At the project level, you can create custom parameters that are not directly associated to a data model property. They can be custom input or custom output parameters that can be defined by a constant value (e.g., "12.5 [cm]" or "sin(pi/2)"), or they can be derived parameters, defined by an expression of other parameters (e.g., "P2+3*P3").

To create a derived parameter, enter the expression statement in the Expression field of the Properties of Outline view or in the Value field of the Outline of Parameters view. Both derived parameters and constant values can be added in the Outline of Parameters view, but once added, derived parameters become read-only in the Outline view. You must use the Properties of Outline view to edit them. Constant values, however, can be edited in the Outline of Parameters view.

If the expression defining the custom parameter results in a quantity, it will infer its quantity name from the value produced by the expression evaluation. As a consequence, if the expression is a sum of multiple terms, every term needs to be made of the same quantity. For example, if the resulting quantity is 3.4[m^2], the new custom parameter will take on the quantity name “Area.” In some cases, more than one quantity name may be valid for the expression. In these cases, the parameter quantity name will not be set, but can be selected from a list in the parameter Properties view. Once the value quantity name (e.g., Area) is determined from the unit of the value, it can only be subsequently changed by changing the parameter's "value quantity name" property setting. You cannot change the expression (e.g., from area to volume) without changing the value quantity name.

The expression defined for a custom boolean parameter can be the Python values True or False, or a Python logical expression, such as “P1 > P2” or “P1 == 10 and P2 == 10”. For a parameterized boolean parameter, you can select True/False from the dropdown in the Value column.

The expression defined for a custom string parameter must be quoted with single or double quotes, i.e., ‘string value’ or “string value”.

You can chain output to input parameters to allow an input to be driven directly from the current value of an output, provided that the chaining does not create a circular dependency. To chain parameters, change the input parameter definition to an expression involving other parameters. To create a derived variable, first insert an expression and then edit the Expression field in the Properties of Outline view.

The ANSYS Workbench expression parser supports standard math functions and operators, as well as units for quantities. Dimensional quantities are defined in units which are a combination of one or more separate units.

ANSYS Workbench expression and mathematical function evaluation is based on the Python 2.6 programming language (www.python.org) and inherits some behavior as described here. All Python numeric and function capabilities can be used. For example, Python provides support for octal (base 8) and hexadecimal (base 16) numbers. To tell Python that a number should be treated as an octal numeric literal, simply append a zero to the front. Appending a zero and an x to the front of a number tells Python to treat the number as a hexadecimal numeric literal.

Do not start expressions with an “=” operator. To define a derived parameter P5 such that P5=P2+3*P3, set the expression to P2+3*P3, given that P2 and P3 are existing parameters.

Expressions that involve quantities must be dimensionally consistent. The + and - operators require that the two operands have compatible units. For example, you cannot add an Area parameter to a Length parameter; both units must be Length or both units must be Area. The * and / operators do not have this limitation. They allow one operand to be a quantity with a unit and the other operand to be a dimensionless factor. Or, they allow both operands to be quantities with units where the result is a different quantity type. For example, Length/Time results in a quantity with a Velocity unit.

Expressions support a number of intrinsic functions, outlined below. These functions support both standard numeric values and quantities as arguments.

The arguments for trigonometric functions are evaluated as follows:

You can include units, assuming the unit makes sense in context of the expression. For example, P2+3[mm]*P3 is valid if mm is a valid unit expression for P2 and P3 (e.g., if P2 is torque and P3 is force, or if P2 is area and P3 is length).

The project unit system is used to evaluate the expressions. For temperatures, absolute temperature values are used in expression evaluation. All quantity values in an expression are converted to the project unit system.

The general units syntax in ANSYS Workbench is defined as [multiplier|unit|^power], where multiplier is a multiplying quantity or its abbreviation (e.g., mega (M), pico (p), etc.), unit is the unit string or abbreviation (e.g., gram (g), pound (lb) foot (ft), meter (m), etc.), and power is the power to which the unit is raised. See Table 1: Unit Multipliers and Table 2: Example Quantities and Units for examples of multipliers and commonly used units.

When typing units in an expression, the units must be enclosed by square braces [...]. You will usually not see the braces when selecting units from a list of commonly used units. In general, units declarations must obey the following rules:

Once the value quantity name (e.g., Area) is determined from the unit of the value, it can only be subsequently changed by changing the parameter's "value quantity name" property setting. You cannot change the expression (e.g., from area to volume) without changing the value quantity name. Automatic unit conversion is only done when the quantity name is known.