Persona: Español Garrigos, José
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Español Garrigos
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Publicación Shear thickening of a non-colloidal suspension with a viscoelastic matrix(Cambridge University Press, 2019) Vázquez Quesada, Adolfo; Español Garrigos, José; Tanner, Roger I.; Ellero, Marco; https://orcid.org/0000-0003-1365-6052; https://orcid.org/0000-0001-8894-0395We study the rheology of a non-colloidal suspension of rigid spherical particles interacting with a viscoelastic matrix. Three-dimensional numerical simulations under shear flow are performed using the smoothed particle hydrodynamics method and compared with experimental data available in the literature using different constant-viscosity elastic Boger fluids. The rheological properties of the Boger matrices are matched in simulation under viscometric flow conditions. Suspension rheology under dilute to semi-concentrated conditions (i.e. up to solid volume fraction ϕ=0.3 ) is explored. It is found that at small Deborah numbers De (based on the macroscopic imposed shear rate), relative suspension viscosities ηr exhibit a plateau at every concentration investigated. By increasing De , shear thickening is observed, which is related to the extensional thickening of the underlying viscoelastic matrix. Under dilute conditions ( ϕ=0.05 ), numerical results for ηr agree quantitatively with experimental data in both the De and ϕ dependences. Even under dilute conditions, simulations of full many-particle systems with no a priori specification of their spatial distribution need to be considered to recover precisely experimental values. By increasing the solid volume fraction towards ϕ=0.3 , despite the fact that the trend is well captured, the agreement remains qualitative with discrepancies arising in the absolute values of ηr obtained from simulations and experiments but also with large deviations existing among different experiments. With regard to the specific mechanism of elastic thickening, the microstructural analysis shows that elastic thickening correlates well with the average viscoelastic dissipation function θelast , requiring a scaling as ⟨θelast⟩∼Deα with α⩾2 to take place. Locally, despite the fact that regions of large polymer stretching (and viscoelastic dissipation) can occur everywhere in the domain, flow regions uniquely responsible for the elastic thickening are well correlated to areas with significant extensional component.Publicación Solution to the plateau problem in the Green-Kubo formula(American Physical Society, 2019-02-19) Torre Rodríguez, Jaime Arturo de la; Duque Zumajo, Diego; Español Garrigos, JoséTransport coefficients appearing in Markovian dynamic equations for coarse-grained variables have microscopic expressions given by Green-Kubo formulas. These formulas may suffer from the well-known plateau problem. The problem arises because the Green-Kubo running integrals decay as the correlation of the coarse-grained variables themselves. The usual solution is to resort to an extreme timescale separation, for which the plateau problem is minor. Within the context of Mori projection operator formulation, we offer an alternative expression for the transport coefficients that is given by a corrected Green-Kubo expression that has no plateau problem by construction. The only assumption is that the Markovian approximation is valid in such a way that transport coefficients can be defined, even in the case that the separation of timescales is not extreme.Publicación Boundary conditions derived from a microscopic theory of hydrodynamics near solids(American Institute of Physics, 2019-04-08) Camargo-Trillos, Diego; Torre Rodríguez, Jaime Arturo de la; Delgado Buscalioni, Rafael; Chejne, Farid; Español Garrigos, JoséThe theory of nonlocal isothermal hydrodynamics near a solid object derived microscopically in the study by Camargo et al. [J. Chem. Phys. 148, 064107 (2018)] is considered under the conditions that the flow fields are of macroscopic character. We show that in the limit of macroscopic flows, a simple pillbox argument implies that the reversible and irreversible forces that the solid exerts on the fluid can be represented in terms of boundary conditions. In this way, boundary conditions are derived from the underlying microscopic dynamics of the fluid-solid system. These boundary conditions are the impenetrability condition and the Navier slip boundary condition. The Green-Kubo transport coefficients associated with the irreversible forces that the solid exert on the fluid appear naturally in the slip length. The microscopic expression for the slip length thus obtained is shown to coincide with the one provided originally by Bocquet and Barrat [Phys. Rev. E 49, 3079 (1994)].Publicación Microscopic Slip Boundary Conditions in Unsteady Fluid Flows(American Physical Society, 2019-12-31) Torre Rodríguez, Jaime Arturo de la; Duque Zumajo, Diego; Camargo-Trillos, Diego; Español Garrigos, JoséAn algebraic tail in the Green-Kubo integral for the solid-fluid friction coefficient hampers its use in the determination of the slip length. A simple theory for discrete nonlocal hydrodynamics near parallel solid walls with extended friction forces is given. We explain the origin of the algebraic tail and give a solution of the plateau problem in the Green-Kubo expressions. We derive the slip boundary condition with a microscopic expression for the slip length and the hydrodynamic wall position, and assess it through simulations of an unsteady plug flow.Publicación Internal dissipation in the Dzhanibekov effect(Elsevier, 0001-08-20) Torre Rodríguez, Jaime Arturo de la; Español Garrigos, JoséThe Dzhanibekov effect is the phenomenon by which triaxial objects like a spinning wing bolt may continuously flip their rotational axis when initially spinning around the intermediate axis of inertia. This effect is closely related to the Tennis Racket theorem that establishes that the intermediate axis of inertia is unstable. Over time, however, dissipation ensures that a torque free spinning body will eventually rotate around its major axis, in a process called precession relaxation, which counteracts the Dzhanibekov effect. Euler’s equations for a rigid body effectively describe the Dzhanibekov effect, but cannot account for the precession relaxation effect. A dissipative generalization of Euler’s equations displays two dissipative mechanisms: orientational diffusion and viscoelasticity. Here we show through numerical simulations of the dissipative Euler’s equations that orientational diffusion, rather than viscoelasticity, primarily drives precession relaxation and effectively suppresses the Dzhanibekov effect.Publicación Enseñanza y divulgación de las Ciencias: el Programa de Doctorado en Ciencias de la UNED(Universidad Nacional de Educación a Distancia (España). Facultad de Ciencias, 2014-01-01) Español Garrigos, José