DT < DT_MIN. Recovery not possible!

[TY1]

Hi,

I am using PIC method to do a simulation and it begins well but after running for about hundreds of steps, it will show the error as ‘DT < DT_MIN. Recovery not possible!’ and the simulation will stop.
ctfb_1_2023-03-19T164442.382008.zip (1003.6 KB)

i could not really locate where causes this error and i have attached the bug report, could you pls have a look at it?Thanks a lot

[jeff.dietiker]

This is a common mistake. Please see items 1-4 from:

Running stl file error

A few things: You should only include the interior wall of the geometry in the STL file. Here you have both sides. You should orient the normal vectors so they point towards the fluid region. Here they point towards the solid region, so you are meshing the wall region, not the fluid region. I like to have the STL geometry stick out from the inlet and outlet planes to get a better mesh along these planes. You should always inspect the geometry/mesh before running the solver. This will most like…

[TY1]

Hello sir,

thanks a lot for your reply. I wonder for all the suggestions you said, can they be set within MFiX? I went through the ‘geometry’ part but couldn’t find any place to set up the things you mentioned.

I am a very new user of this software, so sorry if I am asking some very fundamental questions. Looking forward to your reply

[jeff.dietiker]

You will have to clean the STL file outside the GUI (i.e. with the software you used to generate the STL file). Other steps can be done in the GUI. I would recommend going through this step by step tutorial:

https://mfix.netl.doe.gov/doc/mfix/22.4/html/tutorials/tutorial_cyclone_sms.html

It is likely that the solid inlet pipe will be too narrow to be meshed and will need to be made wider.

[TY1]

Hello sir,

Sorry for disturbing you again. Because i am not sure how to only include the interior wall, I tried to set the wall thickness to zero, i thought this is supposed to work but it didn’t, i still have normal on both sides of the wall , May I ask is this my problem or this way just doesn’t work?

[jeff.dietiker]

This needs to be done in the software (CAD) you used to create the STL file. Right now, you created the geometry by creating an object that represents the walls only. You want to create an object that represents the fluid region. In other words you want to remove all the faces where the vector points outward.

Please take a look at this stl file for an example: 3.21. SMS meshing workflow, cyclone, Discrete Element Model (DEM) — MFiX 22.4 documentation

[TY1]

thank you sir, your advice was really useful~