FMU unit error for models containing valves

[ohly87]

Describe the bug
When exporting models containing valves from Dymola 2025 to fmu, they cannot be run with FMPy 0.3.27 because the unit of the flow coefficient (m(1/2).kg(1/2)) is missing in the modelDescription.xml.

To Reproduce
Steps to reproduce the behavior:

1. Open model 'Buildings.Fluid.Actuators.Valves.Examples.TwoWayValves'
2. Export FMU (tried 2.0 and 3.0)
3. Run python script:
   from fmpy import simulate_fmu
   simulate_fmu('TwoWayValves.fmu')
4. See the error:
   ValidationError: Failed to validate modelDescription.xml:
   • The unit "m(1/2).kg(1/2)" of variable "valLin.Kv_SI" (line 667) is not defined.
     [...]

Expected behavior
No error should occur. The missing unit can manually be added in the modelDescription.xml to avert the error :
<Unit
name="m(1/2).kg(1/2)"/>

Version

• Modelica Buildings Library: 12.1.0
• Modelica simulation environment: Dymola 2025x Refresh 1
• FMPy 0.3.27
• Windows 11

[jelgerjansen]

@ohly87 thanks for reporting this. As this refers to a model from the IBPSA library, I added a new issue there to discuss and fix this issue: ibpsa/modelica-ibpsa#2074