OVCHECK, Method, Frequency, Set
Checks for overconstraint among constraint equations and
Lagrange multipliers.
MethodMethod used to determine which slave DOFs will be eliminated:
TOPO | — | Topological approach (default). This method only works with constraint equations; it does not work with Lagrange multipliers. |
ALGE | — | Algebraic approach. |
NONE | — | Do not use overconstraint detection logic. |
FrequencyFrequency of overconstraint detection for static or full transient analyses:
ITERATION | — | For all equilibrium iterations (default). |
SUBSTEP | — | At the beginning of each substep. |
LOADSTEP | — | At the beginning of each load step. |
SetSet of equations:
All | — | Check for overconstraint between all constraint equations (default). |
LAG | — | Check for overconstraint only on the set of equations that involves Lagrange multipliers. This is faster than checking all sets, especially when the model contains large MPC bonded contact pairs. |
Overconstraint detection is performed by using the topological approach among constraint equations only; the topological approach does not support Lagrange multipliers.
The OVCHECK command checks for overconstraint among the constraint equations (CE/CP) and the Lagrange multipliers for the globally assembled stiffness matrix. If overconstrained constraint equations or Lagrange multipliers are detected, they are automatically removed from the system of equations.
The constraint equations that are identified as redundant are removed from the system and printed to the output file. It is very important that you check the removed equations—they may lead to convergence issues, especially for nonlinear analyses.
The Frequency and Set arguments are active only for the topological method (Method = TOPO). If you do not issue the OVCHECK command, overconstraint detection is performed topologically, and
the slave DOFs are also determined topologically.
Overconstraint detection slows down the run. We recommend using it to validate that your model does not contain any overconstraints. Then, you can switch back to the default method (no OVCHECK command is needed).
As an example, consider the redundant set of constraint equations defined below:
CE,1, 1., 150,UX,1., 160,UX,-1. CE,2, 2., 150,UX,1., 160,UX,-1.
Equation number 2 will be removed by the overconstraint detection logic. However, this is an arbitrary decision since equation number 1 could be removed instead. This is an important choice as the constant term is not the same in these two constraint equations. Therefore, you must check the removed constraint equations carefully.
For detailed information on the topological and algebraic methods of overconstraint detection, see Constraints: Automatic Selection of Slave DOFs in the Mechanical APDL Theory Reference