UDF for moveable surface for Hooper

MFiX How to
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I want to perform a simulation similar to this in Mfix Dem.
For the sliding valve, it should be move after the hopper is filled with packed particles.
If I input some X-velocity at the valve, it starts moving instantly. Whereas, it should move after the particles are packed say at time (t+deltaT).

How should I input the velocity of the internal moveable surface at time (t+deltaT)?

Also I am a beginner in using UDF. Please explain step by step or if there is any tutorial do suggest.

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Can anyone help me out regarding UDF?

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@cgw Hi Charles can you help me out?

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I would suggest two possible approaches:

  1. Run a first simulation with the valve closed, let the particles settle in the hopper. Save the particle configuration at the end of the run:

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    This will create a particle_output.csv file.
    Setup a second simulation with the valve opened. Copy the particle_output.csv from the first simulation to your second simulation directory, and rename it particle_input.csv'. In the SOlids>DEM pane, uncheck "Enable automatic particle generation" so particle_input.csv` is used as initial condition.

  2. Use a keyframe file to move the internal surface STL file. Set the velocity to zero for the first two keyframes (say at time=0 and time=2 s) and then set a non-zero velocity after that to open the valve. You can set the velocity back to zero once the valve is open.