Valdemir Souza Ferreira - Academia.edu (original) (raw)

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Papers by Valdemir Souza Ferreira

Revista de Engenharia Térmica, 2003

This work shows an extension of the generalized Peaceman and Rachford alternating-direction impli... more This work shows an extension of the generalized Peaceman and Rachford alternating-direction implicit (ADI) scheme for simulating two-dimensional fluid flows at low Reynolds numbers. The conservation equations are solved in stream function - vorticity formulation. We compare the ADI and generalized ADI schemes, and show that the latter is more efficient to simulate a creeping flow. Numerical results demonstrating the applicability of this technique are also presented.

TEMA - Tendências em Matemática Aplicada e Computacional, 2005

The present work is concerned with a study of numerical schemes for solving two-dimensional time-... more The present work is concerned with a study of numerical schemes for solving two-dimensional time-dependent incompressible free-surface fluid flow problems. The primitive variable flow equations are discretized by the finite difference method. A projection method is employed to uncouple the velocity components and pressure, thus allowing the solution of each variable separately (a segregated approach). The diffusive terms are discretized by Implicit Backward and Crank-Nicolson schemes, and the non-linear advection terms are approximated by the high order upwind VONOS (Variable-Order Non-oscillatory Scheme) technique. In order to improved numerical stability of the schemes, the boundary conditions for the pressure field at the free surface are treated implicitly, and for the velocity field explicitly. The numerical schemes are then applied to the simulation of the Hagen-Poiseuille flow, and container filling problems. The results show that the semi-implicit techniques eliminate the stability restriction in the original explicit GENSMAC method.

TEMA - Tendências em Matemática Aplicada e Computacional, 2004

Implicit schemes are studied with the purpose of introducing them in the two-dimensional GENSMAC ... more Implicit schemes are studied with the purpose of introducing them in the two-dimensional GENSMAC method, for the numerical solution of unsteady newtonian incompressible flows. By using the fractional-step approach, the Freeflow2D simulation system is employed to solve the conservation equations. The viscous terms in the Navier-Stokes equations are implicitly treated via the Implicit Backward (IR), Crank-Nicolson (CN) and Adams-Bashforth/Crank-Nicolson (AB/CN) schemes. The convective terms are explicitly treated by the upwind differencing Variable Order Non-Oscillatory Scheme (VONOS) scheme. For channel and impinging jet flows, the numerical techniques are robust and produce results that compare very well with the analytical solutions.

Journal of Sol-Gel Science and Technology, 2010

The fluid flow of the liquid phase in the sol-geldip-coating process for SnO 2 thin film depositi... more The fluid flow of the liquid phase in the sol-geldip-coating process for SnO 2 thin film deposition is numerically simulated. This calculation yields useful information on the velocity distribution close to the substrate, where the film is deposited. The fluid modeling is done by assuming Newtonian behavior, since the linear relation between shear stress and velocity gradient is observed. Besides, very low viscosities are used. The fluid governing equations are the Navier-Stokes in the two dimensional form, discretized by the finite difference technique. Results of optical transmittance and X-ray diffraction on films obtained from colloidal suspensions with regular viscosity, confirm the substrate base as the thickest part of the film, as inferred from the numerical simulation. In addition, as the viscosity increases, the fluid acquires more uniform velocity distribution close to the substrate, leading to more homogenous and uniform films.

Journal of Physics: Conference Series, 2011

The correct modeling for processes involving convection, without introducing excessive artificial... more The correct modeling for processes involving convection, without introducing excessive artificial damping while retaining high accuracy, stability, boundedness and simplicity of implementation continues being nowadays a challenging task for CFD practitioners. The objective of this study is to present and evaluate the performance of two new upwinding schemes, namely SDPUS-C1 and EPUS, for nonlinear convection term discretization. Both SDPUS-C1 and EPUS schemes satisfy the TVD principle of Harten and are based on the NVD formulation of Leonard. Firstly, a description of the schemes is presented and then the numerical results are provided for one-and two-dimensional hyperbolic conservation laws. Finally, as an application, the SDPUS-C1 and EPUS schemes are employed for the simulation of two-dimensional incompressible fluid flows involving moving free surfaces. The numerical experiments show that the proposed upwinding schemes perform very well.

Experimental Cell Research, 2011

Activin A and transforming growth factor-β1 (TGF-β1) belong to the same family of growth and diff... more Activin A and transforming growth factor-β1 (TGF-β1) belong to the same family of growth and differentiation factors that modulate vascular lesion formation in distinct ways, which we wish to understand mechanistically. Methods and results: We investigated the expression of cell-surface receptors and activation of Smads in human vascular smooth muscle cells (SMCs) and demonstrated that activin receptor-like kinase-1 (ALK-1), ALK-4, ALK-5 and endoglin are expressed in human SMCs. As expected, TGF-β1 activates Smad1 and Smad2 in these cells. Interestingly, activin A also induces phosphorylation of both Smads, which has not been reported for Smad1 before. Transcriptome analyses of activin A and TGF-β1 treated SMCs with subsequent Gene-Set Enrichment Analyses revealed that many downstream gene networks are induced by both factors. However, the effect of activin A on expression kinetics of individual genes is less pronounced than for TGF-β1, which is explained by a more rapid dephosphorylation of Smads and p38-MAPK in response to activin A. Substantial differences in expression of fibronectin, alpha-V integrin and total extracellular collagen synthesis were observed. Conclusions: Genome-wide mRNA expression analyses clarify the distinct modulation of vascular lesion formation by activin A and TGF-β1, most significantly because activin A is non-fibrotic.

Computational & Applied Mathematics, 2012

This paper reports experiments on the use of a recently introduced advection bounded upwinding sc... more This paper reports experiments on the use of a recently introduced advection bounded upwinding scheme, namely TOPUS (Computers & Fluids 57 (2012) 208-224), for flows of practical interest. The numerical results are compared against analytical, numerical and experimental data and show good agreement with them. It is concluded that the TOPUS scheme is a competent, powerful and generic scheme for complex flow phenomena.