Gustavo Buscaglia | Universidade de São Paulo (original) (raw)

Papers by Gustavo Buscaglia

This work aims the study of finite element methods discretized in dynamic meshes in order to simu... more This work aims the study of finite element methods discretized in dynamic meshes in order to simulate multiphase flow, particularly flows involving the agglomeration of dense packs of drops. The equations involved will be treated in an arbitrary lagrangian-eulerian framework (ALE) [1]. The numerical challenges range from the correct representation of interfaces, passing through the maintainability of the computer mesh, until the adequate representation of coalescence phenomena. We start considering rigid bodies surrounded by a newtonian fluid instead of drops [2, 3], situation that is modeled by the NavierStokes equations for the continuous phase, coupled with rigid bodies dynamics. This approach gives the possibility of analyzing rigid bodies collision processes, for the purpose of developping numerical coalescence simulation methodologies.

A ﬁnite element space with embedded discontinuities has been recently introduced by the authors (... more A ﬁnite element space with embedded discontinuities has been recently introduced by the authors (R. Ausas et al, Comp. Meth. Appl. Mech. Engrg, 199:1019-1031, 2009; see also Mecanica Computacional 28:1131-1148, 2009). This space has the same unknowns as the linear, continuous ﬁnite element space, but is locally modiﬁed to accommodate discontinuities at an arbitrary interface, not coincident with the element boundaries. The motivation comes from Eulerian treatment of surface tension problems, in which there is a pressure jump at the interface. It has been shown both numerically and theoretically (G. Buscaglia and A. Agouzal, CILAMCE, 2009) that this space has good interpolation properties. Numerical examples have also shown that, when used as pressure space in a ﬁnite element formulation of the Navier-Stokes equations, the proposed space leads to accurate results. This suggests that inf–sup stability conditions are satisﬁed, but they are very hard to prove because the space depends o...

This mini-symposium is devoted to free-surface, moving-boundary and multi-phase flows. We invite ... more This mini-symposium is devoted to free-surface, moving-boundary and multi-phase flows. We invite all researchers working in the area to present their recent developments and applications. The main topics are: - Numerical algorithms for describing free-surface, moving-boundary and multi-phase flows. - Interface-tracking, interface-capturing and diffuse-interface techniques. - Fixed/moving mesh and meshfree formulations. - Volume of fluid, level-set, and Eulerian-Lagrangian methods. - Surface reconstruction and renormalization operators. - Surface tension, capillarity and transport of surfactants. - Wetting/Drying of surfaces. - Experimental validation. - Scientific and technological applications. These topics cover relevant areas of computational mechanics knowledge with many recent developments.

This work presents a numerical scheme to improve the velocity ﬁeld used to transport the level se... more This work presents a numerical scheme to improve the velocity ﬁeld used to transport the level set function in two phase liquid–gas ﬂows. Since the material properties (density and viscosity) are discontinuous at the moving interface, the velocity ﬁeld that results from the Navier-Stokes solver is inaccurate close to the interface, leading to non negligible errors in the transport of the level set function. The methodology is based on the resolution of an elasticity-like partial differential equation to compute an improved velocity ﬁeld, being thus much easier to implement in standard ﬁnite element codes than other geometrical extrapolation methodologies. In the computation, only the physical velocity on the liquid side is considered, since it governs the dynamics. The improved velocity ﬁeld is then exclusively used for the transport of the level set function. Though no incompressibility constraint is imposed to the extrapolated velocity, numerical evidence shows that the method imp...

En este trabajo se describen varios problemas actuales de modelado y diseno optimo de dispositivo... more En este trabajo se describen varios problemas actuales de modelado y diseno optimo de dispositivos lubricados counidos incompresibles. Se presentan las ecuaciones de gobierno y los modelos matematicos del fenomeno de cavitacion, que es crucial para cojinetes circunferenciales (e.g.; bujes), asi como los metodos numericos utilizados. Se incluye tambien una breve revision de resultados teoricos y numericos recientes. Por ultimo, se reportan tres resultados novedosos: En primer lugar, una demostracion numerica de reduccion de la friccion mediante texturacion de la superficie. Se trata de la primera evidencia numerica obtenida con metodos conservativos, e indica que la mencionada reduccion solo es posible cuando la carga aplicada es de baja intensidad. En segundo lugar, una evaluacion de formas obtenidas por diseno optimo en las condiciones del ensayo NMVEG, de control de emisiones y consumo de combustibles para vehiculos comercializados en la Union Europea. En tercer lugar, realizamos ...

In the presence of strong heterogeneities, it is well known that the use of explicit schemes for ... more In the presence of strong heterogeneities, it is well known that the use of explicit schemes for the transport of species in a porous medium suffers from severe restrictions on the time step. This has led to the development of implicit schemes that are increasingly favoured by practitioners for their computational efficiency. The transport equation requires knowledge of the velocity field, which results from an elliptic problem (Darcy problem) that is the most expensive part of the computation. When considering large reservoirs, a cost-effective way of approximating the Darcy problems is using multiscale domain decomposition (MDD) methods. They allow for the pressure and velocity fields to be computed on coarse meshes (large scale), while detailed basis functions are defined locally, usually in parallel, in a much finer grid (small scale). In this work we adopt the Multiscale Robin Coupled Method (MRCM, [Guiraldello, et al., J. Comput. Phys., 355 (2018) pp. 1-21], [Rocha, et al., J....

In order to develop a single-whole red blood cell model it is necessary to model the interaction ... more In order to develop a single-whole red blood cell model it is necessary to model the interaction between the lipidic bilayer and the cytoskeleton. To minimic these interactions is a current and open problem with important applications in medicine. In this work we provide a mathematical formulation of a soft-body adhesion model in presence of a continuos lipidic membrane.

Journal of the Brazilian Society of Mechanical Sciences and Engineering

Resumo. Métodos cuja ordem formal de convergênciaé alta (≥ 2) tem bastante popularidade na soluçã... more Resumo. Métodos cuja ordem formal de convergênciaé alta (≥ 2) tem bastante popularidade na solução numérica de leis de conservação hiperbólicas, em particular da equação de Buckley-Leverett que descreve escoamentos bifásicos em meios porosos. Porém, nas aplicações, as hipóteses que permitem provar a convergência de alta ordem são raramente satisfeitas. O objetivo dessa contribuiçãoé mostrar, através de análises empíricas, o efeito da regularidade da solução sobre a ordem de convergência. Em particular, mostrar que (a) a presença de ondas de choque destrói a alta ordem quando a convergênciaé medida em normas L p (Ω), com p ≥ 1 mas não na norma dual Lip (Ω); e que (b) a presença de ondas de rarefaçãoé mais prejudicial, levando os métodos a primeira ordem de convergência inclusive na norma Lip (Ω). Essas observações fazem com que a ordem formal do método nunca se realize nos casos de aplicação. A escolha do método precisa então de estudos empíricos de convergência para problemas realistas, que permitam avaliar a precisão efetiva. Um estudo 2D desse tipo, com propriedades altamente heterogêneas,é reportado na segunda parte do trabalho. Nele,é observada ordem de convergência menor que um (O(h 1/2)) para métodos de ordem formal 1 (Godunov, Rusanov) e ordem O(h) para suas variantes de ordem formal 2, verificando-se uma vantagem de precisão para essesúltimos tanto se implementados com limitador minmod quanto com limitador superbee.

TEMA (São Carlos)

Many important microfluid applications require the control and transport of particles immersed in... more Many important microfluid applications require the control and transport of particles immersed in a fluid. We propose a model for automatically planning good trajectories from an arbitrary point to a target in the presence of obstacles. It can be used for the manipulation of particles using actuators of mechanical or electrical type. We present the mathematical formulation of the model and a numerical method based on the optimization of travel time through the Bellman's principle. The implementation is focused on square grids such as those built from pixelated images. Numerical simulations show that the trajectory tree produced by the algorithm successfully avoids obstacles and stagnant regions of the fluid domain.

Mathematics and Computers in Simulation

The Multiscale Robin Coupled Method (MRCM) is a recent multiscale numerical method based on a non... more The Multiscale Robin Coupled Method (MRCM) is a recent multiscale numerical method based on a non-overlapping domain decomposition procedure. One of its hallmarks is that the MRCM allows for the independent definition of interface spaces for pressure and flux over the skeleton of the decomposition. The accuracy of the MRCM depends on the choice of these interface spaces, as well as on an algorithmic parameter β in the Robin interface conditions imposed at the subdomain boundaries. This work presents an extensive numerical assessment of the MRCM in both of these aspects. Two types of interface spaces are implemented: usual piecewise polynomial spaces and informed spaces, the latter obtained from sets of snapshots by dimensionality reduction. Different distributions of the unknowns between pressure and flux are explored. Two non-dimensionalizations of β are tested. The assessment is conducted on realistic, high contrast, channelized permeability fields from a SPE benchmark database. The results show that β, suitably non-dimensionalized, can be fixed to unity to avoid any indeterminacy in the method. Further, with both types of spaces it is observed that a balanced distribution of the interface unknowns between pressure and flux renders the MRCM quite attractive both in accuracy and in computational cost, competitive with other multiscale methods from the literature c

The derivation of an a posteriori error estimator for frictionless contact problems under the hyp... more The derivation of an a posteriori error estimator for frictionless contact problems under the hypotheses of linear elastic behavior and infinitesimal deformation is presented. The approximated solution of this problem is obtained by using the Finite Element Method. A Penalization or Augmented-Lagrangian technique is used to deal with the unilateral boundary condition over the contact boundary. An a posteriori error estimator suitable for adaptive mesh refinement in this problem is proposed, together with its mathematical justification. Up to the present time, this mathematical proof is restricted to the Penalization approach. Several numerical results are reported in order to corroborate the applicability of this estimator and to compare it with other a posteriori error estimators.

In this paper, we present numerical simulations of saline, discontinuous density currents, in two... more In this paper, we present numerical simulations of saline, discontinuous density currents, in two and three dimensions. The simulation of these flows poses a severe challenge for all codes. In fact, the currents present characteristic flow instabilities at the interface which are constituted by small spatial scales. A very fine resolution of these scales is needed to adequately capture the instabilities. The two-dimensional simulations reported herein were performed with two CFD codes. The first one is a comprehensive finite-element platform, whereas the other one is a commercial code. The runs were undertaken under quite similar conditions. Simulations show that only when the mesh employed in the commercial code is strongly refined a convergent solution is attained, which is similar to the solution obtained with the finite-element CFD code. This result would warn about the indiscriminate use of commercial codes with supposedly "fine" meshes when simulating complex underflows. The solution with the finite-element code, in turn, shows the shedding of large vortices containing salt. These vortices do not have a physical basis, but they correspond to the true solution of the twodimensional Navier-Stokes Equations.

An analysis of the two-%uid model in the case of vertical fullydeveloped laminar bubbly%ows is co... more An analysis of the two-%uid model in the case of vertical fullydeveloped laminar bubbly%ows is conducted. Firstlythe phase distribution in the central region of the pipe (where wall e4ects vanish) is considered. From the model equations an intrinsic length scale L is deduced such that the scaled system reduces to a single equation without parameters. With the aid of this

Numerical Heat Transfer Part a Applications, Apr 1, 2003

... 9. GC Buscaglia, EA Dari, JE Martın, DL Arnica, and FJ Bonetto, Finite Element Modeling of Li... more ... 9. GC Buscaglia, EA Dari, JE Martın, DL Arnica, and FJ Bonetto, Finite Element Modeling of Liquid Deuterium Flow and Heat ... G. Buscaglia, F. Basombrıo, and R. Codina, Fourier Analysis of an Equal-Order Incompressible Flow Solver Stabilized by Pressure-Gradient Projection ...

The possibility of improving the performance of lubricated surfaces through surface texturing has... more The possibility of improving the performance of lubricated surfaces through surface texturing has been a topic of intense research in the latest years. Considerable efforts in both experimental and numerical works have been made to study the effects of micro-textures in load capacity, friction and wear. In the industry it has been known for a long time that some texturing is required in the liners of combustion engines to avoid stiction with the piston rings. The numerical simulation of that problem poses a challenge in modeling the intervening phenomena (cavitation, starvation, ring dynamics) and solving it efficiently. In this work we present numerical simulations of the piston ring/liner problem in the hydrodynamic lubrication regime using the Elrod-Adams model and a mass-conserving algorithm. Realistic values are assumed for the parameters defining the problem. The formation of cavitation bubbles and its relation with the load-carrying capacity, friction and clearance is analyzed by considering different texture configurations and shapes in one-dimensional tests. Afterwards, two-dimensional dimpled surfaces are simulated for more than a hundred different texture configurations in the hydrodynamic lubrication regime for several Stribeck numbers. A robust code accelerated by means of a multigrid implementation allowed the realization of this extensive study. Results show that friction and wear reduction are attainable by virtue of dimples of the size of the contact, although the gain decreases or disappears as the mixed lubrication regime is approached.

Revista Internacional De Metodos Numericos Para Calculo Y Diseno En Ingenieria, 1992

En este trabajo se estudia el fenómeno de migración de hidrógeno y formación de blisters de hidru... more En este trabajo se estudia el fenómeno de migración de hidrógeno y formación de blisters de hidruro ante el contacto entre tubos de presión y tubos calandria en reactores tipo CANDU. Este fenómeno es actualmente admitido como uno de los principales factores limitantes de la vida Útil de este tipo de reactores, desde que ocasionara el incidente de Pickering en 1983. Se desarrolla un método numérico basado en la regularización de las ecuaciones constitutivas que, con el tratamiento usual de elementos finitos y con un esquema de Newton-Raphson, permite resolver el citado problema sobre redes generales. Se incluyen resultados unidimensionales y bidimensionales, que muestran buen acuerdo con soluciones cuasi-analíticas disponibles (caso l-D) e ilustran la capacidad del método empleado.

Tribology International, 2016

Models of the friction force are assessed by direct comparison with two-dimensional Navier-Stokes... more Models of the friction force are assessed by direct comparison with two-dimensional Navier-Stokes results. A three-term formula obtained from asymptotic expansion provides a reasonable estimate of the hydrodynamic friction of rough runners even at sub-micron clearances. Simulations of a measured honed surface are then reported using the conservative time-dependent Elrod-Adams model with spatial resolutions as fine as 0.25 μm per cell (4000 Â 800 mesh). Mesh convergence of the numerical method is observed. Cell sizes between 0.5 μm and 1 μm appear as a reasonable compromise of accuracy and cost for the simulation of honed runners. The significance of each term of the friction formula is discussed, so as to assess the error involved in neglecting terms of the friction formula.

Resumen. Una de las dificultades prácticas de la simulación de sistemas termohidráulicos, es la p... more Resumen. Una de las dificultades prácticas de la simulación de sistemas termohidráulicos, es la presencia de varios subsistemas de características geométricas muy diferentes. Algunos, como tuberías o intercambiadores de calor simples, se hallan muy bien caracterizados por modelos simples (ODE's) y no requieren de herramientas CFD para predecir su comportamiento dinámico. Otros subsistemas, tales como componentes de diseño innovativo, requieren un análisis detallado de flujo; en cuyo caso la simulación vía CFD es efectiva. Por lo tanto es necesario obtener estrategias eficientes de acople entre los modelos matemáticos y numéricos que representan a cada componente, a los fines de predecir el comportamiento dinámico del sistema completo. En este artículo presentamos resultados recientes de nuestro trabajo en esta área, restringiéndonos a descomposiciones del circuito (dominio) sin solapamiento y orientado al desarrollo de algoritmos que permitan el tratamiento de cada componente (o subsistema) como una caja negra. Las simulaciones CFD de los componentes complejos se realizó utilizando el método de elementos finitos estabilizado, donde tanto las tensiones como los caudales han sido calculados de manera variacionalmente consistente. Con base en la teoría clásica de descomposición de dominio, presentaremos los resultados obtenidos mediante un esquema Dirichletto-Neumann, analizando también otras variantes inspiradas en el método de Newton y algunas técnicas de aceleración de convergencia tales como el acelerador de Aitken. Dichos resultados muestran que, para flujos transitorios fuertemente no lineales, la selección de los métodos de acoplamiento entre subsistemas permite mejoras importantes tanto en tiempo de resolución como en precisión de los resultados obtenidos.

Journal of the Brazilian Society of Mechanical Sciences and Engineering

TEMA (São Carlos)

Mathematics and Computers in Simulation

Numerical Heat Transfer Part a Applications, Apr 1, 2003

Revista Internacional De Metodos Numericos Para Calculo Y Diseno En Ingenieria, 1992

Tribology International, 2016