Solids boundary conditions trouble


Trying to perform a simple ‘variation of pressure drop with independent velocities’ campaign.

I must use the Jackson-Johnson partial slip boundary but I am unable to select it. I’m able to change it by opening the .mfx code, but I’m not allowed/unsure how to add the associated parameters. ‘phip’ for specularity is suggested to be left alone, unless a known number is used, which is my case. Pic related:


For some reason, you can’t modify it in the GUI, but you can modify the keyword ‘BC_JJ_PS’ if you open up the .mfx file in editor. 0 to turn it off, 1 to turn it on. After turning it on, you will be able to modify specularity and restitution coefficients.

Someone had a similar issue to which I responded here:

@onlyjus Don’t know if I’ve found a bug, or a workaround to a feature I don’t understand how to use. Even when I activate pure granular flow, the following still appears, where I am unable to toggle JJ on, but can modify the JJ-type. Only able to do so after changing internally in editor…


figured it out pls ignore.

Had to use one of the non-algebraic formulations for viscous stress meodels under solids TFM settings

We try to enable/disable options depending on model selections to try to make sure model combinations are consistent. It is not always obvious why different widgets are disabled.

If you hover over the fields, tool tips will appear providing more information. Hopefully that helps.

How to enable Jackson-Johnson Partial slip boundary. please let me know.

Please do not ask the same question on multiple threads, and please do not re-activate 3-year old threads to ask a new question.
As Justin pointed out, the options are disabled for a reason.

In this case, the GUI is not doing a great job of explaining why the option is disabled. I had to refer to the MFiX specification:

Most of the solids wall BCs are only needed for TFM solids. PIC does not support ANY of the wall BC specifications. DEM only supports keywords associated with the energy equations.

  • Enable Jackson-Johnson partial slip boundary

    • Disabled for DEM and PIC solids
    • Disabled (0.0) for CARTESIAN_GRID = .TRUE.
    • Disabled (0.0) for KT_TYPE = ‘ALGEBRAIC’
    • Disabled (0.0) for KT_TYPE = ‘GHD’
    • Sets keyword BC_JJ_PS(#)
    • DEFAULT 1.0 when not disabled
    • Unsets keyword BC_Hw_s(#,#) to UNDEFINED
    • Sets keyword BC_Uw_s(#,#) to 0.0
    • Sets keyword BC_Vw_s(#,#) to 0.0
    • Sets keyword BC_Ww_s(#,#) to 0.0
    • Enables wall velocity specification (below)
    • Disables transfer coefficient specification (below)

I didn’t know this fact, sorry for the inconvenience, I thought there was already a question in the thread so I’m asking it here.