Dear Mfix Expert,

I am working on a 3D case TFM and have coupled a UDF that shows a successful build when I build using the debug flag. However, when I run the simulation, it doesn’t start and displays the error message ‘Fatal error reported on one or more processes.’

I am having trouble tracking down the source of the error. I have checked my UDF and even tested it in the Fortran compiler, which gave the expected value. Even when I included a print command in the code, the simulation hangs on. Although I have used this UDF in 2D simulations and it has worked, the same UDF does not solve the problem in 3D simulations.

I am not sure how to track the simulation and solve these types of errors in MFix. The error message ‘DT < DT_MIN. Recovery not possible!’ always shows up, but I don’t understand where the error is coming from. Please help.

Compressible: IJK_P_g remaining undefined.

**Error from time_step.f:198**

**DT < DT_MIN. Recovery is not possible!**

Fatal error reported on one or more processes. The. LOG file

may contain additional information about the failure.

The MFiX process has stopped

The previous MFiX run is resumable.

3dcase_2024-04-08T192021.454034.zip (29.4 MB)

Dear Mfix users,

I am eagerly waiting for your reply please help me, why Mfix doesn’t give source of error, so that we can trace or debug the problem easily, in maximum cases error gives **DT < DT_MIN. Recovery is not possible!**

Then how can i know the source of error.

Dear @jeff.dietiker

could you pls help me to resolve the thermal conductivity problem,

I am simulating TFM and applied usr.properties.f for kg and ks. I tracked the problem and found that the problem is coming to get the value of k_g(IJK) value, when i use K_g(IJK) = (1.0 - (SQRT(1.0 - ep_g(IJK)))) simulation is running but when i used K_g(IJK) = (1.0 - (SQRT(1.0 - ep_g(IJK)))) * (0.0257 / ep_g(IJK)). then the simulation is not starting and an error is comes “DT < DT_MIN. Recovery is not possible!

ep_g(IJK) value comes 1.0 in most of the cell.

SUBROUTINE USR_PROP_Kg(IJK)

! Modules

use fldvar, ONLY: ep_g

use param1, only: zero

use physprop, only: k_g

implicit none

```
! Dummy arguments
INTEGER, INTENT(IN) :: IJK
! Assign the fluid conductivity
! print *, "ep_g(IJK) =", ep_g(IJK)
IF (ep_g(IJK) < 1.0 ) THEN
K_g(IJK) = (1.0 - (SQRT(1.0 - ep_g(IJK)))) * (0.0257 / ep_g(IJK))
ELSE
K_g(IJK) = 0.0257
END IF
RETURN
```

END SUBROUTINE USR_PROP_Kg