Mass inlet start time doesn't work

MFiX
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#1

Hello Developers，

I tried to set the “mass inlet start time” so that the inlet starts blowing after 0.3 seconds. But it doesn’t work, it still starts blowing from the beginning of the simulation. By the way, I set it to “1s” ，it also starts blowing from the very beginning.

The results are attached below and I hope to get your answers.Thanks!

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0001549×621 125 KB

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0011551×614 174 KB

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0021544×619 143 KB

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0031546×622 119 KB

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#2

Please attach your input files.

#3

Is there a file here that you’re talking about? I’m sorry I’m a beginner.
demdemdem_2023-09-06T201313.810270.zip (3.9 MB)

#4

Thank you. I am looking at your simulation now, I will reply as soon as I’ve had a chance to let it run for a while.

#6

(previous incorrect reply deleted)

It turns out that the start and stop time for mass inlets only applies to solid particles, not fluid, so your flow is on from t=0, as you observed, and as can be seen in the above animation, where we are coloring particles and fluid by y-component of velocity.

The bc_mi_start_time keyword and its description are confusing. There is nothing that says it is limited to DEM particles. Maybe we can extend it to the gas phase for 23.3.

Thanks for your patience and sorry for the difficulties!

1 Like
#7

Possibly you could use a UDF to turn on the flow at t=0.3.

Or, probably easier, run the simulation up to a stop time of t=0.3 with the inlet gas velocity (bc_v_g) set to 0, then when it stops, set bc_v_g to the desired value, set the stop time to 3s, then do a resume:

shot-2023-09-07_12-14-09
shot-2023-09-07_12-14-09599×542 45.7 KB

You can also use ‘pause’ to pause the simulation and change the inlet velocity while paused.

#8

You can see an example of UDF with keyframe data to make a transient gas inlet in the pulsating fluidized bed example:

image
image1812×729 144 KB

#9

Thank you very much for your answer! It was very helpful .

#10

OK, I’ll study the case carefully later, thanks!

#11

hi，cgw，

I tried setting bc_mi_start_time to 0, but that reported an error. But when I set it to a non-zero value (0.1 or 1) it works fine and gives me the results I want. Perhaps I could set it to a very small non-zero value, but it must not be 0.

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001802×432 7.64 KB

Anyway, it solved my problem. Thanks a lot.

#12

My suggestion was to turn the inlet velocity to 0, not the start time. The start time can be removed completely.

  1. Disable inlet start time, set inlet velocity to 0, set stop time to 0.3s
  2. Run the simulation until it stops
  3. Set the inlet velocity to 30 and resume the simulation

Alternately:

  1. Disable inlet start time, set inlet velocity to 0, set stop time to 3s
  2. Run the simulation until the particles have settled
  3. Hit “pause”, then set inlet velocity to 0
  4. Un-pause the simulation

It’s important to know that simulations can be modified (to a limited extent) while paused, and that completed simulations can be resumed.