You can analyze the contacts and boundary conditions of bodies to verify that bodies are sufficiently constrained. You can view animations of the model based on the active degrees of freedom, and identify bodies that are under constrained before you run a simulation.
To detect unconstrained bodies:
In a static study, open the Contact Visualization Plot PropertyManager, and click the Underconstrained bodies tab.
The enhanced algorithm detects the active degrees of freedom (DOF) for each body, and helps you visualize the parts in a model that exhibit translational or rotational rigid body modes.
Click Calculate to detect bodies that are not sufficiently constrained, and exhibit translational or rotational rigid body modes. The analysis tool applies a coarse mesh and runs the static study (using the Direct Sparse Solver) with all defined loads, contacts, and boundary conditions.
If the analysis tool detects bodies that can translate or rotate freely exhibiting rigid body modes, it lists these bodies and the directional active degrees of freedom (translations and rotations) under Underconstrained bodies.
Select one of the listed degrees of freedom (for example, Translation 1 or Rotation 1) to view an animated translation of the under constrained body. A green arrow in the graphics area points to the direction of free movement.
If no rigid bodies are detected, the solver issues a message that the model is fully constrained.
The Underconstrained bodies tool does not detect any instability issues for models containing no penetration contacts, or bolt connectors. Bodies with bolt connectors and no penetration contacts can be sufficiently constrained for a successful simulation, but they are shown in the list of underconstrained bodies.