[GeoMechanicsApplication] Possibility of multiple UDSM dll in single simulation

[indigocoral]

Impediment:

Writing on the Fortran side in the calculation with two UMATs (which are the same but just with different names) goes wrong. Probably because of unit=10.

Try with Plaxis UDSM also leads to this error message:

Comment - mcgicjn2 - 19-09-2025
@indigocoral Can we revisit this with our new knowledge ? Maybe I can next week.

1. Plaxis soil models don't work in Kratos (license is needed)
2. We have more than 1 soil model available now

We need to try multiple soil models in same UDSM, and multiple in seperate files. Also possible just to rename a UDSM dll and try using two together as this might help testing it is correct.

Comment - avdg81- 11-02-2026
@indigocoral will try the above combinations of DLL usage and report about the results.

[indigocoral]

(I could not attach a zip file to the draft issue thus I had to convert this to an issue.)
Here is the result of my investigation with the combinations I could think of:

Test case	DLL setup	Result	Notes
a_single_udsm_as_starting_point	MohrCoulomb64.dll for both materials	✅ Works	Baseline
multiple_dll_combination_umat_udsm	MohrCoulomb64.dll + MohrCoulombUMAT.dll	❌ Crash	Fails
multiple_dll_both_udsm	MohrCoulomb64.dll + example64.dll	✅ Succeeds	Results differ vs baseline
multiple_dll_both_umat	MohrCoulombUMAT.dll (multiple materials)	❌ Crash	Fails
same_dll_different_name	MohrCoulomb64.dll + renamed copy MohrCoulomb64_same.dll	✅ Succeeds	Results the same as baseline
same_dll_multiple_soil_models	example64.dll with UDSM_NUMBER=1 and UDSM_NUMBER=2 per material	✅ Succeeds	Results differ vs baseline

Here are also the tested files for reference:

multiple_dll.zip