4.10. Variable Equation

A variable element can be used to define a function including several state variables. The equation can be expressed as a function expression or as a subroutine specified by users. Good initial condition helps to converge in the initial assembly process. The value of a variable element can be referenced by VARVAL (equation name). Expressions or User Written Subroutine can be utilized to define this element. Variable equation elements are defined by the Variable Equation command in the Subentity menu.

Figure 4.133 Variable Equation List dialog box

• No: Shows the number of equations.

• Name: Shows the name of equation.

• Expression: Shows the defined equation.

• Comment: Shows the comment of the Variable Equation.

• Create: Creates a Variable Equation.

• Insert: Inserts a Variable Equation at the current cursor row.

• Delete: Deletes a Variable Equation at the current cursor row.

• Create or Insert as shown in Figure 4.133 and specify Name and the type of equation as shown in Figure 4.134.

  

  Figure 4.134 Variable Equation dialog box

  • Name: Specifies the name of variable equation.

  • Type: Choose the type of expression as Standard Variable Equation or User Subroutine Equation.

  • EL: Accesses the Expression List dialog box.

  • PV: Accesses the Parametric Value dialog box.

  • Initial Condition: Specifies the initial condition.

  • Inactive Flag: If you check this option, this variable equation becomes inactive.

  • Note: If this equation is used in the expression of a joint or a force, the error message appears when executing the analysis.

How to use a Variable Equation in an Expression

The user can use a variable in an expression as follows:

VARVAL(equation name)

Figure 4.135 Expression using equation name

The user can also register the variable and refer the variable by the register id as follows:

VARVAL(id)

Figure 4.136 Equation using resister id