srd viscosity

Hello,

is there a way to calculate the viscosity of SRD suspension (srd
fluid+particles) via fix deform?
I have tried to use the virial stress formula and add contributions
from velocity rotations and collisions with big particles as described
in

The Journal of Chemical Physics 135, 134116 (2011); doi: 10.1063/1.3646307

but the results are not very good. Has anyone tried to do this with lammps?

Best regards,
Dimitry

If you want the viscosity of the mixture, I don’t see
why you need to add extra terms to the Pxy, which
should effectively contain everything about the mixture.
I.e. use a standard NEMD method, like those in
the examples/VISCOSITY dir.

There is also a recent paper with Dan Bolintineanu as
first author (in a new journal, Comp Particle Mechanics I
think was the title) that described various nanooparticle
interactions and methods for measuring diffusion
and viscosity, including in SRD background, and presented
some viscosity results as I recall. I’ve CCd Dan
who can comment further.

Steve

Hello!

Steve, thank you for your response. If I have srd particles in my
system the virial stress Pxy will give me just the streaming part. The
other two components (i.e. from velocity rotations and collisions with
big particles) are not accounted for. So I need to calculate these
terms separately and add them.

In the article you mentioned - Comp. Part. Mech. (2014) 1:321–356 DOI
10.1007/s40571-014-0007-6 - they apply Lees-Edwards only for the FLD,
otherwise they use Muller-Plathe to measure viscosity in SRD
simulations. I have tried MP and it works great and the results are
what I expect, but I cant have shear reversals in my simulations
because they break the colloidal structures I am studying. That's why
I was looking towards fix deform. But I have trouble calculating the
stress tensor in deforming box. I was wondering if maybe someone
solved this problem already.

Dimitry

Sorry for the delay - this email got buried.

I see the issue with MP for aggregations,

I don’t know if streaming SRD viscosity has been looked at.

Steve