Yuri Dumaresq Sobral

University of Brasília | UnB · Department of Mathematics

Base roughness plays an important role in the dynamics of granular flows but is still poorly understood due to the difficulty of its quantification. For a bumpy base made of spheres, at least two factors should be considered in order to characterize its geometric roughness, namely, the size ratio of flow to base particles and the packing arrangemen...

In this work, we study the aggregation patterns that we observe in systems composed of two and three magnetic particles interacting magnetically and via solid-solid contact in two-dimensions. We use a discrete element method to take into account solid-solid interactions between pairs of particles. The particles are initially separated and, in the c...

The collapse of granular columns in a viscous fluid is a common model case for submarine geophysical flows. In immersed granular collapses, dense packings result in slow dynamics and short runout distances, while loose packings are associated with fast dynamics and long runout distances. However, the underlying mechanisms of the collapse initiation...

A new algorithm for solving nonhomogeneous asymptotically linear and super-linear problems is proposed. The ground state solution of the problem, which in general is obtained as a mini-max of the associated functional, is obtained as the minimum of the functional constrained to the Pohozaev manifold instead. Examples are given of the use of this me...

In this paper we propose and analyze a fully-mixed finite element method for the steady-state model of fluidized beds. This numerical technique, which arises from the use of a dual-mixed approach in each phase, is motivated by a methodology previously applied to the stationary Navier–Stokes equations and related models. More precisely, we modify th...

Consideramos dois dipolos magnéticos fixos no plano, livres para girar, separados por uma distância r, sujeitos a um campo magnético externo homogêneo aplicado com uma certa orientação. Esse sistema é um sistema dinâmico não-linear e o objetivo deste trabalho é determinar e classificar seus pontos de equilíbrio e as bifurcações sofridas pelo sistem...

Hydrodynamic approaches that treat granular materials as a continuum via the homogenization of discrete flow properties have become viable options for efficient predictions of bulk flow behaviours. However, simplified boundary conditions in computational fluid dynamics are often adopted, which have difficulty in describing the complex stick-slip ph...

In various types of many-particle systems, bidispersity is frequently used to avoid spontaneous ordering in particle configurations. In this study, the relation between bidispersity and disorder degree of particle configurations is investigated. By using magnetic dipole–dipole interaction, magnet particles are dispersed in a two-dimensional cell wi...

In various types of many-particle systems, bidispersity is frequently used to avoid spontaneous ordering in particle configuration. In this study, the relation between bidispersity and disorder degree of particle configuration is investigated. By using magnetic dipole-dipole interaction, magnet particles are dispersed in a two-dimensional cell with...

This paper presents a lattice Boltzmann framework for accurate and efficient simulation of free-surface granular flows. The granular assembly is treated as a viscoplastic fluid, whose apparent viscosity varies locally with the shear rate and pressure according to a regularized \mu(I)-rheology. A single-phase free-surface model is employed to track...

Neste trabalho, estudamos escoamentos de fluidos magnéticos em uma cavidade com parede superior móvel. Propomos uma formulação vorticidade-função de corrente para resolver o escoamento e a equação de evolução da magnetização. As equações que regem o escoamento foram discretizadas utilizando o método de diferenças finitas. Identificamos os principai...

The discrete element method is a technique widely used to simulate multi particle systems, in particular granular materials. For conservative systems, the integration of the equations of motions is often performed via a Verlet-type method of order two.[...]

We studied experimentally and numerically the compaction and subsequent expansion dynamics of a granular bed composed of cylindrical repelling magnets contained in a two-dimensional cell. The particles are firstly compressed vertically with a piston at a given strain rate until a maximum force is reached. The piston is then removed at the same stra...

In this work, we present a theoretical study on the stability of a two-dimensional plane Poiseuille flow of magnetic fluids in the presence of externally applied magnetic fields. The fluids are assumed to be incompressible, and their magnetization is coupled to the flow through a simple phenomenological equation. Dimensionless parameters are define...

Immersed granular collapse is a common model case for the study of transient geophysical flows. This paper examines the effects of column size on granular collapses in water, with an emphasis on the granular flow mobility. Laboratory-scale experiments of underwater granular collapses with three different column sizes are carried out, together with...

Basal effects have important implications for the high mobility and long runout of granular flows such as rock avalanches and landslides. However, fundamental understanding of the basal effect in granular flows remains challenging due to the complex forms of base roughness and the multiscale nature of flow-bed interactions. Here we experimentally i...

Executive Summary This report concerns a forming process in which mash is forced from a spreading manifold into moulds on a rotating drum, transported in the moulds underneath a surface held flush with the drum (the shoe), and ejected from the moulds. The quality of the final product is understood to be related to the shear stresses experienced by...

Executive Summary The production of certain chips involves a forming process in which mash is forced from a spreading manifold into moulds on a rotating drum, transported in the moulds underneath surfaces held flush with the drum (the knife and the shoe), and ejected from the moulds onto a belt. The quality of the resultant chips is understood to b...

A new algorithm for solving non-homogeneous asymptotically linear and superlinear problems is proposed. The ground state solution of the problem, which in general is obtained as a mini-max of the associated functional, is obtained as the minimum of the functional constrained to the Pohozaev manifold instead. Examples are given of the use of this me...

We investigate the crucial role of initial packing density on the collapse of granular column in a viscous fluid by means of a three-dimensional coupled Lattice Boltzmann and Discrete Element Method. The proposed numerical scheme is able to capture the pore pressure effect accurately without relying on any predefined dilation function. Two regimes...

Immersed granular collapses may encounter different flow regimes, such as free-fall (dry), fluid-inertial, and viscous regimes, depending on column geometry, particle size, particle density, fluid viscosity, and many other parameters. Understanding the controlling parameters of these regimes is important for both industrial and geological applicati...

We perform coupled fluid-particle simulations to understand the granular collapse in an ambient fluid (in particular, water) with a wide range of initial aspect ratios. We observe both similar and distinct features in underwater collapses compared to their dry counterparts. As aspect ratio a increases, the normalized runout distance follows a piece...

A systematic study is carried out on a fully resolved fluid-particle model which couples the Lattice Boltzmann Method (LBM) and the Discrete Element Method (DEM) using an immersed moving boundary technique. Similar algorithms have been reported in the past decade, however, the roles of major model parameters are yet to be fully understood. To exami...

Bed forms in natural rivers and man-made channels provide the dominant contribution to overall flow resistance and hence significantly affect sediment transport rate. Many laboratory experiments and field observations have been conducted on bed forms, and it was found that theoretical flat-bed assumptions do not give the correct estimation for the...

Hydro-granular flow is a widespread problem characterized by the complicate fluid-particle interactions. The aim of this study is to investigate the crucial role of initial packing density in the immersed granular column collapse using the coupled lattice Boltzmann method and discrete element method. A dense case and a loose case are compared in te...

We perform coupled fluid-particle modeling to understand the collapse of underwater granular columns in comparison with dry cases, with a variety of initial aspect ratios. Our results show that the submerged collapse leads to a shorter runout and thicker front due to the resistance provided by the ambient fluid. An interesting process of vortex for...

The geometric roughness at boundaries has a profound impact on the dynamics of granular flows. For a bumpy base made of fixed particles, two major factors have been separately studied in the literature, namely, the size and spatial distribution of base particles. A recent work (Jing et al. 2016) has proposed a roughness indicator Ra, which combines...

In this work, we investigate one-dimensional concentration instabilities that occur in fluidized beds. We use the averaged equations of motion for fluidized beds and use closure relations for the stress tensors available in the literature. A linear stability analysis is carried out in order to characterize the frequency, the propagation velocity, a...

Instabilities of immersed slopes and cliffs can lead to catastrophic events that involve a sudden release of huge soil mass. The scaled deposit height and runout distance are found to follow simple power laws when a granular column collapses on a horizontal plane. However, if the granular column is submerged in a fluid, the mobility of the granular...

The basal condition for granular chute flows is assumed rough and non-slip in experimental and numerical studies. In mono-disperse flows, a rough base is usually constructed by gluing/fixing a layer of particles that is similar or identical to the flowing particles. However, the base condition is not so clear in bi-disperse flows, where size segreg...

This work focuses on a theoretical investigation of the shape and equilibrium height of a magnetic liquid–liquid interface formed between two vertical flat plates in response to vertical magnetic fields. The formulation is based on an extension of the so called Young–Laplace equation for an incompressible magnetic fluid forming a two-dimensional fr...

Computational fluid dynamics and discrete element method (CFD–DEM) is extended with the volume of fluid (VOF) method to model free-surface flows. The fluid is described on coarse CFD grids by solving locally averaged Navier–Stokes equations, and particles are modelled individually in DEM. Fluid–particle interactions are achieved by exchanging infor...

This work presents a numerical study of the relative trajectories of two magnetic particles interacting in a dilute suspension. The suspension is composed of magnetic spherical particles of different radius and density immersed in a Newtonian fluid. The particles settle relative to one another under the action of gravity and, when in close proximit...

With the motivation of understanding the formation of bubbles in fluidized beds, we investigate the stability of stratified particulate flows to transverse disturbances, leading to gravitational overturning. We consider a one-fluid model in which particles are responsible for the stratification of the flow but do not slip relative to the fluid and...

We consider the unsteady motion of a sedimenting rigid spherical particle in order to examine the relative strength of the hydrodynamical forces acting on particles in fluid flows. The relative strength of the forces on all stages of the particle motion is a major concern for closing constitutive equations describing the more complex motion of part...

Dans ce travail, nous nous sommes intéressés aux instabilités secondaires et à la formation des bulles dans les lits fluidisés. Ce problème est traité dans le cadre de la mécanique des milieux continus, à partir des équations de bilan de masse et quantité de mouvement pour un système diphasique. Des lois constitutives récemment obtenues à partir de...

Resumen – El principal objetivo de este trabajo es el desarrollo de una metodología de tratamiento estocástico de señales turbulentas originadas de experimentos o de simulaciones numéricas. Se desea evaluar los errores in-herentes a la utilización de la hipótesis de ergodicidad y de la consideración de que el proceso es estadística-mente permanente...

The motion and deformation of a drop composed by oil and magnetic microparticles is characterized by scaling arguments based on the governing equations for the flow of magnetic fluids. The scaling predicts that the drift velocity of a magnetic drop is proportional to the square of the applied magnetic field since viscous forces dominate inertia for...

Finite volume method is adapted to simulate momentum and magnetic coupled equations of a laminar magnetic fluid flow. An evolution equation is used to calculate the fluid magnetization. Pressure-driven flow under steady and oscillatory magnetic field is investigated. The magnetostatic limit of the Maxwell's equations is treated in terms of a Poisso...

The stability of a polarized fluidized bed is examined by theory which considers an approach of hierarchic interaction of concentration waves. A linear hyperbolic partial differential equation for particle concentration disturbances is obtained and is recast as the sum of two wave operators of different orders, which represent two kinds of waves pr...

This work focuses on laminar pipe-flows of a magnetic fluid composed of super-paramagnetic particles. The deviations from the equilibrium magnetization arise due to vorticity effects on the flow. In the regime of small deviations of magnetization, the problem is reduced to a weakly nonlinear ordinary differential equation for the velocity. The resu...

The equations governing the motion of a magnetic fluid are presented. These equations are non-linear and give rise to non-Newtonian effects attributable to the magnetization of the fluid. The equations are made dimensionless and the physical parameters of the coupled hydrodynamic–magnetic problem identified. The study is first applied to describe t...

Pressure-driven flow of a magnetic fluid in cylindrical tubes is investigated using numerical simulations. The simulations are based on a Finite Volume Method adapted for incorporating a magnetization evolution equation. The magnetostatic limit of the Maxwell's equations is treated in terms of a Poisson equation numerically integrated. Suitable bou...

The aim of this work is to investigate the stability of a polarized fluidized bed of magnetic particles against plane wave disturbances of small amplitudes. A continuum model is proposed so that continuity and momentum equations are written in terms of averaged variables. Magnetostatic equations are averaged and an equation governing the disturbanc...

In this work the local equations governing the dynamics of fluidized beds are written in terms of averaged variables and constitutive relations based on physical arguments are proposed. The averaged equations are perturbed with small disturbances from the homogeneous fluidization state, and linearized with respect to the perturbations. A stability...