UDFs can be used to define the value parameters (material parameters, constants appearing in boundary conditions, and so on), or boundary conditions for velocity, temperature, and pressure as functions of other quantities.
Parameters can be functions of the following quantities:
Fields: quantities that vary from point to point in the domain, such as the velocity, the temperature, or the pressure (PMAT-based functions)
Additional quantities: local compression rate, local shear rate, local stretch rate, local vorticity, Giesekus function, component of the rate-of-deformation tensor along the velocity (PMAT-based functions)
Evolution parameter S (EVOL-based functions)
Boundary conditions can be functions of the following quantities:
Fields: quantities that vary from point to point in the domain, such as the velocity, the temperature, or the pressure (PMAT-based functions)
Evolution parameter S (EVOL-based functions)
Note that UDFs for boundary conditions are called only once per evolution step. If you define a velocity UDF that depends, for example, on temperature, this UDF will be evaluated with the velocity values of the previous step (or 0 for the first step); there is no update of the boundary condition with this UDF during iterations.