Learning Forum

[Mingli Yan]

Hi everyone,

I’m using the MHD module to simulate the arc behaviour by ANSYS Fluent. Now, I want to define the electric conductivity of a material, which is a variable dependent on the electrical potential and current density, and I attempt to use UDF and expression to define the conductivity. However, the named expression function seems different to the expression of the material property dialogue, as the expression provided in the material property dialogue does not support such lots of variables in the named expression function. Additionally, I don’t know the location of the UDMs which reserve the current density and electrical potential, so I neither can’t use UDF to define the conductivity.

Could you please let me know the method to check the location of the UDMs used by MHD module so I can call them in the UDF to define the conductivity via the macro like C_UDM? Or if the named expression can be used to define the property, it should be easier.

Thanks!

[Murari Iyengar]

Hi, you can refer 2.3. Model-Specific DEFINE Macros (ansys.com) for UDF macros. You can also refere Appendix B. DEFINE Macro Definitions (ansys.com) for additional macros. You can create it using Named Expressions also. To do this, you can create multiple NE, one for every variable and a last one for conductivity which is dependant on these variables. 

[Mingli Yan]

 

Thanks a lot for your reply!

However, there is still a problem about how to use NE to define the conductivity. The dialogues of NE and the expression called from property dialogue are shown below. Maybe you can see that the variables available in NE are different to the expression used to define the property. Once I enter some variables in NE that are not supported by the expression in the property dialogue, the NE won’t show in the expression in the property dialogue. Is that because the units of the variables are not defined? If that is true, could you please give me some instructions on how to define the unit of these variables to make them available to define the properties?