano Cária Guimarães; Sales, Urânia Costa
With the development of industrialized steel construction, new constructive elements have been brought not only to the market, but to the everyday construction site as well and, in this way professionals and users have questioned their efficiency. In respect to vibrations in floors, what can be detected is that floor structures are thinner and a decrease of the mass in the horizontal closing panels and the utilization of new materials and systems have led them to have lower natural frequencies, and so are nearer to the frequencies produced by walking. This decrease of mass of the closing panels also lead to a considerable weakness in terms of acoustical insulation, which can cause unfavorable conditions and discomfort. Thus, it becomes necessary to do detailed studies of the efficiency of the vibration and acoustical performance of the new systems to obtain the characterization and the qualification parameters in order to optimize their use. This study does a comparative evaluation of some kinds of horizontal and vertical closing systems in respect to the vibrational and acoustical insulation performance.
Advanced inelastic analysis of steel structures at elevated temperatures by SCM/RPHM coupling.
(2018) Barros, Rafael Cesário; Maximiano, Dalilah Pires; Silveira, Ricardo Azoubel da Mota; Lemes, Igor José Mendes; Rocha, Paulo Anderson Santana
When exposed to high temperatures, the structural members and frames have their bearing capacity compromised because the physical characteristics and material resistance used in the structures deteriorate during exposure to fire, resulting in a considerable loss of strength and stiffness. In this context, the present work carries out a whole thermomechanical analysis of steel members and frames using the Finite Element Method (FEM) inelastic formulation based on the Refined Plastic Hinge Method (RPHM) coupled with the Strain Compatibility Method (SCM). The use of SCM allows for a more realistic analysis against the design codes prescriptions. So even under high temperatures, SCM is used for both evaluation of bearing capacity and stiffness parameters. To do this, the steel behavior used in the structure numerical modeling must be described in a consistent manner through its constitutive relationship. A comparison of the results obtained here with the numerical and experimental results available in the literature suggest the effectiveness of coupling SCM/RPHM and that such a methodology can provide reliable analyses of steel members and frames subjected to high temperatures.
Advanced numerical study of composite steel-concrete structures at high temperature.
(2021) Barros, Rafael Cesário; Silveira, Ricardo Azoubel da Mota; Maximiano, Dalilah Pires; Lemes, Igor José Mendes
The composite steel-concrete structures use has several advantages, such as the reduction of cross-sectional dimensions and weight of the structure, which is one of the main reasons for it is use today. However, under fire situation, the material and mechanical properties changes, causing significant strength and stiffness loss as a result of temperature rise. In this work, the temperature influence on the behavior of composite steel-concrete structures is studied through an inelastic second order (ISO) numerical investigation. For this, two computational modules, CS-ASA/FA and CS-ASA/FSA are developed and adapted for the study of composite structures in fire. The first module calculates the temperature field in any cross-section. The second module performs the ISO analysis through the coupling between the Refined Plastic Hinge Method (RPHM) and the Strain Compatibility Method (MCD). In this way, the evolution of the temperature in cross-sec- tions, the interaction diagrams between axial force and bending moment and the structures equi- librium path as a function of the time in fire are presented for composite steel-concrete beams, columns and frames. The proposed numerical methodology success is proved by comparison with experimental and numerical responses available in the literature.
Aferição de parâmetros de labirinto hidráulico em turbinas Francis: proposta de uma bancada de teste.
(2020) Castro, Ana Leticia Pilz de; Serrano, Rodrigo Otávio Peréa; Sampaio, Mila Correa; Coelho, Stenio Augusto; Pinto, Maria Aparecida; Mancilla Rico, Edwin Andres; Viana, Edna Maria de Faria; Martinez, Carlos Barreira
A geração de energia elétrica no Brasil é fortemente dependente da hidroeletricidade. As turbinas hidráulicas são máquinas responsáveis em transformar a maior parte da energia do escoamento contínuo da água que a atravessa a usina hidrelétrica em trabalho mecânico. Os principais componentes das turbinas do tipo Francis são: o rotor, o distribuidor e a caixa espiral, e é no rotor onde estão localizados os anéis de desgaste superior e inferior, e entre os anéis de desgaste os labirintos inferior e superior. Contudo, a fuga de fluido que ocorre nos labirintos das turbinas hidráulicas um dos responsáveis pelas perdas de geração de energia elétrica, vislumbrou-se a necessidade de se desenvolver um aparato que permita simular um labirinto de uma turbina Francis, afim de obter parâmetros que poderão auxiliar na tomada de decisões de projetos nesse segmento.
Air pollution perception in ten countries during the COVID-19 pandemic.
(2022) Lou, Baowen; Barbieri, Diego Maria; Passavanti, Marco; Hui, Cang; Gupta, Akshay; Hoff, Inge; Lessa, Daniela Antunes; Sikka, Gaurav; Chang, Kevin; Fang, Kevin; Lam, Louisa; Maharaj, Brij; Ghasemi, Navid; Qiao, Yaning; Adomako, Solomon; Mirhosseini, Ali Foroutan; Naik, Bhaven; Banerjee, Arunabha; Wang, Fusong; Tucker, Andrew; Liu, Zhuangzhuang; Wijayaratna, Kasun; Naseri, Sahra; Yu, Lei; Chen, Hao; Shu, Benan; Goswami, Shubham; Peprah, Prince; Hessami, Amir; Abbas, Montasir; Agarwal, Nithin
As largely documented in the literature, the stark restrictions enforced worldwide in 2020 to curb the COVID-19 pandemic also curtailed the production of air pollutants to some extent. This study investigates the perception of the air pollution as assessed by individuals located in ten countries: Australia, Brazil, China, Ghana, India, Iran, Italy, Norway, South Africa and the USA. The perceptions towards air quality were evaluated by employing an online survey administered in May 2020. Participants (N = 9394) in the ten countries expressed their opinions according to a Likert-scale response. A reduction in pollutant concentration was clearly perceived, albeit to a different extent, by all populations. The survey participants located in India and Italy perceived the largest drop in the air pollution concentration; conversely, the smallest variation was perceived among Chinese and Norwegian respondents. Among all the demographic indicators considered, only gender proved to be statistically significant.
Algae/bacteria consortium in high rate ponds : influence of solar radiation on the phytoplankton community.
(2015) Assemany, Paula Peixoto; Calijuri, Maria Lúcia; Couto, Eduardo de Aguiar do; Souza, Mauro Henrique Batalha de; Silva, Nirlane Cristiane; Santiago, Aníbal da Fonseca; Castro, Jackeline de Siqueira
Using multivariate statistical tools, the composition of the phytoplankton community was related to the characteristics of the domestic sewage used as culture medium in three high rate ponds (HRPs) submitted to different solar radiation levels. A total of 32 genera of phytoplankton were identified in the ponds; the class Chlorophyceae was the most abundant during the entire sampling period, with a larger number of individuals of the genus Desmodesmus in the summer and fall, and of the genus Chlorella in the winter and spring. The lowest occurrence of phytoplankton was observed in the fall, with behavior similar to the evolution of solar radiation throughout the year. Blocking over 30% of the solar radiation allowed for less variability of the phytoplankton community and favored the growth of biomass with higher density of individuals, as well as higher concentrations of chlorophyll-a and dissolved oxygen. On the other hand, the pond with 80% of shading presented the lowest mean density of organisms; from the perspective ofwastewater treatment, however, it can be considered the most efficient in terms of organic matter and nutrient removal. According to the regression analysis, the algal biomass in HRPs can be maximized mostly if we consider the positive effect of carbon and phosphorus and the limiting effect of nitrogen and non-biodegradable organic load. For the conditions evaluated in this study, the photoinhibition phenomenon was not observed. Other aspects such as competition with other microorganisms for space and nutrients, or predation by zooplankton, seemed to be more significant for the growth and development of algal biomass.
Alkali-activated materials produced using high-calcium, high-carbon biomass ash.
(2022) Silva, Thiago Henrique; Lara, Luis Felipe dos Santos; Silva, Guilherme Jorge Brigolini; Provis, John Lloyd; Bezerra, Augusto Cesar da Silva
Eucalyptus ash (EA) was used in this study as a high calcium ash (HCA) precursor for alkali-activated binders. The EA used also has high carbon unburned (High loss on ignition). This type of ash is one of the waste products from biomass-fuelled thermoelectric plants, and annually thousands of tons are discarded as a by-product of the energy generation process in Brasil, but it is rich in unburnt carbon which means that it is challenging to use in cementitious systems. Eucalyptus is a biomass that removes CO2 from the atmosphere by photosynthesis and part of this carbon content remains in the ashes, generating CO2 capture when EA is incorporated in the production of alkali-activated binders. The objective of the present study was to evaluate the properties of the material obtained by the alkali-activation of the high-calcium high-carbon biomass ash to generate a cementitious binder, with different pastes proportions of EA and silica fume (SF), activated by sodium hydroxide. With the different pastes, mortars were produced using standardized sand. The results obtained from the pastes and mortars were satisfactory in several aspects. The mechanical results of the alkali-activated mortars were comparable those of Portland cement mortars. Mortars degraded methylene blue more efficiently in illuminated conditions, even after high adsorption for 24 h in the dark. The content of leached ions in the remaining solutions met potability standards.
An efficient BE iterative-solver-based substructuring algorithm for 3D time-harmonic problems in elastodynamics.
(2001) Araújo, Francisco Célio de; Martins, Cláudio José; Mansur, Webe João
This work is concerned with the development of an efficient and general algorithm to solve frequency-domain problems modelled by the boundary element method based on a sub-region technique. A specific feature of the algorithm discussed here is that the global sparse matrix of the coupled system is implicitly considered, i.e. problem quantities are not condensed into interface variables. The proposed algorithm requires that only the block matrices with non-zero complex-valued coefficients be stored and manipulated during the analysis process. In addition, the efficiency of the technique presented is improved by using iterative solvers. The good performance of pre-conditioned iterative solvers for systems of equations having real-valued coefficients, well demonstrated in the literature, is confirmed for the present case where the system matrix coefficients are complex. The efficiency of the algorithm described here is verified by analysing a soil–machine foundation interaction problem. CPU time and accuracy are the parameters used for estimating the computational efficiency.
An efficient inelastic approach using SCM/RPHM coupling to study reinforced concrete beams, columns and frames under fire conditions.
(2020) Pires, Dalilah; Barros, Rafael Cesário; Silveira, Ricardo Azoubel da Mota; Lemes, Igor José Mendes; Rocha, Paulo Anderson Santana
This work has as its main objective the study of the behavior of reinforced concrete beams, columns and structural frames in a fire situation. To do so an efficient numerical formulation was developed, implemented and evaluated. When exposed to high temperatures, the characteristics of the materials deteriorate, resulting in a considerable loss of strength and stiffness of the structure. The CS-ASA (Computational System for Advanced Structural Analysis) was used to achieve the objective. This computer system was expanded for advanced analysis of structures in fire conditions, taking advantage of the existing features and adding new ones. Two new computational modules were created: CS-ASA/FA (Fire Analysis) and CS-ASA/FSA (Structural Fire Analysis). The first one was used to determine the temperature field in the structural elements’ cross-section through thermal analysis by the Finite Element Method (FEM) in permanent and transient regimes. The second was created to perform the second-order inelastic analysis of structures under fire using the FEM formulations based on the Refined Plastic Hinge Method (RPHM) and the Strain Compatibility Method (SCM) coupling, which can be considered a unique feature of the present study. The use of SCM allows for a more realistic analysis against the design codes prescriptions. Consequently, even under high temperatures, SCM is used for evaluation of both bearing capacity and stiffness parameters. The results of the nonlinear analysis in a fire situation for eight structural elements and systems with different geometries, boundary, heating and loading conditions are in good agreement with the numerical and experimental results found in the literature.
An efficient strategy for solving structural nonlinear equations by combining the orthogonal residual method and normal flow technique.
(2019) Maximiano, Dalilah Pires; Silveira, Ricardo Azoubel da Mota; Silva, Andréa Regina Dias da; Gonçalves, Paulo Batista
This paper presents a new procedure for solving structural nonlinear problems by combining the orthogonal residual method (ORM) and normal flow technique (NFT). The perpendicularity condition to the Davidenko flow, introduced by the NFT, which must be satisfied during the iterative process, overcome the difficulties, i.e. the poor convergence and inefficiency of the ORM close to the limit points, particularly the displacement limit points (snap-back behavior). Basically, the idea of the proposed strategy is to adjust the load parameter, which is treated as a variable in the nonlinear incremental-iterative solution process, assuming that the unbalanced forces (residual forces) must be orthogonal to the incremental displacements. This constraint is used together with the NFT perpendicularity condition. The proposed procedure is tested, and its efficiency is corroborated through the analyses of slender shallow and nonshallow arches and an L-frame since they exhibit highly nonlinear behaviors under certain loading conditions. It is concluded that the proposed procedure can overcome the numerical instability problems in the neighborhood of critical points when using only the conventional OR process, and the procedure compares favorably with the arc-length method, minimum residual displacement method, and generalized displacement control method.
An explicit direct FEM–BEM coupling procedure for nonlinear dynamics.
(2019) Soares Júnior, Delfim; Araújo, Francisco Célio de
In this work, an explicit direct FEM–BEM coupling procedure is proposed for nonlinear dynamics. In this procedure, each subdomain of the model is analysed separately taking into account proper interface conditions, allowing optimized solver procedures to be applied within each subdomain. In addition, the solution procedure is carried out directly (i.e., without any iterative process), since an explicit time-marching technique is employed within the FEM subdomains. In this context, a locally stabilized central difference approach is utilized, ensuring stability for the FEM analyses, as well as enhanced accuracy. Thus, a very efficient and versatile coupled solution takes place, allowing the direct and independent solution of the subdomains of the model, without regarding critical time-steps limitations within the explicit subdomains. A multi-level time-step algorithm is also considered here, enabling different time-steps to be applied to each subdomain of the model, further improving the flexibility of the coupled analyses. At the end of the paper, numerical applications are presented, illustrating the effectiveness and versatility of the proposed methodology.
An interface element for numerical analysis of flat plate/shell elements with deformable connection.
(2018) Silva, Amilton Rodrigues da; Dias, Luís Eduardo Silveira
he use of numerical methods such as the finite elements method for solving structural analysis problems is becoming ever more efficient. An interface element capable of associating flat plate/shell element in three different combinations has been developed. In a structural analysis, when only the flat plate/shell’s finite elements are used in the discretization, some problems concerning dimensional variation of the transversal section, as well as overlapping of areas can occur. . The aforementioned problems can be solved by the developed interface elements that can also simulate a possible deformable connection that is existent in the association of materials with different characteristics, such as the composite steel-concrete elements. One of the applications of the finite elements developed is for the numerical simulation of composite steel-concrete elements, such as the composite beam formed by a reinforced concrete slab attached to a steel beam using a deformable connection. In this case, the concrete slab and the steel beam are discretized by the flat plate/shell element, and the deformable connection done by the interface elements. In the validation of the implemented elements, we used numerical and experimental results found in the literature, and analytical solutions considering the classical plate theory.
Análise comparativa de sistemas verticais de estabilização e a influência do efeito P-delta no dimensionamento de edifícios de andares múltiplos em aço.
(2002) Tabarelli, Aline; Araújo, Ernani Carlos de; Prestes, José Antônio Soares
Nesse trabalho apresenta-se um estudo comparativo entre os sistemas de estabilizações verticais em pórticos rígidos e os sistemas em treliças em ‘K’ e em ‘X’. A eficiência estrutural é analisada através do relacionamento entre o número de pavimentos com os deslocamentos horizontais, esforços solicitantes e os perfis adotados no dimensionamento dos modelos. Nos sistemas rígidos, os esforços solicitantes e os deslocamentos horizontais são maiores do que nos sistemas contraventados. Nesse caso, leva-se a estruturas mais pesadas e, portanto, menos econômicas. A partir de 24 pavimentos, para se garantirem deslocamentos aceitáveis nos modelos rígidos, a rigidez necessária do sistema fica impraticável. Usaram-se as teorias linear e não-linear (Efeito P-Δ) para análise comparativa dos modelos adotados. Nesse contexto, verificouse que a análise não-linear é fundamental para os modelos com maior número de pavimentos, pois proporciona resultados de esforços e deslocamentos mais coerentes.
Análise da carga térmica de resfriamento e aquecimento por meio de simulação computacional em dois sistemas construtivos : Light Steel Frame e alvenaria de blocos cerâmicos.
(2020) Gallardo, Nuria Perez; Ferreira, Lygia Maria Policarpio; Souza, Tamara Daiane de; Mendes, Múcio André dos Santos Alves; Silva, Mauricio Sanches Duarte; Borges, Alan Monteiro
A otimização de recursos é imperativa na construção civil, cuja finalidade está diretamente relacionada à redução de perdas nos processos e consequente aumento na produtividade. Estes fatores estão diretamente relacionados a eficiência do ambiente construído, onde se destaca o comportamento térmico. O presente trabalho tem como objetivo avaliar a carga térmica de resfriamento e aquecimento de quatro modelos construtivos por meio de simulação computacional, sendo: um modelo construído com sistema de alvenaria de blocos cerâmicos e três modelos em Light Steel Frame (LSF), utilizando diferentes combinações de materiais. A simulação, usando o software Autodesk Revit® 2020, foi realizada sob condições climáticas da cidade de Marabá-PA. Os resultados obtidos mostram um melhor comportamento térmico no método LSF com telha termoacústica, o qual seria capaz de proporcionar melhor conforto térmico aos usuários e potencializar a eficiência energética da edificação.
Análise da estabilidade elástica de treliças espaciais.
(2004) Pinheiro, Leonardo; Silveira, Ricardo Azoubel da Mota
O presente trabalho fornece um estudo da estabilidade de treliças espaciais através da utilização de uma formulação elástica não-linear, baseada no método dos elementos finitos, que leva em consideração os efeitos de segunda ordem e a mudança de geometria da estrutura. Especial atenção é dada ao cálculo da matriz de rigidez, onde tais efeitos são levados em consideração, e à obtenção do vetor de forças internas do elemento. A partir daí, foi realizada uma implementação computacional para que a análise do comportamento de treliças espaciais fosse possível. Ao final desse artigo, através da análise de problemas estruturais encontrados na literatura, pretende-se verificar a eficácia tanto da formulação empregada quanto da implementação computacional realizada.
Análise de fadiga de ligações soldadas de barras de aço tubulares.
(2013) Lage, Carmem Miranda; Sarmanho, Arlene Maria Cunha; Freitas, Marcílio Sousa da Rocha
Nesse trabalho é apresentada uma análise de fadiga de ligações soldadas formadas por perfis estruturais tubulares de aço. É apresentado o procedimento de estimativa de vida útil à fadiga dessas ligações por meio dos métodos da tensão geométrica e da tensão nominal, estabelecidos no CIDECT 8 e Eurocode 3, com abordagem baseada em ciclos de tensão (curvas S-N). A filosofia de projeto associada a esta abordagem é a de vida garantida, que deve proporcionar um nível aceitável de confiabilidade da estrutura sem inspeções periódicas. O modelo analisado foi o de uma ponte metálica treliçada, sendo apresentada uma discussão entre esses dois métodos abordando vantagens e limitações. Os resultados obtidos permitiram determinar qual método é melhor aplicável para uma dada situação de projeto.

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