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Re: [lammps-users] Errors in lubricate/poly ?
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Re: [lammps-users] Errors in lubricate/poly ?

From: Steve Plimpton <sjplimp@...24...>
Date: Wed, 21 Jun 2017 08:22:43 -0600

I'm CCing Dan Bolintineanu and Dave Heine who can likely
answer these Qs.


On Wed, Jun 21, 2017 at 4:54 AM, Ranga Radhakrishnan <r.radhakrishnan@...652...> wrote:

I think that I have a few issues with the lubricate/poly implementation in LAMMPS based on my reading of Microhydrodynamics book by Kim and Karilla [1].

1) The gap-distance (h_sep) between the particles should be scaled by (radi+radj)/2 and not as radi, where radi, radj are the radii of the two particles.

2) The first term in the squeeze force seems to be missing a prefactor of 2.

3) \omega^\infty seems to have the wrong units. It is because "h_rate" has the units of length.

4) The pump term is also incorrect for particles of different sizes. Briefly, specific cases of calculation of torques in Ref. [1] cannot be used to write down a generalized version.

Please look at the attached pdf for a more detailed explanation on why I raised these concerns, and how to implement a "corrected" lubrication force if you agree with my concerns. Just to be clear, I have looked at previous messages in the mailing list before I send this message, and I don't think any of the previous messages have answered my concerns.



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