24.6.1 Building valid field output expressions

To define a new field output variable by operating on individual existing field output variables, you build an arithmetic expression in the expression text field of the Create Field Output dialog box.

An expression is composed of one or more existing field output variable tags and, optionally, one or more operators, transformations, and scalars. See Overview of operations on field output, Section 24.6.2, for information on supported operators. Expressions are evaluated as Python input; entries containing syntax errors will generate non-specific Python exceptions.

The Create Field Output dialog box lists field output by the variable name and by a unique “tag” created by ABAQUS/CAE. The tag for a given field output variable is composed of the step and frame numbers prepended to the output variable name; for example, s1f1_RF is the reaction force at Step 1, Frame 1. This tag enables you to combine output from different steps and frames in one expression.

Field output variables can consist of different types of data that may not be compatible. The Create Field Output dialog box lists the type of each field output variable as one of three general types: scalar, vector, and tensor. The tensor types are further subdivided into five subtypes that describe the dimensionality of the tensor and the components available. The following rules apply:

The following examples demonstrate valid field output expressions:

Example 1

To create a field output variable by finding the difference in the stress fields for two increments, type:

s1f2_S - s1f1_S
in the expression text field of the Create Field Output dialog box.

s1f2_S and s1f1_S are field output variables representing stress at two different increments of a particular step. The result of this equation is a field output variable representing the difference in the stress fields for the two increments.

Example 2

To create a field output variable by expressing pressure in decibels as a function of acoustic pressure, type:

20.0 * log10(s1f1_POR/Pref)
in the expression text field of the Create Field Output dialog box.

Pref is the reference pressure. The result of this equation is a field output variable representing pressure in decibels as a function of the analysis variable POR.

Example 3

To create a field output variable by transforming a tensor result to a user-specified coordinate system:

  1. Select Transformation from the Function list on the right side of the Create Field Output dialog box.

  2. Select a tensor result from the list of field output variables; for example, s1f10_S.

  3. Select a coordinate system transformation to apply; for example, a fixed coordinate system named CSYS-1.

    The expression

    s1f10_S.getTransformedField(datumCsys=o_CSYS_1)
    appears in the expression text field.

The result of this equation is a field output variable representing the transformation of the stress tensor s1f10_S to the CSYS-1 coordinate system.


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