**Type Trajectory**When a 2D model contains unstructured Lagrangian volume elements the 2D trajectory must be used to define Lagrange/Lagrange Interactions.

An analysis model that contains a mix of structured (IJK) Lagrangian Parts and unstructured Lagrangian Parts can currently not be run with Trajectory contact and also not with Gap contact.

To be able to use Trajectory contact the analysis model must contain unstructured Lagrangian volume Parts only. Similar, to be able to use Gap contact the analysis model must contain structured Lagrangian Parts only.

**Method**Method in which a contacting node is pushed back to the true contact position during the computational cycle.

There are three methods available:

**None**No contact defined

**Penalty**If a contact event is detected, a local penalty force is calculated to push the node back to the face. Equal and opposite forces are calculated on the nodes of the face in order to conserve linear and angular momentum. The applied penalty force will push the node back towards the true contact position during the cycle. However, it will take several cycles to satisfy the contact condition. Kinetic energy is not necessarily conserved. The conservation of energy can be tracked using the energy time history.

**Decomposition Response (DCR)**All contacts that take place at the same point in time are first detected. The response of the system to these contact events is then calculated to conserve momentum and energy. During this process forces are calculated to ensure that the resulting position of the nodes and faces does not result in further penetration at that point in time. The decomposition response algorithm is more impulsive (in a given computational cycle) than the penalty method. This can give rise to large hourglass energies and energy errors.

**Retain inertia of eroded nodes**Check this box if you want to retain the inertial of eroded nodes (otherwise eroded nodes are removed from the model).

**Interaction by Part****Add**Sets interactions between Parts.

**Add All**Sets all Parts to interact with each other.

**Remove**Removes interactions between Parts.

**Remove All**Removes all interactions between Parts.

**Matrix**Sets interactions using a Part matrix.

**Friction**Sets static friction coefficients between different Parts.

**Review**Enables a review of all of your interaction settings.

**User defined friction**Aside from the friction definition through the Interaction by Part method described above there is also a user defined friction option available through the use of a user-subroutine called EXFRICTION2D.

**Self Interaction**If the self-interaction option is switched on the contact detection algorithm will also check for external nodes of a part contacting with faces of the same part in addition to other parts. This is the most robust contact setting since all possible external contacts should be detected.

**Self-interaction Tol**The self-interaction option enables automatic erosion when an element deforms such that one of its nodes comes within a specified distance of one of its faces. This option will prevent that volume elements become degenerated.

The specified distance is calculated using the Self-interaction Tol. value which is a factor in the range 0.1 to 05. This factor is multiplied by the smallest characteristic dimension of the elements in the mesh to give a physical dimension.