infinite diffusion

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Bernd
Posts: 1504
Joined: Mon Jun 23, 2008 9:29 pm

infinite diffusion

Post by Bernd » Thu Jul 02, 2009 11:18 am

Hi all,

We introduced a new option "infinite_restricted" to handle infinite diffusion in cases with multiple grains. Before this update, infinite diffusion was automatically solved for each grain but not in between the grains if multiple grains of the corresponding phase were present. This procedure intended to distinguish between touching and non-touching grain, but it has the disadvantage that diffusion between grain is not really infinite. Diffusion rather depends strongly on the actual time step, because infinite diffusion is performed only once per phase-field time step inside each grain, and mixing between the grains is a question of overlapping in the interface region.
Now, the user has the choice whether he/she wants to use "infinite" for mixing composition between all grains of the phase, and "infinite_restrictive" to apply infinite diffusion on each grain individually (and such to respect the neighborships of the grains).

Bernd

Bernd
Posts: 1504
Joined: Mon Jun 23, 2008 9:29 pm

Re: infinite diffusion

Post by Bernd » Fri Jul 07, 2017 6:34 pm

Update:

While the keywords "infinite" and "infinite_restricted" are still accepted, they have been replaced by the more systematic keywords "diagonal i" and "diagonal I". Please note that it is not allowed to use the "i" and "I" characters with "multi" because any infinite flux would short circuit all other possible fluxes.
If one element of a phase is solved using infinite diffusion, it makes much sense to switch off the off-diagonal term for all other elements which use this element's gradient. If element 5 of 7 is defined as infinite, the definition for the other elements should e.g. be

"multi ggggngg"

otherwise, time is lost because there is no gradient present for this term.

Bernd

Bernd
Posts: 1504
Joined: Mon Jun 23, 2008 9:29 pm

Re: infinite diffusion

Post by Bernd » Fri Jul 07, 2017 6:36 pm

Update:

While the keywords "infinite" and "infinite_restricted" are still accepted, they have been replaced by the more systematic keywords "diagonal i" and "diagonal I". Please note that it is not allowed to use the "i" and "I" characters with "multi" because any infinite flux would short circuit all other possible fluxes.
If one element of a phase is solved using infinite diffusion, it makes much sense to switch off the non-diagonal term for all other elements which use this element's gradient. If element 5 of 7 is defined as infinite, the definition for the other elements should e.g. be

"multi ggggngg"

otherwise, time is lost because there is no gradient present for this term.

Bernd

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