1. Click Differential Equation icon and then Differential Equation List dialog box appears as following figure.
Figure 1 Differential Equation List dialog box
•No: Shows the number of equations.
•Name: Shows the name of equation.
•Expression: Shows the defined equation.
•Create: Creates a Differential Equation.
•Insert: Inserts a Differential Equation at the current cursor row.
•Delete: Deletes a Differential Equation at the current cursor row.
2. Click Create or Insert as shown in Figure 2 and specify Name and the equation type as shown in Figure 3.
Figure 2 Differential Equation dialog box
•Name: Specifies the name of differential equation.
•Function Type: Choose the function type of Explicit or Implicit.
•Type: Choose the type of expression as Standard Differential Equation or User Subroutine Equation.
•Initial Condition: Specifies the initial conditions.
•DIF: Specifies the value of the state variable.
•DIF1: Specifies the value of the time derivative of the state variable.
•EL: Accesses the Expression List dialog box.
•PV: Accesses the Parametric Value dialog box.
•Hold to Differential Value during the Static Analysis: If you check this option, this variable equation
•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.
3. To create the expression, click EL.
4. Define the expression in the Expression List dialog box.
5. To specify the initial condition, input the value.
6. Click OK.