Multibody Radiation

[Saint]

Hi,

This is somehow connected to the other post that I sent; I hope that I am not spamming, since the topic was specialized to radiation, I thought it people might benefit people who are learning or might have the similar questions, if separate these two posts/questions.

link to my past question: https://www.elmerfem.org/forum/viewtopic.php?t=8370

The Mesh is almost the same, except that I have removed one of the bodies (Air); consequently, the related equations (NS and KE), material, bodywise condition (boussinesque) have been removed.

I must be missing an important step in setting up the simulation, especially when it comes to radiation. I know my questions might seem elementary or they might already have been answered, but my mind and confidence are not at their best, I really appreciate any help and guidance you might spare.

You can find Mesh, Sif and Solver Log (filled with tones of warnings and errors) in here:
Mesh ~3 Mb : https://drive.google.com/file/d/1UfDLtf ... sp=sharing

case.sif

Sif

(3.06 KiB) Downloaded 13 times

al_rad Solver Log.txt

Solver Log

(153.24 KiB) Downloaded 10 times

[raback]

Hi

Radition surfaces need to know the direction of the normal. Imagine a ball. It is very different case to study the internal and external radiation. Now how Elmer usually defines the normal is by assuming that normal points out of the material for which "emissivity" is given. Most of the time this is good heuristics. Now you seem to have defined the property for both parents which makes the normal ambiguous. There is also a keyword "normal target body" but just removing "emissivity" from air might suffice. Only solids typically have emissivity defined.

-Peter

[Saint]

thank yoou Peter for checking out my post.

the "Air" body that you see in the sif, is a mistake; after I selected the new geometry for this similation (the geometry without air body), elmer has assgined name of "air" to the "wall", and I missed/forgot to rename it back to "wall".

in this simulation there is no Air, and either in my main simulation or in here, there are no body with 0 emissivity.
(even in my main simulation where I have air, its emissivity is not given the software and the field is empty instead of 0).

maybe this image can help:

[raback]

Hi

Namings aside, the code complains as follows:

Code: Select all

ViewFactors: Bodies:  1  3 BC:  1 Ind:  174
WARNING:: ViewFactors: Emissivity defined on both sides!

So boundary element 174 has two parents belonging to bodies 1 and 3. If you only would define the internal boundaries there should never be two parents. So I would double checks which BCs are really defined to participate in radiation.

-Peter