Análise não-linear de estruturas laminares pelo método dos elementos finitos

ln this work, the finite element method is applied to problems involving the geometrically non-linear behaviour of surface structures, subjected to static and dynamic loads. Two kinds of formulations are studied. ln the first one, through isoparametric degenerated elements, the tridimensional theory of elasticity is directly used. There are no restrictions for the magnitude of the deformations. The other one, derived from the von Kármán strain expressions for large deflections of thin plates, is limited to problems involving small deformations. Results from several analysis are presented. Advantages and limitations of the developed aproximations are discussed, as well as the efficiency of the implemented models.Neste trabalho, aplica-se o método dos elementos finitos à análise do comportamento não-linear geométrico de estruturas laminares, sob ação de cargas estáticas e dinâmicas. Dois tipos de formulação são estudadas. Na primeira, através de elementos degenerados de elementos isoparamétricos, utiliza-se diretamente a teoria da elasticidade tridimensional, não introduzindo restrições quanto à grandeza das deformações. A outra, derivada das equações de von Kármán para grandes deflexões de estruturas delgadas, é específica para problemas de pequenas deformações. Resultados de diversas análises são apresentados. Discutem-se vantagens e limitações das aproximações desenvolvidas e eficiência dos modelos implementados

A double-blind, randomized, comparative study of the use of a combination of uridine triphosphate trisodium, cytidine monophosphate disodium, and hydroxocobalamin, versus isolated treatment with hydroxocobalamin, in patients presenting with compressive neuralgias

CONTEXT: This paper reports on the results of treatment of compressive neuralgia using a combination of nucleotides (uridine triphosphate trisodium [UTP] and cytidine monophosphate disodium [CMP]) and vitamin B(12). OBJECTIVES: To assess the safety and efficacy of the combination of nucleotides (UTP and CMP) and vitamin B(12) in patients presenting with neuralgia arising from neural compression associated with degenerative orthopedic alterations and trauma, and to compare these effects with isolated administration of vitamin B(12). METHODS: A randomized, double-blind, controlled trial, consisting of a 30-day oral treatment period: Group A (n=200) receiving nucleotides + vitamin B(12,) and Group B (n=200) receiving vitamin B(12) alone. The primary study endpoint was the percentage of subjects presenting pain visual analog scale (VAS) scores ≤20 at end of study treatment period. Secondary study endpoints included the percentage of subjects presenting improvement ≥5 points on the patient functionality questionnaire (PFQ); percentage of subjects presenting pain reduction (reduction in VAS scores at study end in relation to pretreatment); and number of subjects presenting adverse events. RESULTS: The results of this study showed a more expressive improvement in efficacy evaluations among subjects treated with the combination of nucleotides + vitamin B(12), with a statistically significant superiority of the combination in pain reduction (evidenced by VAS scores). There were adverse events in both treatment groups, but these were transitory and no severe adverse event was recorded during the study period. Safety parameters were maintained throughout the study in both treatment groups. CONCLUSION: The combination of uridine, cytidine, and vitamin B(12) was safe and effective in the treatment of neuralgias arising from neural compression associated with degenerative orthopedic alterations and trauma

Modelling and optimisation of the operation of a radiant warmer

This paper presents numerical calculations of the temperature field obtained for the case of a neonate placed under a radiant warmer. The results of the simulations show a very non-uniform temperature distribution on the skin of the neonate, which may cause increased evaporation leading to severe dehydration. For this reason, we propose some modifications on the geometry and operation of the radiant warmer, in order to make the temperature distribution more uniform and prevent the high temperature gradients observed on the surface of the neonate. It is concluded that placing a high conductivity blanket over the neonate and introducing additional screens along the side of the mattress, thus recovering the radiation heat escaping through the side boundaries, helped providing more uniform temperature fields.The European Union for the Marie Curie Fellowship grant awarded to the Centre for CFD, University of Leeds

A combined study of heat and mass transfer in an infant incubator with an overhead screen

The main objective of this study is to investigate the major physical processes taking place inside an infant incubator, before and after modifications have been made to its interior chamber. The modification involves the addition of an overhead screen to decrease radiation heat losses from the infant placed inside the incubator. The present study investigates the effect of these modifications on the convective heat flux from the infant’s body to the surrounding environment inside the incubator. A combined analysis of airflow and heat transfer due to conduction, convection, radiation and evaporation has been performed, in order to calculate the temperature and velocity fields inside the incubator before and after the design modification. Due to the geometrical complexity of the model, Computer-Aided Design (CAD) applications were used to generate a computer-based model. All numerical calculations have been performed using the commercial Computational Fluid Dynamics (CFD) package FLUENT, together with in-house routines used for managing purposes and User-Defined Functions (UDFs) which extend the basic solver capabilities. Numerical calculations have been performed for three different air inlet temperatures: 32, 34 and 36ºC. The study shows a decrease of the radiative and convective heat losses when the overhead screen is present. The results obtained were numerically verified as well as compared with results available in the literature from investigations of dry heat losses from infant manikins

CFD modelling of a two-phase closed thermosyphon charged with R134a and R404a

This paper examines the application of CFD modelling to simulate the two-phase heat transfer mechanisms in a wickless heat pipe, also called a thermosyphon. Two refrigerants, R134a and R404a, were selected as the working fluids of the investigated thermosyphon. A CFD model was built to simulate the details of the two-phase flow and heat transfer phenomena during the start-up and steady-state operation of the thermosyphon. The CFD simulation results were compared with experimental measurements, with good agreement obtained between predicted temperature profiles and experimental temperature data, thus confirming that the CFD model was successful in reproducing the heat and mass transfer processes in the R134a and R404a charged thermosyphon, including the pool boiling in the evaporator section and the liquid film in the condenser section

UMA IMPLEMENTAÇÃO DO MEC SIMÉTRICO DE GALERKIN PARA PROBLEMAS DE ELASTICIDADE 2D

O Método dos Elementos de Contorno (MEC) pode ser derivado por diferentes metodologias, resultando em implementações computacionais distintas, que se baseiam em reduzir as equações integrais de contorno contínuas em sistemas de equações lineares. A formulação clássica do MEC é conhecida como Método da Colocação, onde se procura satisfazer as equações integrais de contorno de forma forte, diretamente em nós específicos do contorno do modelo, usualmente, os próprios nós de discretização do problema. Em contraste, no Método de Galerkin procura-se satisfazer as equações integrais de contorno de forma fraca. A estratégia utilizada pelo método consiste em aplicar a Técnica de  resíduos Ponderados de Galerkin às equações integrais de contorno, distribuindo-se o erro cometido pela aproximação da melhor forma possível. Pode-se ainda, fazendo uso das equações hipersingulares de contorno, reduzir as equações integrais de contorno a um sistema simétrico de equações lineares. Denomina-se essa estratégia de Método Simétrico de Galerkin. Apresenta-se no trabalho os principais passos para a implementação numérica do MEC Simétrico de Galerkin para problemas de elasticidade linear bidimensional. São apresentadas as estratégias para obtenção do sistema de equações simétrico, construção de uma matriz de rigidez simétrica global e as técnicas utilizadas no cálculo das integrais singulares decorrentes deste método

Multiscale model of the role of grain boundary structures in the dynamic intergranular failure of polycrystal aggregates

National Council for Scientific and Technological Development-CNPq, Brazil (grant numbers: 312493/2013-4, 154283/2014-2); the Coordination for the Improvement of Higher Education Personnel-CAPES, Brazil (grant number: 88882.329019/2019-01

Numerical simulation of turbulent flow in a channel containing a small slot

A three-dimensional unsteady simulation was carried out to predict the main features of the turbulent flow inside a closed channel connected to a lateral slot. The incompressible turbulent flow was modelled using a hybrid Detached Eddy Simulation (DES), that uses an LES/URANS approach to predict the turbulence. The calculations were performed using ANSYS® CFX. In this work the main channel has a size of 180 mm x 136.20 mm. The small subchannel is characterized by its deepness, p = 77 mm and width, d = 10 mm. The Reynolds number, based on the hydraulic-diameter, Dh, the bulk velocity, and the kinematic viscosity, ν, in the main channel was Re = 2.25 × 105. Inside the small slot the velocity distribution was found to depart from the law of the wall and the normal Reynolds stresses, View the MathML sourceu′u′¯ and View the MathML sourcev′v′¯, were found to dominate the mixing process. Velocity time-traces extracted at locations as far as y/p = 1.125 inside the gap evidenced the presence of large eddies travelling inside the small channel. It was shown that periodic streamwise boundary conditions can be applied to this problem, and good results were obtained by using a channel length that was approximately twice the wavelength of the experimentally observed coherent structures. The results were found to be in fair agreement with the results presented in Meyer and Rehme (1994), though a certain lack of information on turbulence in single channels connected to a gap still remains