How to derive particle drag force in a DEM simulation

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1

Hello, developers,
I want to export the drag force of particles in DEM simulation, now I set three scalars des_usr_var (12:14) in drag_gs_des.f, but I found that the exported data are all 0 (the following figure). May I ask how this should be handled?
In fact, I have previously referred to the information to export the drag forces directly, which requires “des_explicitly_coupled = False”. After taht, I can get the particle drag force, but the calculation will always fail to converge soon.
Any possible help would be greatly appreciated!

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image581×1042 149 KB

pulsed_bed_quasi_2d_2024-12-31T235240.307409.zip (723.6 KB)

2

Hello,

So first you want to keep des_explicitly_coupled = True
Then you can go to calc_drag_des.f, there you can find FC(II,:) = FC(II,:) + DRAG_FC(II,:)
We include the drag force to contact force here so you can simply do something like this:

        DES_USR_VAR(II,12) = DRAG_FC(II,1)
        DES_USR_VAR(II,13) = DRAG_FC(II,2)
        DES_USR_VAR(II,14) = DRAG_FC(II,3)

This should save drag force to des_usr_var.

1 Like
3

Thank you very much for your reply! I have re-run the calculations as you gave me advice and it does indeed derive the particle drag force.
However, I’m having some new trouble. As you can see in the picture, only some of the particles have drag (on the correct order of magnitude), and most of the particles show 0. May I ask what could be the reason for this? Attached is my case.
pulsed_bed_quasi_2D_DEM_heat_binary_550_600_0Hz.zip (5.7 MB)

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image993×445 92.7 KB

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image1072×684 145 KB

4

Thanks for your suggestion, it helped me to successfully derive the particle drag force. But only a few of the particles have drag, most of the particles are 0. May I ask what could be the reason for this?

5

I actually have no idea but could be the contour range? Looks like most of values are located between 0~5e-7. So you can adjust the value range to check.

Also, solid time step is much smaller than fluid time step, when set des_explicitly_coupled = True, we do a coupling to cast fluid info to particle at the beginning of fluid time step, then during this fluid time step, we assume fluid is stationary and perform solid iteration until solid time can march fluid time. It is not as accurate as continuum coupling (recompute drag at each solid time step). Maybe this also affects the drag.