Seed density model: determine active nucleants?

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cboe
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Seed density model: determine active nucleants?

Post by cboe » Thu Mar 11, 2021 2:49 pm

Hello all

I run a directional solidification model with an initial grain at the bottom. I simulate one solid phase. Furthermore, I allow an additional nucleation from the liquid phase. For this I use the seed density model with 10 classes and give verbose output for nucleation. :arrow: Now I would like to know how much of each class of nucleants are active.

As far as I know there is no specific nucleation output but a nucleation verbose. The command "nucleation verbose" gives me the following output:

Seed number 4 set at time t = 0.14000E-02 s
-------------------------------------------
in the bulk
Phase: 1 (FCC_L12)
Seed type: 1 (9: 2/2) --> Does the number "9" refer to class "9"? What does the 2/2 mean? 2 nucleants of this class were activated?
Local temperature = 919.70 K
Undercooling = 5.7853 K
Grain number = 5

In order to calculate the number of active nucleants I would have to search through the scr-output and count the occurence of the number in the brakets. Is that correct? Or is there another approach to this :?:

Thanks for clarifying and your help :)

Best
Constantin
---- Constantin

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

Re: Seed density model: determine active nucleants?

Post by Bernd » Fri Mar 12, 2021 2:24 pm

Dear Constantin,

If you have a look at the .log output file, in the part corresponding to the nucleation input section, there is a list of the potential seeds per seed class which has been initialized for the given domain size. I guess this is what you call "active".

During run-time, the output
Seed number 4 set at time t = 0.14000E-02 s
-------------------------------------------
in the bulk
Phase: 1 (FCC_L12)
Seed type: 1 (9: 2/2) --> Does the number "9" refer to class "9"? What does the 2/2 mean? 2 nucleants of this class were activated?
Local temperature = 919.70 K
Undercooling = 5.7853 K
Grain number = 5
means that this nucleation event belongs to class 9, that there are 2 active seeds in this class, and that you are observing the second nucleation event for this class. Btw, this output is not related only to "nucleation_verbose" but should appear always. Instead, "nucleation_verbose" is helpful for finding out why nucleation is not happening: e.g. because of shielding, not checking for nucleation, temperature range restrictions, missing driving force...

Naturally, not all "active" seeds necessarily will be nucleated during the simulation, if the critical undercooling is not reached for all of them, if nucleation is not checked often enough, if there exist shields from other seed types, if some seeds are hidden e.g. behind the primary dendrite, etc.

Sometimes you may even get more nucleation events than active seeds for a given seed class: If a nucleated seed disappears for any reason, it may nucleate again. Furthermore, in case you are using moving_frame and the seed type is "bulk", the potential seed positions are transported downwards, while new potential sites will be created at the top (eventually leading to much more nucleation events than anticipated). In the latter case, the list in the .log file shows only the initial numbers.

Bernd

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