Using expressions to define boundary conditions

There are two categories of boundary conditions with regard to expressions:

• Boundary conditions where you specify the magnitude and spatial distribution with a single expression.

• Boundary conditions where you specify the magnitude with an expression and specify the spatial distribution with a field.

Specifying magnitude and spatial distribution in a single expression

The expression can have either a spatial independent domain or an independent domain that is a combination of spatial variables and one non-spatial variable. The valid non-spatial variables are time, frequency, and temperature.

Examples of boundary conditions for which you can specify the magnitude and spatial distribution with a single expression include Pressure and Enforced Displacement Constraint. Depending on your selection in the Type group of the boundary condition dialog box, you specify these expressions in either the Magnitude or Components group of the dialog box.

Specifying magnitude with an expression and spatial distribution with a field

You use an expression with a non-spatial independent domain of time, frequency, and temperature to specify the magnitude, and a field with a spatial independent domain to specify the spatial distribution.

Examples of this type of boundary condition include Force and Moment. You specify the expression that represents the magnitude of the boundary condition in the Magnitude group of the dialog box. You specify the field that represents the spatial distribution of the boundary condition in the Distribution Field group of the dialog box.

Because you use an expression to specify magnitude and a field to specify spatial distribution, the software scales the product of the expression and field so that the cumulative magnitude of the distributed boundary condition at a given time, frequency, or temperature is equal to the value of the expression at the same time, frequency, or temperature.

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