Resin Transfer Molding (RTM) is a polymer composite processing technique widely used in the aeronautics and automotive sectors. This paper describes the numerical simulation of the RTM process where Darcy’s law was used for the mathematical formulation of the problem. A control volume finite element method was used for the determination of pressure gradients inside the mold, and a geometric reconstruction algorithm is used for the resin flow-front determination. Permeability of the medium was considered either a constant or a two dimensional tensor. The application was validated by direct comparison with literature data and good qualitative and quantitative agreement was obtained. The finite volume method was built to be used with a two-dimensional unstructured grid, hence allowing the analysis of complex geometries. The results showed that the proposed methodology is fully capable of predicting resin flow advancement in a multi-layer (with distinct physical properties) reinforced media.

Computational Fluid Dynamics (CFD) is widely used by polymer processing industries in order to evaluate polymeric fluid flows. A successful computational code must provide reliable predictions (modeling) in a fast and efficient way (simulation). In this work, a new approach to solve the governing equations of viscoelastic fluid flows is proposed. It is based on the finite-volume method with collocated arrangement of the variables, using high-order approximations for the linear and nonlinear average fluxes in the interfaces and for the nonlinear terms obtained from the discretization of the constitutive equations. The approximations are coupled to the Weighted Essentially Non-Oscillatory (WENO) scheme to avoid oscillations in the solution. The Oldroyd-B model is used to describe the rheological behavior of the viscoelastic fluid. The average values of the variables in the volumes are used during the resolution, and the point values are recovered in the post-processing step by deconvolution of the average values. The nonlinear system, resulting from the discretization of the equations, is solved simultaneously using a Newton-like method. The obtained solutions are oscillation-free and accurate, demonstrated by the application on a classic problem in computational fluid dynamics...

Desde os primeiros estudos numéricos sobre lubrificação em mancais hidrodinâmicos até a atualidade, existiram relativamente poucos trabalhos abordando o problema através do método dos volumes finitos. Na verdade, a maioria dos estudos, na área de lubrificação, utiliza a equação de Reynolds e o método das diferenças finitas para estabelecer o campo de pressão gerado no filme de óleo, mesmo sendo este tipo de abordagem inviável em certos casos, pois para geometrias mais complexas, ou com certas condições dinâmicas do sistema, a qualidade da discretização e a consistência dos resultados gerados pela equação de Reynolds se mostram insuficientes. Sendo assim, este trabalho trata da análise do campo de pressão em um filme gerado através do efeito hidrodinâmico em um mancal radial cilíndrico plano. Para tanto, o fluido de lubrificação é colocado em condição isotérmica e em regime de escoamento laminar. Para avaliar o campo de pressão é desenvolvido um algoritmo que determina a solução através do método dos volumes finitos para a equação simplificada de Reynolds em um domínio com duas dimensões, e segue com as seguintes etapas: construção da malha, integração das equações dentro dos volumes...

A simulação numérica computacional é nos dia de hoje frequentemente aplicada na elaboração de projetos ou análise dos processos de conformação plástica dos metais. A extrusão de metais é um dos principais processos de conformação plástica e largamente aplicado na fabricação de produtos e peças na indústria metal-mecânica. Tradicionalmente, essas análises são feitas utilizando o Método dos Elementos Finitos. Entretanto, há um aumento no interesse dos pesquisadores na utilização do Método dos Volumes Finitos para este fim. A literatura sugere que o escoamento na extrusão de metais pode ser analisado pela formulação do escoamento plástico (flow Formulation). No qual, pode-se assumir como o escoamento de um fluido incompressível e viscoso. Essa hipótese pode ser assumida já que o processo de extrusão é um processo isocórico. O método MacCormack é geralmente aplicado para simular os escoamentos de fluidos compressíveis pelo Método do Volumes Finitos. No escoamento de um fluido incompressível ou no escoamento de metal não existe uma equação para a evolução da variável pressão, sendo necessário a utilização de um método de acoplamento entre a pressão e a velocidade. Este trabalho trata da apresentação de um novo esquema numérico para a determinação de informações sobre o escoamento de um fluido incompressível e viscoso e sobre o escoamento de metal em um processo de extrusão direta...

Neste trabalho foi desenvolvido um novo programa computacional em Fortran 90, com o objetivo de obter soluções numéricas de um sistema de equações diferenciais parciais de Magnetohidrodinâmica Relativística, com gravitação pré-determinada (GRMHD), capaz de simular a formação de jatos relativísticos desde a acreção de disco de matéria até sua ejeção. De início fez-se um estudo sobre métodos numéricos de Volumes Finitos Unidimensionais, a saber método Lax-Friedrichs, Lax-Wendroff, Nessyahu-Tadmor e métodos de Godunov dependentes de problemas de Riemann, aplicados nas equações de Euler com o intuito de verificar as suas principais características e de efetuar comparações entre aqueles métodos. Em seguida implementou-se os métodos de Volumes Finitos Centrados Lax-Friedrichs e Nessyahu-Tadmor, que são esquemas numéricos que possuem uma formulação sem separação dimensional e livres de resolvedores de problemas de Riemann, mesmo em duas ou mais dimensões espaciais; neste ponto, já aplicados nas equações de GRMHD. Um método Lax-Wendroff com Runge-Kutta de ordem 3, com a propriedade de ser Valor Total Decrescente (TVD) no tempo e com separação dimensional, também foi aplicado no mesmo problema. Por fim...

The time discretization of a very high-order finite volume method may give rise to new numerical difficulties resulting into accuracy degradations. Indeed, for the simple one-dimensional unstationary convection-diffusion equation for instance, a conflicting situation between the source term time discretization and the boundary conditions may arise when using the standard Runge-Kutta method. We propose an alternative procedure by extending the Butcher Tableau to overcome this specific difficulty and achieve fourth-, sixth- or eighth-order of accuracy schemes in space and time. To this end, a new finite volume method is designed based on specific polynomial reconstructions for the space discretization, while we use the Extended Butcher Tableau to perform the time discretization. A large set of numerical tests has been carried out to validate the proposed method.; Fundação para a Ciência e a Tecnologia (FCT)

A new solver for the Stokes equations based on the finite volume method is proposed using very accurate polynomial reconstruction to provide a 6th-order scheme. We face two main difficulties: the gradient-divergence duality where the divergence free condition will impose the pressure gradient, and on the other hand, we assume that the domain has a regular curved boundary. The last point implies that a simple approximation of the boundary using piecewise segment lines dramatically reduces the scheme accuracy to at most a second-order one. We propose a new and simple technology which enables to restore the full scheme accuracy based on a specific polynomial reconstruction only using the Gauss points of the curved boundary and does not require any geometrical transformation.; Fundação para a Ciência e a Tecnologia (FCT); This research was financed by FEDER Funds through Programa Operational Fatores de Competitividade — COMPETE and by Portuguese Funds FCT — Fundação para a Ciência e a Tecnologia, within the Projects PEst-C/MAT/UI0013/2014, PTDC/MAT/121185/2010 and FCT-ANR/MAT-NAN/0122/2012

Computational Fluid Dynamics (CFD) is widely used by polymer processing industries in order to evaluate polymeric fluid flows. A successful computational code must provide reliable predictions (modeling) in a fast and efficient way (simulation). In this work, a new approach to solve the governing equations of viscoelastic fluid flows is proposed. It is based on the finite-volume method with collocated arrangement of the variables, using high-order approximations for the linear and nonlinear average fluxes in the interfaces and for the nonlinear terms obtained from the discretization of the constitutive equations. The approximations are coupled to the Weighted Essentially Non-Oscillatory (WENO) scheme to avoid oscillations in the solution. The Oldroyd-B model is used to describe the rheological behavior of the viscoelastic fluid. The average values of the variables in the volumes are used during the resolution, and the point values are recovered in the post-processing step by deconvolution of the average values. The nonlinear system, resulting from the discretization of the equations, is solved simultaneously using a Newton-like method. The obtained solutions are oscillation-free and accurate, demonstrated by the application on a classic problem in computational fluid dynamics...

This work deals with a new numerical methodology to solve the Navier-Stokes equations based on a finite volume method applied to structured meshes with co-located grids. High-order schemes used to approximate advective, diffusive and non-linear terms, connected with multiblock partition techniques, are the main contributions of this paper. Combination of these two techniques resulted in a computer code that involves high accuracy due the high-order schemes and great flexibility to generate locally refined meshes based on the multiblock approach. This computer code has been able to obtain results with higher or equal accuracy in comparison with results obtained using classical procedures, with considerably less computational effort.

In this work, computer simulation results of steady incompressible flow in a 2-D square lid-driven cavity up to Reynolds number (Re) 65000 are presented and compared with those of earlier studies. The governing flow equations are solved by using the finite volume approach. Quadratic upstream interpolation for convective kinematics (QUICK) is used for the approximation of the convective terms in the flow equations. In the implementation of QUICK, the deferred correction technique is adopted. A non-uniform staggered grid arrangement of 768x768 is employed to discretize the flow geometry. Algebraic forms of the coupled flow equations are then solved through the iterative SIMPLE (Semi-Implicit Method for Pressure-Linked Equation) algorithm. The outlined computational methodology allows one to meet the main objective of this work, which is to address the computational convergence and wiggled flow problems encountered at high Reynolds and Peclet (Pe) numbers. Furthermore, after Re > 25000 additional vortexes appear at the bottom left and right corners that have not been observed in earlier studies.

In recent years, there has been a significant level of research on the application of unstructured mesh methods to the simulation of a variety of engineering and scientific problems. Great progress has been achieved in such area and one of the most successful methodologies consists on the use of the Finite Volume Method (FVM). The unstructured FV formulation is very flexible to deal with any kind of control volume and therefore any kind of unstructured meshes, which are particularly important when complex geometries or automatic mesh adaptation are required. In this article, an unstructured finite volume vertex centered formulation, which was implemented using an edge-based data structure, is deduced and detailed for the solution of heat conduction problems. The numerical formulation is initially described considering a tri-dimensional model and latter particularized for bi-dimensional applications using triangular meshes. The presented procedure is very flexible and efficient to solve potential problems. It can also be extended to deal with a broader class of applications, such as models involving convection-diffusion-reaction terms, after considering the appropriate discretization of the convection-type term. In order to demonstrate the potentiality of the method...

The laminar fully developed free surface flow in a helical channel with finite pitch and rectangular section is modeled. The mass and momentum conservation equations are written in a local orthogonal system and solved numerically using the finite volume method. The free surface position, determined using the height of liquid method, compares favorably against the experimental data. The main and secondary velocity fields are determined as well as the friction factor for Reynolds number ranging from 352 to 856.

This study analyzes the heat transfer in human eyes following implantation of retinal prostheses using an axisymmetric formulation of the Finite Volume Method. The model used consisted of a vertex centered unstructured grid finite volume method in an edge-based data structure and an explicit time integration. The results of the finite volume thermal analysis in ocular tissues were determined in the presence of two types of retinal implants: subretinal and epiretinal. For the subretinal device, the maximum temperature reached in the retina was 36.78°C (309.78 K) and the irreversible thermal damage occurred at 200 days. In the case of the epiretinal implant, the maximum temperature reached at the retinal/chip interface was 36.92°C (309.92 K) and the irreversible thermal damage occurred at 180 days. Our results indicate that tin spite of its higher dissipation power, the epiretinal implant produces thermal damages similar to that caused by the subretinal implant. The computational tool which was developed was able to effectively calculate temperature profiles and thermal damage values to retinal implants and is also capable to calculate temperature profile in any other geometry of interest, for example with other types s of external thermal source like laser beans.

Resin Transfer Molding (RTM) is a polymer composite processing technique widely used in the aeronautics and automotive sectors. This paper describes the numerical simulation of the RTM process where Darcy???s law was used for the mathematical formulation of the problem. A control volume finite element method was used for the determination of pressure gradients inside the mold, and a geometric reconstruction algorithm is used for the resin flow-front determination. Permeability of the medium was considered either a constant or a two dimensional tensor. The application was validated by direct comparison with literature data and good qualitative and quantitative agreement was obtained. The finite volume method was built to be used with a two-dimensional unstructured grid, hence allowing the analysis of complex geometries. The results showed that the proposed methodology is fully capable of predicting resin flow advancement in a multi-layer (with distinct physical properties) reinforced media.

A numerical method suitable for wave propagation problems in complex geometries is developed for simulating dynamic earthquake ruptures with realistic friction laws. The numerical method couples an unstructured, node-centered finite volume method to a structured, high order finite difference method. In this work we our focus attention on 2-D antiplane shear problems. The finite volume method is used on unstructured triangular meshes to resolve earthquake ruptures propagating along a nonplanar fault. Outside the small region containing the geometrically complex fault, a high order finite difference method, having superior numerical accuracy, is used on a structured grid. The finite difference method is coupled weakly to the finite volume method along interfaces of collocated grid points. Both methods are on summation-by-parts form. The simultaneous approximation term method is used to weakly enforce the interface conditions. At fault interfaces, fault strength is expressed as a nonlinear function of sliding velocity (the jump in particle velocity across the fault) and a state variable capturing the history dependence of frictional resistance. Energy estimates are used to prove that both types of interface conditions are imposed in a stable manner. Stability and accuracy of the numerical implementation are verified through numerical experiments...

The design of efficient, simple, and easy to code, second-order finite volume methods is an important challenge to solve practical problems in physics and in engineering where complex and very accurate techniques are not required. We propose an extension of the original Frink's approach based on a cell-to-vertex interpolation to compute vertex values with neighbor cell values. We also design a specific scheme which enables to use whatever collocation point we want in the cells to overcome the mass centre point restrictive choice. The method is proposed for two- and three-dimension geometries and a second-order extension time-discretization is given for time-dependent equation. A large number of numerical simulations are carried out to highlight the performance of the new method.; Fundação para a Ciência e a Tecnologia (FCT)

Resin Transfer Molding (RTM) is a polymer composite processing technique widely used in the aeronautics and automotive sectors. This paper describes the numerical simulation of the RTM process where Darcy's law was used for the mathematical formulation of the problem. A control volume finite element method was used for the determination of pressure gradients inside the mold, and a geometric reconstruction algorithm is used for the resin flow-front determination. Permeability of the medium was considered either a constant or a two dimensional tensor. The application was validated by direct comparison with literature data and good qualitative and quantitative agreement was obtained. The finite volume method was built to be used with a two-dimensional unstructured grid, hence allowing the analysis of complex geometries. The results showed that the proposed methodology is fully capable of predicting resin flow advancement in a multi-layer (with distinct physical properties) reinforced media.

A new very high-order finite volume method to solve problems with harmonic and biharmonic operators for one- dimensional geometries is proposed. The main ingredient is polynomial reconstruction based on local interpolations of mean values providing accurate approximations of the solution up to the sixth-order accuracy. First developed with the harmonic operator, an extension for the biharmonic operator is obtained, which allows designing a very high-order finite volume scheme where the solution is obtained by solving a matrix-free problem. An application in elasticity coupling the two operators is presented. We consider a beam subject to a combination of tensile and bending loads, where the main goal is the stress critical point determination for an intramedullary nail.

In this research, a new explicit 2D numerical solution is presented to compute the temperature field which is caused due to hydration and thermal conductivity by the Galerkin finite volume method on unstructured meshes of triangular elements. The concrete thermal properties vary, based on the temperature variation and the age of the concrete in the developed model. A novel method for imposing natural boundary conditions is introduced that is suitable for the Galerkin finite volume method solution on unstructured meshes of triangular elements. In addition, the thermal contact is considered at the concrete-rock foundation interface to achieve more realistic simulations in this section. In this work we present the comparison of the thermal analysis numerical results of a plane wall, which had different thermal boundary conditions applied to its edges, with its analytical solution to assess the accuracy and efficiency of the developed model. The applicability of the developed numerical algorithm for thermal analysis is presented by the solution of thermal fields during gradual construction of a typical mass concrete structure.

In this research, a 2D matrix-free Galerkin finite volume method on the unstructured meshes of triangular elements is utilised to compute thermal stress fields resulting from the predefined transient temperature distribution in a mass concrete structure (dam wall). In the developed numerical model, the convergence of the force equilibrium equations are achieved via some iterative solutions for each given computed temperature field. Since the mechanical properties of concrete may vary over time due to concrete ageing, the presented numerical model considers the variation of mechanical properties corresponding to the degree of concrete hydration and concrete temperature. In addition, the geometry of the dam wall and foundation is not considered integrated any longer, so the mechanical contact is considered at concrete-rock foundation interface to achieve more realistic simulations of the strain-stress fields in this part. In this work we present the comparison of thermal stress analysis numerical results (of a clamped plane which is exposed to constant temperature) with the results of finite element-based ALGOR software to assess the accuracy and efficiency of the developed model, and prove that the results correlate well. As an application of the developed model for a real-world problem...