Each contact element type includes a number of key options (KEYOPTs) that control contact algorithms and other settings. General contact uses some of these key options in the same way as pair-based contact. However, some key options may be set to a different value by the GCGEN command, or they may not be used by general contact. The table below summarizes the contact element key options and how they are used differently for pair-based contact and general contact.
Table 8.1: KEYOPT Settings for Pair-Based vs. General Contact
| KEYOPT | Description | Pair-Based Contact Default | General Contact Default | Comments for General Contact Usage |
|---|---|---|---|---|
| 1 | Selects DOF | Manual | Automatic DOF selection based on underlying elements | Not applicable to CONTA175 and CONTA177 |
| 2 | Contact Algorithm | Augmented Lagrange | Penalty | GCGEN sets KEYOPT(2) = 1 |
| 3 (CONTA172 and CONTA174) | Unit control for normal contact stiffness | No unit control | n/a | This KEYOPT is not supported |
| 3 (CONTA175) | Vertex contact type | Contact force-based model | Contact traction-based model | GCGEN sets KEYOPT(3) = 1 |
| 3 (CONTA177) | Beam/edge contact type | Parallel beams | Mixed parallel and crossing beams | GCGEN sets KEYOPT(3) = 2 |
| 4 | Location of contact detection point | KEYOPT(4) = 3 and 4 are not supported for CONTA177 | ||
| 5 | CNOF/ICONT adjustment | No adjustment | No adjustment | |
| 6 | Contact stiffness variation | Use default range | Use default range | |
| 7 | Element level time increment control | No control | No control | KEYOPT(7) = 4 is not supported |
| 8 | Asymmetric contact selection | No action | n/a | This KEYOPT is not used and is replaced by
GCDEF,Option |
| 9 | Effect of initial penetration or gap | Include all | n/a | This KEYOPT is not used and is replaced by
TBDATA,,C1. The
default behavior is to exclude effects of initial
penetration/gap |
| 10 | Contact stiffness update | Between iterations | Between iterations | GCGEN sets KEYOPT(10) = 0 |
| 11 | Beam/shell thickness effect | Exclude |
Include for CONTA172 and CONTA174 Exclude for CONTA175 |
GCGEN sets KEYOPT(11) = 1 for CONTA172 and CONTA174 KEYOPT(11) = 1 for CONTA177 when the underlying elements are beams |
| 12 | Behavior of contact surface | Standard | n/a | This KEYOPT is not used and is replaced by
TB,INTER,,,TBOPT |
| 13 | Degree of freedom control for contact involving thermal shells | TEMP | n/a | This KEYOPT is not supported |
14 (CONTA172 and CONTA174) | Behavior of fluid penetration load | Iteration-based | n/a | This KEYOPT is not supported |
14 (CONTA177) | Multiple target segments | One segment | Four segments | GCGEN sets KEYOPT(14) = 1 |
| 15 | Effect of stabilization damping | Active only in first load step | Active only in first load step | |
| 16 | Squeal damping controls | Damping scaling factor | n/a | This KEYOPT is not supported |
| 18 | Sliding behavior | Finite sliding | Finite sliding |
The default settings assigned by GCGEN are the recommended settings. They are suitable for most contact simulations. For some specific applications, you may need to override the defaults. Use the KEYOPT command to define non-default settings for a specific general contact surface identified by a unique element type ID:
KEYOPT,ITYPE,KNUM,VALUE
If you do not know the element type ID (ITYPE), you may
prefer to input a node component that contains nodes on the surface of interest. See
Identifying General Contact Surfaces for details.
In the following example, the projection-based contact formulation is specified for a surface that is identified by an element type ID associated with a predefined nodal component:
KEYOPT,ComponentName,KNUM,VALUE
An extension can be added to the component name to limit the scope of the element type IDs used from the node component, as described in Specifying General Contact Interactions Between Nodal Components. The labels ALL_EDGE, ALL_FACE, ALL_VERT, ALL_TOP, and ALL_BOT can also be input on the KEYOPT command to identify the general contact surface. (See the GCDEF command for details of the meaning of each label.)
To set an element key option for all contact element types in the general contact
definition, input the label GCN instead of an ID number in the
ITYPE field:
KEYOPT,GCN,KNUM,VALUE
The above command must be issued after the GCGEN command.
You can define general contact elements manually using the ESURF command instead of using GCGEN. However, contact elements created by ESURF use the pair-based default settings. You should consider changing the settings manually for these elements so that they correspond to the general contact default values.