About inlet velocity UDF and divergence problems

Hi everyone,

I met two problems when I studied a tutorial “Pulsating fluidized bed (TFM): Impose fluctuating inlet velocity”.

I had downloaded and read the PDF file from this link 3.11. Advanced Tutorials — MFiX 21.3 documentation, before I began to set through the GUI. Fortunately, the 2D two fluid method (TFM) case ran well. However, when changed it to a 3D DEM one, the solver showed an error message below.


(1) I am not sure how to deal with this issue. Is it caused by the change of dimension (from 2D to 3D) or solver (from TFM to DEM). Do I need to revise the code files? Which lines in code files are wrong?

(2) Which lines in the code files mean the assignment of gas velocity components u_g, v_g and w_g? For example, the gas velocity has three components. How can I confirm that the values in data_kf_0001.txt have been assigned to the y component of the gas velocity? Is the velocity assignment part only in usr1.f (in the zip file below).

My case is attached here in a zip file. Pulsating_fluid_bed_2D_DEM.zip (9.4 KB)

Thank you.

Hi Fei. Are you sure you attached the right files? When I run this case I get 8 errors, but none related to READ_KF.

These are the errors I see:

Error from check_data/check_solids_dem.f:438
Required input not specified: MEW

Error from check_data/check_solids_dem.f:446
Required input not specified: MEW_W

Error from check_data/check_solids_dem.f:458
Illegal or unknown input: MEW_R = 0.0000

Error from check_data/check_solids_dem.f:466
Illegal or unknown input: MEW_RW = 0.0000

Error from check_data/check_solids_dem.f:547
Required input not specified: KN

Error from check_data/check_solids_dem.f:565
Required input not specified: KN_W

Error from check_data/check_solids_dem.f:641
Required input not specified: DES_EN_INPUT(1)

Error from check_data/check_solids_dem.f:683
Required input not specified: DES_EN_WALL_INPUT(1)

Can you ensure you uploaded the correct file? Also please let me know what platform (Windows/Linux/etc) you are running on. Thanks!

Did you build a custom solver for this case? READ_KF is not a standard MFiX key, it is defined in usr_init_namelist.f for this case, so if you don’t build the custom solver you will get the READ_KF unknown keyword error.

Hi @cgw

I am sorry I did not describe my question clearly. I ran this case on Window 10 without SMP. I have checked my case and I am sure that I uploaded a right case. I re-debug the case and find the same problem as I described above, if I do not build the solver.

Then, after the solver with SMP on is built, eigth errors as you extracted appear.

I also have done a test without SMP on Windows 10 now by deleting the inlet UDF and the corresponding .f files and find the following two errors:

Error from check_data\check_solids_dem.f:641
Required input not specified: DES_EN_INPUT(1)

Error from check_data\check_solids_dem.f:683
Required input not specified: DES_EN_WALL_INPUT(1)

This means the problem may not lie in the inlet UDF. For this reason, I open a MFIX file for a DEM case, tutorial 3.3. Two Dimensional Fluid Bed, Discrete Element Model (DEM) — MFiX 21.3 documentation, which I ran successfully several days ago. Then, I transfer the related UDF files for tutorial “Pulsating fluidized bed (TFM): Impose fluctuating inlet velocity” to the folder of case 3.3. Here, it run successfully.

Pulsating_fluid_bed_3D_DEM_1.zip (237.7 KB)

Interestingly, when I changed the original TFM case to the DEM one, it reported two errors even if without the consideration of inlet UDF. I am not sure what is wrong.

error.mfx (13.9 KB)

Hoping that more commonly used UDF cases could be accessible, such as defining physical parameters, interficial forces and mass transfer.

Thank you.

When you go from TFM to DEM, you need to make sure you define the DEM parameters. These were not needed and not defined for the TFM run. The error message tells you you need to define the missing parameters. They are in the Solids> DEM pane.

Thank you @jeff.dietiker

I found the blank space and added friction coefficient and nornal spring constant.

However, I am not aware of the missing infornation for restitution coefficients (normal). Luckly, I find the problem under your prompt. Much thanks.

Then, two errors for left and right walls boundary conditions appeared which was beyond expectation. I compared the parameters for the boundary conditions of left and right walls in the boundary conditions pane. I found some of the parameters set in this case were left blank in other DEM cases in which the boundary condition for walls (curved walls) was set.

For this case, the geometry and the domain are rectangular. Hence, I deleted the original wall boundary conditions for the left and right walls and finally the case ran without bug.

Again, thanks.