Use the Forces tool to create forces and to edit the orientation and properties of forces.

Create Forces

A force entity, as the name suggests, is used to apply a force and/or a torque on a body.

  1. From the Model Browser, select the system to which the Force entity is to be added.
  2. Right-click on a system in the Model Browser and select Add > Force Entity > Force from the context menu.
    Right-click on a force folder in the Model Browser and select Add Force from the context menu.
    From the Model ribbon, click the Forces icon.
    The Add Force or ForcePair dialog is displayed.
  3. Specify a label and variable name.
    By default, variables names of entities in MotionView follow a certain convention. For example, all force entities have a variable name starting with “frc_”. This is the recommended convention to follow when building models in MotionView since it has many advantages in model editing and model manipulation.
  4. Select whether to create a single force or a force pair.
    A force entity, like most of the entities that are created in MotionView, can be a single entity or a pair entity. Pair entities help in creating models which have symmetric properties.
  5. Click OK to close the window or Apply to continue creating entities.
    Once a force entity has been added to the model, the panel for the force will automatically be displayed in the panel area.

Edit Forces

The created force can be of the type action only or action reaction. An action only force acts on a single body on which force is applied. An action reaction force acts on two bodies, one is called the action body and the other the reaction body.

Define the Connectivity of Forces

A force in MotionView can be defined as Translational, Rotational (torque), TransRotational (combination of force and torque), Line of Action Translational, Scalar along the Z axis, Scalar about the Z axis, or Single Component Rotational type. These properties can be assigned to the force using appropriate tabs that appear based on the selections in the Connectivity tab.

  1. If the Forces panel is not currently displayed, select the desired force by clicking on it in the Model Browser or in the modeling window.
    The Forces panel is automatically displayed.
  2. Select a force type from the Force drop-down menu.
    Note: If the selected graphic is a pair entity, first distinguish between the Left and Right tabs in the panel, and then edit the properties. When defining a pair graphic, use pair entities for Body, Origin, etc.
  3. Select how to define the force from the options in the Properties drop-down menu.
    Depending on your selection, different tabs and collectors will become available.
  4. Define the force using the various Body, Point, and Ref Marker collectors that are needed. Click on a collector and make your selection in the modeling window, or double-click the collector to open the Model Tree (from which the desired entity can be selected).
    • For a force type of Action reaction with a Single Component Rotational property, the rotational axis of torque can be defined using either a point or vector. Click the drop-down arrow next to the Point collector to change your selection.
    • To add a force using explicit markers, click Use explicit markers and specify the marker and reference marker using the collectors.

Define the Translational and/or Rotational Properties of Forces

Force/torque properties can be defined along/about three axes of the local reference marker using the Fx/Tx, Fy/Ty, and Fz/Tz fields in the Properties tab. In case of a Line of Action translational force, the line defines the direction of application and the property can be defined in a single field provided. The same is true for a Single Component Rotational torque.

  1. Click either the Trans Properties tab or the Rot properties tab.
    The Trans Properties tab is displayed when the selection in the Properties drop-down menu in the Connectivity tab is set to either Translational, TransRotational, or Line of Action Translational.
  2. Specify how to define the translational/rotational properties in each direction using the drop down menus.
    If Linear is chosen, enter a constant value of displacement, velocity, or acceleration.
    If Curve is chosen:
    1. Select AKIMA, CUBIC, LINEAR , or QUINTIC under Interpolation as the method of interpolation of between two data points in the curve.
    2. Enter a value under Independent variable.
    3. Resolve the curve by double-clicking the Curve collector and selecting a curve from the Select a Curve dialog.
      Note: To use a curve, you first need to define a curve (using the Curves panel) which represents the behavior of the force.
    If Spline3D is chosen:
    1. Select AKIMA, CUBIC, LINEAR, or QUINTIC under as the method of interpolation of values between two data points in XY plane.
    2. Resolve the 3D spline by double-clicking on the Spline3D collector and selecting a Spline3D entity from the Select a Spline3D dialog.
      Note: To use a Spline3D entity, you first need to define a spline using the Spline3D panel.
    3. Specify an expression for Independent variable X and Independent variable Z.
    If Expressions is chosen, enter a solver expression to define displacement, velocity, or acceleration.
  3. Repeat the same step for the second properties tab if needed.

Use User-Defined Properties for a Force

If desired, define the force using the User-Defined tab, which will allow you to specify the properties of the force using user subroutines.

  1. From the Connectivity tab, click the User-defined properties check box.
    Other Properties tabs are removed.
  2. Click the newly added User-Defined tab.
  3. Define the user subroutine.
    1. Provide an expression with the USER solver function with parameters being passed to the user subroutine.
    2. Alternatively, activate the Use local file and function name check box to specify a local file where the subroutine code can be accessed by the solver.
      If this option is not specified, MotionSolve will search for a subroutine following its user subroutine loading rules.
    3. Select a function type from the drop-down menu.
    4. Select the local file for the subroutine.
      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).
    5. Specify the function name in the subroutine that defines the entity, or accept the default name provided by MotionView.

Define a Non-linear Property Using a Curve

An interpolation method and an independent variable are required to define a Fx, Fy, Fz curve. The interpolation method determines how the solver computes y values on the curve between data points. There are three interpolation methods:
  • Cubic
  • Linear

The CUBIC and AKIMA interpolators are spline functions that are evaluated internally by the solver. The LINEAR interpolator is implemented using a series of IF statements.

The independent variable of the curve is specified after an interpolation method is selected. For example, for a non-linear spring, the independent variable of the curve is typically the deflection of the spring. The independent variable in a non-linear property varies during the solution and is usually written in the form of an expression. Expressions allow you to use any formula to define the independent variable. MotionView provides an appropriate default expression for the independent variable for most springs, bushings, and forces.

  1. If the Forces panel is not currently displayed, select the desired force by clicking on it in the Model Browser or in the modeling window.
    The Forces panel is automatically displayed.
  2. Select Curve from the Property drop-down menu.
    The Value text box becomes a collector.
  3. Double click the curve collector to display the entity selector for curves.
  4. Select a curve.
  5. Select an interpolation method.
  6. Specify the independent variable of the curve.