Manual contact regions represent contact over the entire extent of the contact scope, for example, faces of the contact region.
Automatic contact regions represent contact only to the extent of the scope where the corresponding bodies initially are close to one another. For automatic contact, the contact elements are "trimmed" before solution. The trimming is based on the detection tolerance. The tighter the tolerance, the less number of generated contact elements. Note that if you set Large Deflection effects to On in the Details view of a Solution object, no trimming will be done due to the possibility of large sliding.
Valid reasons to manually change or add/delete contact regions include:
Modeling "large sliding" contact. Contact regions created through auto-detection assume "assembly contact," placing contact faces very near to one another. Manual contact encompasses the entire scope so sliding is better captured. In this case, you may need to add additional contact faces.
Auto-detection creates more contact pairs than are necessary. In this case, you can delete the unnecessary contact regions.
Auto-detection may not create contact regions necessary for your analysis. In this case, you must add additional contact regions.
You can set contact conditions manually, rather than (or in addition to) letting the application automatically detect contact regions.
Within a source or target region, the underlying geometry must be of the same geometry type (for example, all surface body faces, all solid body faces). The source and target can be of different geometry types, but within itself, a source must be of the same geometry type, and a target must be of the same geometry type.
To set contact regions manually:
Select the Connections object in the Outline.
Right-click and select Insert > Manual Contact Region. You can also select the option on the Context tab.
A Contact Region item appears in the Outline. Click that item, and under the Details Pane, specify the Contact and Target regions (faces or edges) and the contact type. See the Contact and Target topics in the Scope Settings section for additional Contact Region scoping restrictions.