Modal Forces

The Modal Forces tool allows you to include a disturbed force on a flexible body that exists in the modal form in the flexible body H3D.

Create Modal Forces

From the Model Browser, select the system to which the Modal Force entity is to be added.
Right-click on a system in the Model Browser and select Add > Force Entity > ModalForce from the context menu.
OR

Right-click on a modal force folder in the Model Browser and select Add ModalForce from the context menu.

OR

From the Model ribbon, click the arrow next to the Entities tool set name, then select Modal Forces.

The Add ModalForce dialog is displayed.
Specify a label for the force.
Specify a variable name for the force.
By default, variables names of entities in MotionView follow a certain convention. For example, all modal force entities have a variable name starting with “mfrc_”. This is the recommended convention to follow when building models in MotionView since it has many advantages in model editing and model manipulation.
Click OK to close the window or Apply to continue creating entities.

Note: In order to add a distributed force on a flexible body, the force needs to be included in the flexible body H3D during the CMS flex body generation process. The force can be a generic force on a set of nodes, or a pressure load on a set of elements or a thermal loading.
Once the force is available in the flexible body, the force can be scaled with regard to time or a solver function expression using the Properties tab.

Once a modal force entity has been added to the model, the panel for the force will automatically be displayed in the panel area.

Edit Modal Forces

Define the Connectivity of Modal Forces

From the Connectivity tab, select the flexible body on which the distributed force should be applied.

If the Modal Force panel is not currently displayed, select the desired modal force by clicking on it in the Model Browser or in the modeling window.
The Modal Force panel is automatically displayed.
Click the FlexBody collector and select the flexible body on which the distributed force is to be applied from the modeling window, or double click the collector to open the Model Tree (from which the desired body can be selected).
Select the force type from the drop-down menu.
For the MotionSolve solver mode, this force can be applied only as an action only force. For the ADAMS solver mode, the force can also be applied as action reaction. In this case, an additional option to specify a rigid body as reaction body is available.
If Action Reaction is chosen as the force type, click the RigidBody collector and select a rigid body as a reaction body for the distributed force from the modeling window or Model Tree.

Define the Properties of Modal Forces

From the Properties tab, the load case that is available in the flexible body H3D can be selected and a scale factor can be applied.

Select the method of scaling for the modal force from the drop-down menu.
If Linear is chosen, enter a real number in the value field to specify the constant scale.

If Curve is chosen, define the scale in the form of a curve.
1. Select AKIMA, CUBIC, LINEAR , or QUINTIC under Interpolation as the method of interpolation of between two data points on 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.
If Spline3D is chosen, define the scale as a function of two independent variables in the form of a three dimensional spline data.
1. Select AKIMA, CUBIC, LINEAR , or QUINTIC under as the method of interpolation of values between 2 data points in XY plane.
  The interpolation choices are applicable to Independent variable X only. Data along Independent variable Z is linearly interpolated.
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 Expression is chosen, define the scale in the form of a solver function.
Select the load case from the drop-down menu.
The list contains the load case id as available in the flexible body H3D. Load case ID generally matches with the ID specified in the finite element deck (.fem in case of OptiStruct) that was used to generate the flexible body.

Use User-Defined Properties for a Modal Force

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

From the Connectivity tab, click the User-defined properties check box.
The Properties tab is removed.
Click the newly added User-Defined tab.
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.