Pause in calculation

MFiX
#1

Hi everyone,

I find the calculation could not be consecutive and pause appear between two time steps when I use DEM. I am not sure whether this is OK?

Is the time step in run pane uded to calculate the gas phase or the solid phase? If the time step is used for one phase, how about the time step for another phase?

Thank you.

#2

Sorry Fei, this question is not easy to understand.
What are you seeing that indicates a pause? Can you show us log entries or something?

– Charles

#3

Hi Charles,

I run a DEM case in Windows 10. For example, the case I run here is tutorial 3.8 (3.8. SMS meshing workflow, cyclone, Discrete Element Model (DEM) — MFiX 21.3 documentation). The case zip file is attached below.

SMS_cyclone_DEM_1.zip (32.5 MB)

A pause seems to appear between two time steps when the SMP is turned on with 12 threads in my computer.


Vedio with SMP.zip (12.7 MB)

I am not sure what may result in this phenomenon and how to solve it. Is it related to my computer?

My second question is what is the time step in the run pane referred to? I mean it is used to calculate the continuous phase (gas) or particles? If the time step is used for one phase, how about the time step for another phase?

Thank you.

#4

This is not a pause, it just takes longer to go through the DEM loop than it takes for the Fluid loop:

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Here it takes about 3.5 seconds for the DEM loop. There is no intermediate message printed while looping in DEM loop. It will take longer as more particles are injected in the cyclone. You can try with fewer threads and see if you really get a benefit from running in SMP, or if the overhead is too costly for this problem size.

The time step in the run pane controls the fluid time step. The solids time step (DEM) depends on the particle properties and is computed internally. It is displayed at the beginning of the run:

At time =   0.000000E+00 sec., setting DEM solids time step, DTSOLID (sec) =   0.179818E-04```

you can also view it in the message popup: click on the blue text showing the number of messages
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This will open a pop-up. Then you can navigate to see the messages:

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#5

Thank you @jeff.dietiker . Could I know how the solver compute the time needed for DEM looping.