contact_geometry index geometry_entity_item geometry_entity_index

This record specifies a contact geometry. Contacting nodes are forced to stay at the outward normal side of the contact geometry.

The allowed geometries and their material outward normals are listed below

• If a geometry_point is used in 1D, the normal is in positive x-direction.
• If a geometry_line is used in 2D, the normal is the outer product of 3-direction and the line direction (from point 0 to point 1).
• If a geometry_circle is used in 2D, the normal is the outward direction at the circle.
• If a geometry_ellipse is used in 2D, the normal is the outward direction at the ellipse.
• If a geometry_sphere is used in 3D, the normal is the outward direction at the sphere.
• If a geometry_polynomial is used in 2D, the normal is in positive y-direction.
• If a geometry_polynomial is used in 3D, the normal is in positive z-direction.
• If a geometry_triangle is used in 3D, the normal is in direction of the outer product v01 $*$ v02 where v01 is the vector from node 0 to node 1 and v02 is the vector from node 0 to node 2.
• If a geometry_quadrilateral is used in 3D, the normal is in direction of the outer product v01 $*$ v02 where v1 is the vector from node 0 to node 1 and v02 is the vector from node 0 to node 2. Only non-distorted quadrilaterals should be used.

This normal can be switched sign by setting the contact_geometry_switch with the same index to -yes.

In stead of geometries, also contact with all elements will be checked. Only contact with the elements -bar2, -tria3, -quad4, -tet4 and -hex8 can be detected. The outer boundary of the elements should be specified by node_boundary records. Often it is sufficient to apply node_boundary records on the body with the coarsest mesh; if the meshes of the contacting bodies are of the same size however, you should specify node_boundary records for both contacting bodies.

The time steps should be such small, that contacter nodes penetrate the other elements only in small steps.

If a contact_geometry is used, then the contacter node should also be within the tolerance of the geometrical entity to be noticed!

If contact is detected, normal contact forces of size contact_penalty_velocity $*$ penetration are generated between the contacting node and the other element. Moreover, also a frictional force of size friction $*$ normal force is generated (see contact_friction).

You need more iterations, see control_timestep_iterations, then normal; say 5 or more.

As an alternative to the contact algorithm, see slide_geometry.