Designers often want to analyze models in which parts are held together by contact alone with no additional constraints. Gaps may be present in the beginning of the analysis due to CAD clearances or during the nonlinear solution, causing the solution to fail. Even in the absence of gaps, rigid body modes may not be suppressed if the interfaces are frictionless, and the problem may fail to converge.
If the static solution does converge, the results may be inaccurate or machine-dependent. This can occur because the equation solver encounters an extremely small (near zero) pivot that escapes the tolerances used by the program to identify zero pivots.
To achieve a static solution for underconstrained problems, the following stabilization methods are recommended:
Add weak springs
Activate nonlinear stabilization
Activate contact stabilization
Alternatively, these full transient solution methods can be used to achieve a static-like response:
Full transient solution with the quasi-static setting
Full transient solution with the low speed setting