Diff Equations in Inspire Motion

Define a single, first-order, user-defined differential equation that entails a single dynamic state, which is integrated with the rest of the system states.

These equations can be used to add additional states to the mechanical system being modeled.

By default, variables names of entities follow a certain convention. For example, all differential equation entities have a variable name starting with “SolverDiffeq_”. This is the recommended convention to follow when building models since it has many advantages in model editing and model manipulation.

For information on how to add or edit an entity like a differential equation, see Entity Creation.

Differential Equation Properties in Inspire Motion

Descriptions of differential equation properties in the Property Editor.

Property Description
General
Name Name of the entity
Variable Name The variable name, a unique identifier string of the entity
ID A unique identifying integer
Properties
Static hold Turn on this option if the value of the differential equation is not permitted to change during static and quasi-static analysis of the solver.
Implicit If the derivative of the differential equation is implicit, turn on this option.
IC Enter a value for the initial condition of the differential equation.
IC dot Enter a value for the initial condition of the first derivative of the differential equation. This option is used in conjunction with the implicit attribute.
Type Select the type of input format for the differential equation and provide inputs according to the format selected.
  • Constant: Enter a Value (value).
  • Spline:
    1. Select a Spline.
    2. Select an Interpolation method:
      • AKIMA
      • CUBIC
      • LINEAR
      • QUINTIC
    3. Enter a value under Independent variable X. The independent variable should be specified in Templex syntax.
    4. Select a spline:
      1. Next to Spline (fx), click the empty field.
      2. In the microdialog, click .
      3. In the Select Spline dialog, select a spline.
      Note: To use a spline, you first need to define a spline that represents the behavior of the solver differential equation.
  • Spline3D:
    1. Select a Spline3D.
    2. Select an Interpolation method:
      • AKIMA
      • CUBIC
      • LINEAR
      • QUINTIC
    3. Specify an expression for Independent variable X and Independent variable Z.
    4. Select a spline3D:
      1. Next to Spline3D (fx), click the empty field.
      2. In the microdialog, click .
      3. In the Select Spline3D dialog, select a spline.
      Note: To use a spline3D, you first need to define a spline3D that represents the behavior of the solver differential equation.
  • Expression: Enter an expression.
Signal
User-defined

Alternatively, use a subroutine to define the differential equation.

  • For User expr, provide an expression with the USER solver function with parameters being passed to the user subroutine.
  • Turn on Use local file and function name to provide a local file for the subroutine. Otherwise, Inspire Motion will search for the subroutine within its search path.
    1. Specify a Local file where the subroutine code can be accessed by the solver. If this option is not specified, the application will search for a subroutine following its user subroutine loading rules.
      Note: The type of file to be specified will depend on the selected function type. For example, if DLL/SO is selected, you can specify a file with a .dll extension (for Windows) or an .so extension (for Linux).
    2. Select a Function type from the dropdown menu:
      • DLL/SO
      • Python
      • MatLab
      • Compose
    3. Specify the Function name in the subroutine that defines the entity, or accept the default name provided by the application.