General Contact Settings (Nonlinear)

Contact Element Updating Tab

For general surface-to-surface contact in nonlinear analyses, the contact elements in the model are updated periodically during the solution (by default). The purpose is to accommodate rigid body motion and to confine the solver to considering contact only where surfaces are close together. Regions with surface contact defined, but that are far from neighboring contact regions, can thus be ignored.

The following Contact Element Updating options are available:

• Automatic: The surface-to-surface contact process determines which areas of a contact surface may come into contact during each time step and only generates contact elements in these areas. On a different time step, different areas may be in or near contact, so the automatic updating adds elements where needed and removes elements where not needed. For example, imagine two meshed gears. Although all teeth on the pinion are defined as contacting all teeth on the gear, at time T=1 only the teeth currently in contact need contact elements. Evaluating contact at the other teeth would simply increase the analysis time, so those contact elements are removed from the solution. At a later time (T=2), different teeth are in contact, so a different area is where the contact elements are created. If the Automatic option is selected, the distance criterion (contact radius) and the updating frequency are varied according to the relative motion of the two contact surfaces. A linear acceleration assumption is used to calculate the contact radius. A frequency of 10 times per second is used as the initial frequency of updating the contact areas.
• Never: When this option is selected, the contact elements are generated for all areas and are not subsequently updated during the solution. This method is only recommended for models with clearly defined contact regions that experience very small motion relative to the mesh size. The advantage is that the processor does not use any time to decide when to add or remove contact elements from the solution, so this time is saved during the solution.
  Tip: If using the Never option, also consider minimizing the number of contact elements created by specifying a Maximum initial distance (applicable to the SimMech solver only). See the Geometry Tab section of the page, Simulation Mechanical Surface Contact Options (Nonlinear).
• User-defined: When this option is selected, you need to specify how often the process should update the contact elements. Do so in the Frequency input field. The units of the updating frequency depend upon the currently active time unit of your model [updates per second (or Hertz), updates per minute, or updates per hour based on the event time line].
  Important: You must also specify the contact search radius for the processor to use in determining where to create contact elements. You must define the search radius for each individual contact pair using one of the following methods, depending on the solver you will use:

  Select one or more individual contact pair headings in the browser. Then, right-click a selected heading and choose Edit Settings from the context menu. Next...

  • For the native Simulation Mechanical solver, select SimMech contact options from the drop-down menu at the top of the Contact Options dialog. Then, specify a value in the Contact interaction distance field within the Geometry tab.
  • For the Nastran solver, select Nastran contact (BSCONP) options from the drop-down menu at the top of the Contact Options dialog. Then, specify a value in the Maximum activation distance field within the General tab .