Activity-Deletion Criteria

After a contact has been created, it will contain a contact model that provides a particle-interaction law to update the internal force and moment. The contact also has an activity state. If the contact is active, then the particle-interaction law is entered; otherwise, the internal force and moment are set to zero. A contact model can set the activity state (e.g., making a contact inactive will bypass the particle-interaction law and thereby increase computational speed). The activity criterion provides the condition for which the contact will be active; otherwise, the contact will be inactive.

The contact detection logic determines (based on body proximity) when a contact can be deleted; however, a contact model can prevent a contact from being deleted. The deletion criterion provides the condition that must be satisfied to allow the contact to be deleted at the discretion of the contact detection logic.