4.5.4. User Functions

User functions are 1D tables specified directly in the input file (at the Sierra scope) that can be used wherever generic expressions are available in Aria (e.g. material properties, boundary conditions, initial conditions, sources). These functions can be either piecewise linear (most common) or piecewise constant (step functions).

A user function is defined at the Sierra-level in the input file. Examples of piecewise linear and piecewise constant functions are shown below. Evaluations outside the table bounds are clipped to the table boundary, not extrapolated.

Begin Sierra Aria

  # ...

  Begin Definition for Function spec_heat_ss304
    Type is Piecewise Linear
    Begin Values
      293.0  500
      433.0  800
    End Values
  End

Begin Sierra Aria

  # ...

  Begin Definition for Function heat_flux
    Type is Piecewise Constant
    Begin Values
      0.0  0
      1.0  500
    End Values
  End

These functions can be used for material properties using the user_function model:

specific heat = user_function name = spec_heat_ss304 X = temperature

or in boundary conditions or other places with a similar syntax:

BC Flux for energy on surface_1 = user_function name = heat_flux X = time

The full set of syntax options for user functions can be found in the User Functions command reference section, which includes additional commands for scaling and offset options for both data columns and several less commonly used options.