General Contact Pairs
General contact pairs () are only used by General Contact nodes.
Contact Selection
A General Contact node can reference any number of general contact pairs. However, when adding a General Contact Pair, the contact selection is set to include all objects. A single pair is then sufficient to define contact interactions between all geometric objects in the model. In most cases, this is the intended behavior.
For complex or large models there are situations where you may want to take manual control of the contact selection. A typical example is fluid–structure interaction and similar multiphysics. Here you want to exclude the fluid domains from the general contact pair to correctly identify the exterior boundaries of the solid objects.
Other cases are when you know that some parts of the model may not be of interest for contact analysis or never interact. The cost of the contact analysis can then be reduced by using a general contact pair with a manual selection for each region.
Lastly, if some boundaries cause difficulties with convergence for the contact analysis they can be omitted by using a manual control of the contact selection.
In all above cases, when using a manual contact selection, the resulting source and destination boundaries are set up from the union of the exterior boundaries of the selected domains and the selected boundaries.
The selection of a general contact pair often intersects with the selection of other pairs in the model. While this is not an issue in most cases, it may cause interactions that are either unnecessary to compute or even unphysical. To avoid this, it is possible to exclude boundaries from other pair types in the source and destination boundaries generated for the general contact pair. By default, destination boundaries from other pair are excluded but it is also possible to exclude source boundaries from other pairs.
Small Sliding Contact
In some situations, the relative sliding between the boundaries in contact is small. This is, for example, often the case for shrink fit simulations, when mounting a component using prestressed bolts.
The sliding distance can be considered small if it is significantly less than the length of a mesh element edge. In such a case, it is possible to simplify the problem by selecting the Mapping Method to be Initial Configuration in the General Contact Pair node. With this setting, a point on the destination boundary is mapped to the same point on the source boundary throughout the entire simulation; that is, the mapping is constant. This setting will make the contact analysis run faster and be more stable.
The analysis is geometrically nonlinear also when using this option, and the contact region can still have arbitrarily large displacements and rotations.
Friction can be modeled. Even though there is no sliding in a geometrical sense, the difference in tangential displacement is computed.
You cannot mix contact pairs with the two different types of Mapping Method within the same General Contact node.