Add/Edit Motion Contacts

Create or edit motion contacts between parts or sets of parts.

Sets are used to simplify creation of contacts, as shown in the following examples. You would typically define contacts by selecting parts one by one, but you can use a different method of selection such as By Material or By Rigid Group to quickly select several parts with a single click.
Figure 1. Example 1: All parts are placed in the red set.
Figure 2. Example 1: Contacts are created between every possible combination of parts in the red set. (The image below shows what you see when the Individualize option is selected.)
Figure 3. Example 2: Parts are placed into both the red and blue sets.
Figure 4. Example 2: Contacts are not created between parts in the same set, but are established between parts in the different sets.
  1. Select the Contacts tool.

  2. Use the menu to apply options such as friction or the collision type before creating the contacts. You can also exclude design spaces and ground parts from part selection.
  3. Optional: Adjust the skin mesh resolution for contacting parts.
    1. Click the Show/ Hide Mesh icon, then select parts where you would like to change the mesh.
    2. Use the microdialog options to change the skin mesh resolution.
      Note: The mesh preview is not available for MotionSolve analytical shapes (such as spheres, boxes, cylinders, ellipsoids, or frustums) or for flexible bodies. If you try to preview the mesh for analytical-based parts or flex bodies, a label that reads Analytical Shape, or Flex Body will replace the mesh resolution microdialog options.
      Option Description
      Very Low Very Low produces a larger element size and lower mesh density.
      Low  
      Medium (default)  
      High  
      Very High Very High produces a smaller element size and a higher mesh density.
      Note: ​ A Very High mesh resolution may not produce better results than a Very Low resolution. For best results, try to minimize the difference between the mesh densities as much as possible.
    3. Right-click and mouse through the check mark to exit or double-right-click.
  4. Select what method to use to place parts into sets using the guide bar.

  5. Select parts to place in the first set. Use the Ctrl key to add or remove parts to a set. The part counters on the guide bar are updated as you add and remove parts from the sets.
    Method Part Selection
    By Parts Select parts one by one to add to them to a set.
    By Connection Hover the mouse over the model; parts that are connected together will be prehighlighted. Click it, and these parts are added to the set.
    By Material Hover the mouse over the model; parts that have been assigned the same material will be prehighlighted. Click it, and these parts are added to the set.
    By Assembly Hover the mouse over the model; parts that belong to the same assembly will be prehighlighted. Click it, and these parts are added to the set.
    By Rigid Group Hover the mouse over the model; parts that belong to the same rigid group will be prehighlighted. Click it, and these parts are added to the set.
    At Free Joints This method finds part pairs associated with free joints. Use the navigation arrows on the guide bar to jump from one part pair to the next. When using this method, both sets are populated for you. If there are no free joints in your model, no part pairs are presented.
    At Cylinders and Holes This method models solid cylinders inside circular holes with an analytical solution rather than a mesh-based solution. Using geometric primitives like this can improve the efficiency of the solution.
  6. When using a second set, click Parts2 on the guide bar and select parts to place in the second set.
    Note: You can use different methods to define the red and blue sets. For example, you can use By Materials to define the first set and By Parts to define the second set.
  7. Optional: To create individual contacts between part pairs, select the Individualize check box. (This option can also be applied after a contact has been created.)
  8. Optional: Find and review initial intersections between contacting parts.
    Note: Initial intersections between parts can present difficulties in solving contact models and affect the accuracy of results. It is not mandatory that the intersections be removed before running the simulation; a contact model with some minor overlaps may still solve without having any adverse effect on results. Plotting the initial contact force and contact penetration can help you decide whether the intersection should be removed. However, if parts defined in a contact are intersecting at the start of the simulation, it could cause the simulation to run more slowly and/or display erratic behavior between the contacting parts.
    1. First, make sure that the following criteria are met:
      • There must be a contact defined between the parts.
      • The contacting parts must be visible.
    2. On the guide bar, click Find Initial Intersections.
    3. A new guide bar appears. The first button says Intersections (n), where n equals the number of intersections found. To review the intersections, click the following buttons:
      • Go to Next: Go to the next intersection.
      • Go to Previous: Go to the previous intersection.
      • List Intersections: Display the Intersection Table, which lists the intersecting parts of all visible motion contacts in the model. Click on a name in the table to review the corresponding intersection in the modeling window.

    One part has a blue dotted outline, while the other part has an orange dotted outline. The intersection is displayed in red.

  9. Click the Apply button on the guide bar.
    This creates a single motion contact, unless Individualized was selected.
  10. Select a contact to edit it. Use the microdialog to change the contact's collision type or to enable friction.
  11. Right-click and mouse through the check mark to exit, or double-right-click.
Tip:
  • Refer to Best Practices for Motion Contacts for additional guidance when applying motion contacts to your model.
  • The plotting feature for motion contacts is only available if they have been individualized.
  • When using the At Free Joints option, Inspire will automatically detect Free Joint candidate pairs and zoom in on the first detected pair. You can create motion contacts at free joints very quickly by holding the Ctrl key while clicking Apply on the guide bar. This will create the contact pair and automatically navigate to the next detected pair.
  • When using the At Cylinders and Holes option, Inspire will automatically detect Cylinder and Hole candidate pairs and zoom in on the first detected pair. You can create motion contacts at cylinders and holes very quickly by holding the Ctrl key while clicking Apply on the guide bar. This will create the contact pair and automatically navigate to the next detected pair.
  • Hold Ctrl while clicking the Motion Contacts icon on the ribbon to enter editing mode. This will edit the most recent contact that was created. To edit multiple contacts simultaneously, select multiple contacts in the Model Browser before selecting the Motion Contacts tool.
  • You can visualize your motion contact forces using the Force Explorer.
  • Suppress/Unsuppress a motion contact to understand its effect on your model. On the contact, right-click and select Suppress. From the Model Browser or Table, right-click and select Unsuppress.

Find Options

Click the menu on the guide bar to apply global options before creating motion contacts.

Enable Friction
Enable this option to include forces that arise from frictional effects.
Collision Type
Select a collision type - Impact (default), Poisson, or Volume.
Force Computed At
Select whether the contact normal force is applied at the nodes or the element center when parts come into contact.
Exclude Design Spaces
Enable this option to prevent design spaces from being selectable.
Exclude Ground
Enable this option to prevent ground parts from being selectable.
Exclude Skewed Holes
Enable this option to prevent skewed holds from being selectable.

Microdialog Options

Use the options in the microdialog to edit the motion contact.

Option Description
Enable Friction   Enable this option to include forces that arise from frictional effects. Click the to view additional options.
Static coefficient
The static coefficient of friction, which has to be overcome by a body before it can move.
Dynamic coefficient
The dynamic coefficient of friction, which the body experiences while in motion
Stiction transition velocity and Friction transition velocity
In our friction model, a smooth transition must be made between the friction coefficients (static and dynamic). The transition velocities let you control the sharpness of this transition. When the slip velocity is between stiction transition velocity and friction transition velocity, the coefficient of friction is in transition between the two. The default values are good for most models, but you may need to change them if you're trying to correlate with physical tests.
Collision Type

Select a collision type for the normal force calculation. Click the to view additional options.

Impact (default)

Stiffness:
The stiffness of the boundary surface interaction. You can enter the Stiffness value in your preferred units set and the nonlinear effect of the Exponent parameter will be accounted for automatically.
Damping
The maximum damping coefficient.
Penetration depth
The depth beyond which full damping is applied.
Exponent
The exponent on penetration depth in the force-penetration depth characteristic of the contact interface.
  Poisson
Penalty
Determines the local stiffness properties between materials. Larger values lead to reduced penetration between two bodies.
Coefficient of restitution
Represents the energy loss between the two parts in contact. The valid range for this value is between 0.0 and 1.0. A value of 1.0 represents no energy loss and a perfectly elastic contact. A value of 0.0 represents a perfectly plastic contact and all energy is dissipated during contact.
Normal velocity
Velocity limit after which full damping force is applied.
  Volume
Material layer depth
The layer depth of material. This is used to calculate the contact stiffness.
Damping
The damping coefficient value used to calculate the damping force.
Exponent
The exponent of the force deformation characteristic.
Force Computed At  
Element Center
When parts come into contact, the contact normal force is applied at the element center.
Nodes
When parts come into contact, the contact normal force is applied at the nodes of the element.
Reset  
All Defaults
Restore all default settings.
Visible Defaults
Restore default settings only for options currently visible in the microdialog.

Motion Contact Properties

Use the following properties in the Property Editor to refine motion contacts.

Precise Contact Event
If you enable this property and enter a tolerance, the solver will more precisely determine when two parts come into contact. Enabling this option will improve the accuracy and robustness of motion contact simulations, but will also increase simulation time, so it should be used only when necessary.
Refine Step Size
If you enable this property and enter a new step size, the solver will use it as the maximum step size for the simulation after the contact is detected.
Keep Force Results

This option allows you to limit the number of contact forces that are stored in the model after motion analysis. The choices for an individual motion contact are: Default, All, Region Only, and None.

  • Default: This setting uses the option selected on the Motion Analysis Settings window under Contacts. (This is a global setting, whereas the options set in the Property Editor apply to individual motion contacts.)
  • All: Select this option to include both the individual forces and the summed contact forces.
  • Region Only: This option excludes individual forces and gives you forces that have been summed at their respective contact regions. Region only forces correspond to the Sum Forces: At contact region option on the Force Explorer.
  • None: Select this option to keep no force results for the selected motion contact. This helps to reduce the size of the .stmod file because you are storing less data.

If you choose Region Only or None, be aware that when animating motion results with the Force Explorer, you will only see the level of content you specified for a given contact. For example, if you choose Region Only you will not see the individual (unsummed) force vectors. Likewise, you would not see any of the force vectors due to contact if you select None.

Tip: Sometimes you may want to temporarily turn off or ignore a contact while debugging your model. You can disable all motion contacts in the model using the Contacts option in the Run Motion Analysis window.

Motion Contacts Table

The Motion Contacts table lists all of the motion contacts in your model including the parts in each contact set and various other parameters.

Location: Motion Contacts tool, satellite icon

Figure 5. Motion Contacts Table
To Do this
Rename a motion contact Select the cell in the table and then click again to make the field editable.
Change the collision type Select the cell in the table and then select a different option from the list.
Edit a parameter Select the cell in the table and then click again to make the field editable.
Sort a column Click the column header. Click repeatedly to toggle between ascending and descending order.
Add or remove columns Right-click on a column header.

Analytical vs Mesh-Based Contacts

If motion contact sets contain parts that are detected as box primitives, the solution between the box and other analytical shapes (sphere, cylinder, and frustum) is analytical rather than mesh based. Using geometric primitives in these cases generally improves the efficiency of the solution. The following table shows when an analytical vs. mesh-based solution is used:

  SPHERE BOX ELLIPSOID CYLINDER FRUSTUM MESH
SPHERE Analytical Analytical Analytical Analytical Analytical Semi
BOX   Mesh Mesh Analytical Analytical Mesh
ELLIPSOID     Mesh Mesh Mesh Mesh
CYLINDER       Analytical Analytical Mesh
FRUSTUM         Analytical Mesh
MESH           Mesh

When using the analytical method, each of the contacting geometries is represented by an analytical expression, whereas with the mesh method both geometries are tessellated. Semi indicates that one of the geometries is represented analytically, while the other is tessellated.

Shortcuts

To Do this
Select/deselect part Click
Advance from the first set to the second step Right-click
Create contact Right-click (both sets must be populated)
Advance from one part pair to the next When using the At Free Joints option, use the arrow keys on the guide bar to quickly navigate from one part pair to the next. Hold Ctrl while clicking Create on the guide bar to quickly create and advance to the next pair.
Edit a contact Hold Ctrl while clicking the Motion Contacts icon on the ribbon.
Edit multiple contacts Select multiple contacts in the Model Browser, then click the Motion Contacts icon on the ribbon.
Exit the tool Right-click and mouse through the check mark to exit, or double-right-click.