Use a Contact Pair node () to specify two selections of boundaries to be used for contact modeling. A contact pair defines boundaries for parts in an assembly that can come into contact under deformation. The pair establishes a mapping between points on the source and destination boundaries by performing a contact search. For more information about mechanical contact modeling and guidelines for selecting source and destination boundaries for contact pairs, see the Structural Mechanics Module documentation.

This section is the described for the Identity Pairs except that the default Pair type is Contact pair.

To define the source or destination boundaries, from the Selection lists, choose Manual, All boundaries, or any other available selection for the boundaries on the source or destination side. If Manual is selected, click in the Graphics window to add boundaries to the Selection section. If required, click the Swap Source and Destination button () to swap the source boundaries and the destination boundaries.

Click the Active button to toggle between turning ON and OFF selections directly in geometry, for example. Such selections also become active when you choose Manual from the Selection list.

The contact search can be split into two steps: a broad search and a fine search. The purpose of the broad search is to cheaply identify a subset of the source mesh in which the mapped point could be located. The fine search is done for this subset only, and aims to identify the exact coordinates of the source point to set up a source-destination point pair for which expressions can be mapped. By selecting a Search method, the algorithm used for the broad search can be controlled. It defaults to Hierarchical in 2D and 3D components, and to Distance Tracking in 1D components. The fine search is the same for all search methods. It uses a ray tracing algorithm to identify the point of the source mesh that first intersects a ray shoot in the direction of the normal to the destination point.

For each destination point, the Hierarchical search method identifies a subset of the source mesh that intersects a line segment within the specified search distance. The direction of the line is given by the normal at the destination point. By utilizing hierarchical data structures, this can be done efficiently and in a way that scales well with the number of mesh elements of the source boundaries.

The Distance tracking method keeps track of the distance from each destination point to the source mesh. If the distance becomes smaller than the specified search distance, a contact search is performed for that point. The contact search loops over all source elements, and if an element is detected inside a ball centered at the destination point, a fine search is performed. The radius of the ball is updated adaptively during the search.

The Exhaustive search method always performs a fine search for all mesh elements of the source for each destination point. This can be expensive for large models, but guarantees that the correct source-destination point pair is always found.

Both the Hierarchical and Distance tracking methods have internal logic to speed-up the broad search. The only reason for using the Exhaustive method is if this logic leads to an incorrect mapping, that is, if it is obvious that an incorrect source-destination point pair is found.

The Mapping method list is by default set to Deformed configuration. This setting means that whenever the source or destination has moved, a new search for possible contact points is made. If you know that the movements of the source and destination are small, selecting Initial configuration can be more efficient. In this case, a pairing between source and destination points is computed based on the initial configuration and always stays the same. This approach works well if the distance between source and destination is initially smaller than the search distance, and movements in the tangential direction are small.

The contact search is performed by searching for points on the source and destination that have a distance that is less than the search distance. By default, the search distance is determined automatically as 1% of the diagonal of the geometry’s bounding box. To tune it manually, choose Manual from the Search distance list and enter a value in the Distance field (SI unit: m). Using a larger search distance can be needed when the geometry has a large gap between source and destination.

You can use the Extrapolation tolerance setting (a fraction of the element length; default 10−4) to effectively extend the source and destination boundaries slightly outside the selections. The size of this extension is equal to the extrapolation tolerance multiplied with the mesh element size.