Biomedical subjects

Eirik G Flekkøy

Publications and source records attributed to Eirik G Flekkøy.

6 recordsLinked to original sources

PubMed2005

Flux boundary conditions in particle simulations.

Flux boundary conditions are interesting in a number of contexts ranging from multiscale simulations to simulations of molecular hydrodynamics in nanoscale systems. Here we introduce, analyze, and test a general scheme to impose boundary conditions that simultaneously control the momentum and energy flux into open particle systems The scheme is shown to handle far from equilibrium simulations. It acquires its main characteristics from the requirement that it fulfills the second law of thermodynamics and thus minimizes the entropy production, when it is applied to reversible processes. It is shown both theoretically and through simulations that the scheme emulates the effect of an extended particle system as far as particle number fluctuations, temperature, and density profiles are concerned. The numerical scheme is further shown to be accurate and stable in both equilibrium and far from equilibrium contexts.

Journal Article↗

PubMed2004

Dynamic roughening and fluctuations of dipolar chains.

Nonmagnetic particles in a carrier ferrofluid acquire an effective dipolar moment when placed in an external magnetic field. This fact leads them to form chains that will roughen due to Brownian motion when the magnetic field is decreased. We study this process through experiments, theory and simulations, three methods that agree on the scaling behavior over 5 orders of magnitude. The rms width goes initially as t(1/2), then as t(1/4) before it saturates. We show how these results complement existing results on polymer chains, and how the chain dynamics may be described by a recent non-Markovian formulation of anomalous diffusion.

Colloids↗

PubMed2004

Interaction model for magnetic holes in a ferrofluid layer.

Nonmagnetic spheres confined in a ferrofluid layer (magnetic holes) present dipolar interactions when an external magnetic field is exerted. The interaction potential of a microsphere pair is derived analytically, with precise care for the boundary conditions along the glass plates confining the system. Considering external fields consisting of a constant normal component and a high frequency rotating in-plane component, this interaction potential is averaged over time to exhibit the average interparticular forces acting when the imposed frequency exceeds the inverse of the viscous relaxation time of the system. The existence of an equilibrium configuration without contact between the particles is demonstrated for a whole range of exciting fields, and the equilibrium separation distance depending on the structure of the external field is established. The stability of the system under out-of-plane buckling is also studied. The dynamics of such a particle pair is simulated and validated by experiments.

Journal Article↗

PubMed2003

Thermodynamically consistent fluid particle model for viscoelastic flows.

A recently proposed viscoelastic dissipative particle dynamics model is put into a thermodynamically consistent form that allows for nonisothermal situations. This model consists of fluid particles that have an additional elastic vector characterizing the state of elongation of the molecules within the fluid particle. Very simple physical mechanisms are proposed for the dynamics of the elastic vector that, with the help of the GENERIC formalism, allows us to derive the full set of dynamic equations for the model. The model is further generalized to include polymer diffusion. The connection of the present model with the CONNFFESSIT approach and the Brownian configuration field approach is discussed.

Computer Simulation↗

PubMed2002

Multiscale dissipative particle dynamics.

We present a simplified kinetic derivation of the multiscale Voronoi-based dissipative particle dynamics (DPD) method. The Voronoi tessellation is used to coarse-grain the molecular level of a fluid, resulting in mesoscopic equations of motion for local mass, momentum and energy. The dissipative particles follow the dynamics of extended objects subject to forces including pressure and stresses. The stresses and heat fluxes are computed through constitutive relations, which lead to fluctuating Navier-Stokes hydrodynamics for the solvent. The present formulation is based on the use of statistical mechanical distribution functions and the connection with the underlying molecular description of the fluid is maintained through the pair-distribution function and the intermolecular potential. The main features of this DPD method are the adaptivity of the dissipative particles to the important length-scales of the problem and the explicit role played by the molecular pair-distribution function.

Biological Transport↗

PubMed2002

Flow paths in wetting unsaturated flow: experiments and simulations.

The flow paths and instabilities of gravity driven infiltration of a wetting fluid into a porous medium are studied. The model experiments and simulations independently represent techniques to study the unsaturated flow in porous media, and they produce a consistent picture of how the paths of fluid transport form and depend on the relative strength of the gravitational force. The experiments, which employ a transparent and quasi-two-dimensional model, reveal that the fluid pathways contain an internal link-blob structure and increase in width with decreasing gravity. The model, which couples the well established invasion percolation model for capillary governed flow with a model that describes the viscous film flow in partially filled pores, corroborates these experimental findings.

Journal Article↗