Chronic renal failure is a disease that affects a considerable population percentage that requires the hemodialysis procedure which is a blood filtration. This process is extremely stressful in many cases for the patient, because there is a continuous degradation of vessels and fistulae susceptible to this process due to the alterations of the stress at the blood vessel walls and flow patterns, leading to diseases such as intimal hyperplasia and consequent stenosis. Experimental in vivo researches in this area are very difficult to perform. In this sense computational models become interesting non invasive options to understand what happens to the blood in non viscometric geometries. In this work, we analyse blood flow, through computational modeling, in arteriovenous fistulae used in hemodialysis, using geometries with dimensions close to real ones. Discretization of the governing equations was made through a finite volume technique with the PISO-Pressure Implicit with Splitting of Operators-algorithm, using as a basis the OpenFOAM software platform. Large vessel Newtonian fluid model was used to analyze six possible anastomotic angles (20˚, 25˚, 30˚, 35˚, 40˚, 45˚). To analyze the possibility of stenosis formation caused by hyperplasia, results for wall shear stress, oscillatory shear index (OSI), velocity and local circulation fields were obtained, showing that higher angles presented more secondary flows and larger extensions of stagnation regions near the critical areas of the junctions. Moreover, a range around 25˚ was identified to be the most suitable choice for clinical applications, minimizing possibility of diseases.
A demand for renewable alternatives that would be able to deal with the problems related to well-being is directly linked to the world's growing needs to save energy and reduce environmental costs. For a project implementation addressing these issues, it is essential to know the climatic conditions of the target area. Taking natural ventilation, climatic factors, and renewable alternatives as important sources of comfort, in this work, passive strategies, through the utilization of microclimate elements as well as the location of outside obstacles, were imposed on an initial and specific project. The objective was to introduce obstacles which could interfere in the field of external wind and evaluate whether this outside intervention is able to make changes in indoor air circulation. The wind fields for the studied cases were obtained by computational simulations, and their consequences were analyzed to attain thermal comfort. The method adopted to obtain the wind fields was a Petrov-Galerkin type method, which is a stabilized mixed finite element method of the Navier-Stokes equations considering the incompressibility and formulated in primitive variables, velocity and pressure. The obtained results point to the solutions that promote the increase or decrease of the wind-field intensity.
Resumo. Neste trabalho, uma análise de estabilidade da solução semi-discreta do problema parabólico de difusão do caloré desenvolvida. O problemaé discretizado no espaço usando um método de elementos finitos híbrido estabilizado. Resultando em um sistema de equações diferenciais ordinárias chamado de formulação semi-discreta. Este método, originalmente proposto para problemas elípticos, consiste no acoplamento de problemas locais resolvidos por métodos de Galerkin descontínuo (GD) para a variável primal, temperatura, com um problema global para o multiplicador de Lagrange, queé identificado com o traço da temperatura, impondo continuidade entre os elementos de forma fraca. Esta formulação híbrida possui as boas características dos métodos GD associados como estabilidade, robustez e flexibilidade, mas com complexidade e custo computacional reduzidos. Análiseé feita para a formulação semi-discreta e foram obtidas condições de estabilidade independentes da discretização espacial.
The classic definition of binomial numbers involves factorials, making unfeasible their extension for negative integers. The methodology applied in this paper allows to establish several new binomial numbers extensions for the integer domain, reproduces to integer arguments those extensions that are proposed in other works, and also verifies the results of the usual binomial numbers. To do this, the impossibility to compute factorials with negative integer arguments is eliminated by the replacement of the classic binomial definition to a new one, based on operations recently proposed and, until now, referred to as transformations by the successive sum applied on sequences indexed by integers. By particularizing these operations for the sequences formed and indexed by integers, it is possible to redefine the usual binomial numbers to any integer arguments, with the advantage that the values are more easily computed by using successive additions instead of multiplications, divisions or possibly more elaborate combinations of these operators, which could demand more than one or two sentences to their application.
No abstract
Resumo. Neste trabalho será realizado um estudo de estabilidade da solução totalmente discretizada do problema de condução de calor em regime transiente analisando a influência do parâmetro de estabilização e do ∆t. O problema de condução de caloré caracterizado por equações parabólicas e a variável espacial será discretizada usando um método de elementos finitos híbrido estabilizado combinado com aproximações de diferenças finitas, método de Euler implícito, para variável temporal. O método híbrido estabilizado de elementos finitos consiste no acoplamento de problemas locais, onde a solução da variável primalé obtida, com um problema global para os multiplicadores de Lagrange, identificado como traço da temperatura, e tem a continuidade imposta de forma fraca. A metodologia de implementação utilizada para a resolução do problemaé a denominada Condensação Estática que tem como vantagem o fato de ser mais eficiente do ponto de vista computacional. Os resultados numéricos mostrados comprovam taxasótimas de convergência na norma L 2 (Ω) e não apresentam oscilações espúrias para tempos muito pequenos. Palavras-chave. Elementos Finitos, Métodos Híbridos, Análise de Estabilidade, Equação do Calor IntroduçãoProblemas de condução de calor em regime transiente são comumente representados por equações diferenciais classificadas como parabólicas. As abordagens mais conhecidas são baseadas em formulações semidiscretas de elementos finitos para a aproximação espacial combinadas com esquemas de diferenças finitas para a aproximação temporal. O método de Galerkin clássico, queé usualmente definido de maneira que a aproximação espacial seja contínua entre os elementos da discretização,é bastante empregado para resolver numericamente essa classe de problemas. Contudo, quando esteé o escolhido e o passo do tempoé reduzido com um tamanho de malha fixo, oscilações espaciais espúrias aparecemà medida que o tempo aumenta, poluindo a solução nos tempos iniciais [5]. Com o intuito de 1 daianasb@lncc.br 2 jkfi@lncc.br 3
In this work, we present a mixed stabilized finite element formulation in primitive variables, for an incompressible stationary generalized Stokes problem for pseudoplastic flow governed by the Power-Law model. The mixed formulation is constructed by adding least squares of the governing equations to the classical Galerkin formulation, with continuous interpolations for the velocity and discontinuous interpolations for the pressure. A finite element analysis is presented establishing stability conditions and finding error estimates. Numerical results are presented to show the good performance of this formulation and to confirm the mathematical estimates obtained.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
334 Leonard St
Brooklyn, NY 11211
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.