Persona:
Español Garrigos, José

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0000-0001-5263-2817
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Español Garrigos
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José
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2019 - 20203
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Autor: Duque Zumajo, Diego ×

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Mostrando 1 - 3 de 3
  • Miniatura
    Publicación
    Non-local viscosity from the Green–Kubo formula
    (American Institute of Physics (AIP), 2020-05-07) Duque Zumajo, Diego; Torre Rodríguez, Jaime Arturo de la; Español Garrigos, José; https://orcid.org/0000-0001-7055-5835; https://orcid.org/0000-0002-1657-0820
    We study through MD simulations the correlation matrix of the discrete transverse momentum density field in real space for an unconfined Lennard-Jones fluid at equilibrium. Mori theory predicts this correlation under the Markovian approximation from the knowledge of the non-local shear viscosity matrix, which is given in terms of a Green–Kubo formula. However, the running Green–Kubo integral for the non-local shear viscosity does not have a plateau. By using a recently proposed correction for the Green–Kubo formula that eliminates the plateau problem [Español et al., Phys. Rev. E 99, 022126 (2019)], we unambiguously obtain the actual non-local shear viscosity. The resulting Markovian equation, being local in time, is not valid for very short times. We observe that the Markovian equation with non-local viscosity gives excellent predictions for the correlation matrix from a time at which the correlation is around 80% of its initial value. A local in space approximation for the viscosity gives accurate results only after the correlation has decayed to 40% of its initial value.
  • Miniatura
    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, José
    Transport 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.
  • Miniatura
    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, José
    An 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.