1,720,955 research outputs found
Estratégias numéricas para simulação de escoamento em meios porosos isotrópicos delgados: benchmark entre Ansys Fluent e OpenFOAM
No full textO presente trabalho realiza um benchmark entre os softwares Ansys Fluent e OpenFOAM para a simulação de escoamento em meios porosos isotrópicos delgados. As simulações monofásicas, turbulentas e em regime permanente foram conduzidas com base em dados experimentais da literatura, de queda de pressão por velocidade de filtração, os quais permitiram ajustar os parâmetros de perdas viscosa e inercial para a modelagem em macroescala do escoamento em um filtro. Os resultados mostraram concordância entre a queda de pressão ajustada e simulada obtidas pelas médias das pressões na entrada e saída do meio poroso. A análise dos contornos de velocidade e pressão estática mostrou-se coerente à dinâmica do escoamento em ambos os softwares com desvios variando de 1,43% a 12,37% para a pressão máxima e de 0,97% a 4,18% para a velocidade máxima. O estudo revelou questões críticas para modelagem de escoamento em meios porosos pelo ajuste dos dados de queda de pressão por velocidade de filtração: os coeficientes de resistência viscosa e inercial calibrados pela regressão dos dados experimentais induziram erros de queda de pressão de 10%, 4,6% e 1%, para as velocidades de filtração de 5, 10 e 15 cm/s, respectivamente; a abordagem utilizada para a validação dos dados baseada nas pressões médias na entrada e saída do meio poroso mostrou-se robusta devido à captura da distribuição da pressão em toda a superfície do filtro; a modelagem da velocidade de entrada, baseado no balanço de massa entre o meio poroso e entrada, resultou em velocidades de filtração numericamente superiores às teóricas, indicando a necessidade de um ajuste iterativo nesta condição para garantir que a velocidade de filtração requerida seja devidamente reproduzida no meio poroso; os altos gradientes de pressão, descolamento da camada limite e zonas de recirculação evidenciaram a necessidade de utilização de modelos de turbulência mais robustos para a captura dos fenômenos envolvidos; e por fim, a abordagem de condição de contorno utilizando o porouBafflePressure apresentou desafios não solucionados de convergência para os cenários testados, impedindo sua viabilidade.The present work performs a benchmark between the softwares Ansys Fluent and OpenFOAM for the simulation of flow in thin isotropic porous media. The single-phase, turbulent, and steady-state simulations were conducted based on experimental data from the literature, namely, pressure drop data by filtration velocity resulting from flow in a filtration box, which allowed adjusting the parameters of viscous and inertial losses for the macroscale modeling of the flow in a filter. The results showed agreement between the adjusted and simulated pressure drop obtained by the pressure averages at the porous medium inlet and outlet. The analysis of velocity and static pressure contours proved to be coherent with the flow dynamics in both softwares with deviations ranging between 1.43% and 12.37% for maximum pressure and between 0.97% and 4.18% for maximum velocity. The study revealed critical issues for modeling flow in porous media through the adjustment of pressure drop data by filtration velocity: the viscous and inertial resistance coefficients calibrated by the regression of experimental data induced pressure drop errors of 10%, 4.6%, and 1%, for filtration velocities of 5, 10, and 15 cm/s, respectively; the approach used for data validation based on the average pressures at the porous medium inlet and outlet proved to be robust due to the capture of the pressure distribution over the entire filter surface; the modeling of the inlet velocity based on the mass balance between the porous medium and inlet, resulted in numerically higher filtration velocities than the theoretical ones, indicating the need for an iterative adjustment in this condition to ensure that the required filtration velocity is properly reproduced in the porous medium; the high-pressure gradients, boundary layer detachment, and recirculation zones evidenced the need for using more robust turbulence models for the capture of the involved phenomena; and finally, the boundary condition approach using porousBafflePressure presented unsolved convergence challenges for the tested scenarios, preventing its viability
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Fluid dynamic study of cyclonic separators inside oil wells through CFD techniques
Get PDFControlling of sand production in oil and gas wells has been a subject of great interest of the oil industry. This process has a direct implication in increasing the costs of production and has been widely described in the literature. Several authors have reported problems due to the sand production in wells that includes: premature waste of equipment, considerable increase in the number of workover operations and the availability of rigs to attend the demand of drilling operations. In this context, this paper focus on simulating efficient separation on 32 swirl tubes geometries as downhole desander device. Firstly, a desander with two vanes was simulated using CFD techniques and compared with experimental data existing in the technical literature. After that, different designs of swirl tubes with different parameters was performed by means of fractional factorial design with two levels in order to perform a sort of most relevant factors. However, the results of the validation test did not show satisfactory results for the particle injection parameters used. Therefore, the fluid dynamic analysis and the application of the method for tangential velocity and pressure drop were performed. According to the results, it was verified that for the five geometrical factors analyzed the external diameter, the number of vaynes and the vortex finder length are the most significant. The most impact on pressure drop are the external diameter, the flow rate and the number of vanes for the pressure drop. Finally, a linear model was proposed for the pressure drop as a function of the eight parameters analyzed and the main interactions between two factors. Among the results, a 110% increase in pressure drop was observed for an increase in the inlet flow from 60 m3 /day to 116 m3 /day.O controle da produção de areia em poços de petróleo e gás tem sido um assunto de grande interesse da indústria do petróleo. A produção de areia tem relação direta com o aumento dos custos de produção destacando-se problemas como o desgaste prematuro de equipamentos, aumento considerável no número de operações de intervenção e principalmente a falta de sondas para as operações de intervenção. Neste contexto, o presente trabalho buscou simular a eficiência de separação em 32 geometrias de separadores tubo-ciclônicos no processo de separação de areia produzida em poços de petróleo. Inicialmente, realizou-se a simulação para o separador tubo-ciclônico de duas hélices cujos dados experimentais estão disponíveis na literatura. Logo após, foram construídas diferentes geometrias deste tipo de separador variando os principais parâmetros geométricos por meio do planejamento fatorial fracionário de dois níveis com o intuito de realizar uma triagem dos fatores que mais relevantes. Contudo, os resultados dos testes de validação não mostram resultados satisfatórios para os parâmetros de injeção de partículas utilizados. Desta forma, foram conduzidas análises do escoamento do fluido para as diferentes geometrias de separadores e aplicação do método para a velocidade tangencial e queda de pressão. De acordo com os resultados, verificou-se que para os cinco fatores geométricos analisados o diâmetro do tubo externo do separador, o número de hélices e o comprimento do vortex finder são os mais significativos. Os fatores que mais influenciaram na queda de pressão foram o diâmetro externo, a vazão de entrada e o número de hélices, sendo mais pronunciada em escoamentos viscosos. Por fim, um modelo baseado no ajuste linear das simulações foi proposto para a queda de pressão em função dos oito parâmetros analisados e das principais interações entre dois fatores. Dentre os resultados, observou-se um aumento de 110% na queda de pressão para um aumento na vazão de entrada de 60 m3/dia para 116 m3/dia
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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