Expressions must result in a value that is consistent with the requirements of the data model setting being defined. The evaluated value(s) must match the characteristics of the target value: whether it is a single value or a field, and whether it is immutable or mutable.
- Single Values
When an expression evaluates to a single value, it returns a single value at each point of the calculation — that is, there is one value at each coupling step or iteration in the analysis.
Single values are not dependent on mesh or location.
- Fields
When an expression evaluates to a field, it returns a field of values at a given point in the calculation — that is, at a given point in the calculation, there are values throughout the regions on a coupling interface.
Fields are dependent on mesh and location, so evaluation of the expression may yield different values for each node or element of the mesh at each coupling step or iteration.
Note: It is possible to assign a single value to a field. In this case, each location in the field will be set to this value.
- Immutable Values
An expression that does not reference any variables evaluates to an immutable value.
When an expression evaluates to an immutable value(s), the returned value(s) do not change over the course of the analysis.
The expression is evaluated once and the value(s) remain the same at each coupling step or iteration.
- Mutable Values
An expression that references one or more variables evaluates to a mutable value.
When an expression evaluates to a mutable value(s), the returned value(s) vary over the course of the analysis.
The expression is evaluated multiple times, yielding different values at each coupling step or iteration.
Table 32: Example expression values
| Evaluated Value | Setting(s) | Description |
|---|---|---|
|
Immutable Single Value |
End Time |
An expression defining the End Time value is evaluated once. The value does not change during the analysis. |
|
Mutable Single Value |
Time Step Size |
An expression defining a mutable Time Step Size value may evaluate to 1 [s] at a given coupling step and to 2 [s] at a later step. |
|
Mutable Field |
Value |
An expression defining the source side variable values for a Force transfer will yield different values for each coordinate (for example, force) at different coupling steps or iterations. Note also that the components of a vector field may be accessed as scalar fields – force.x, force.y, and force.z.) |