Coupled Navier-Stokes/molecular dynamics simulations in nonperiodic domains based on particle forcing

Steijl, R. and Barakos, G. (2012) Coupled Navier-Stokes/molecular dynamics simulations in nonperiodic domains based on particle forcing. International Journal for Numerical Methods in Fluids, 69(8), pp. 1326-1349. (doi: 10.1002/fld.2641)

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This paper focuses on coupling methods for hybrid Navier–Stokes/molecular dynamics (MD) simulations. The computational domain is split in a continuum flow region, where a finite-volume discretisation of the Navier–Stokes equations is used, and one or more particle domains, where molecular level modelling of the flow is employed. The domains are defined with a partial overlap, in which the flow states are coupled through an exchange of the velocity components. For the steady flows considered, an under-relaxed Newton iteration method is used to drive the coupled system to convergence. The main focus of the present work is on methods to impose nonperiodic boundary conditions on the particle domain(s). A particle forcing is applied in the direction normal to the particle domain boundary to impose the boundary normal velocity component. A novel aspect of the present work is the extension of this method to more general nonplanar particle domain boundaries. The main contribution of the paper is the development of a particle forcing method in the direction tangential to the domain boundary, which is based on the equivalent continuum-flow boundary shear stresses along with an iterative forcing strength adjustment based on the extrapolated particle boundary velocity. Furthermore, an adaptation scheme is presented, which uses the finite-volume flux residuals of the particle bin averaged velocity field as a truncation criterion for the iterative force-update scheme. It is demonstrated that by comparing the residual reduction for the momentum equation in the nonhomogeneous directions during the molecular dynamics simulations with that for a homogeneous direction, the forcing iteration at which the statistical noise in the velocity field dominates the uncertainty in the forcing strength can be determined. At this point the iteration can be truncated. It is shown that with adaptive schemes of this type, the total number of MD evaluations required in a coupled Navier–Stokes/MD simulation can be reduced relative to a hybrid scheme with a fixed number of forcing-strength updates

Item Type:Articles
Glasgow Author(s) Enlighten ID:Barakos, Professor George and Steijl, Dr Rene
Authors: Steijl, R., and Barakos, G.
College/School:College of Science and Engineering > School of Engineering > Autonomous Systems and Connectivity
Journal Name:International Journal for Numerical Methods in Fluids
ISSN (Online):1097-0363

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