New Contact Solution Options in ADINA — the MNO and Gap-override Options
There are two new important features for contact analysis in ADINA that we want to briefly illustrate here. These are the gap-override option and the materially-nonlinear-only (MNO) analysis option.
In the MNO analysis option, the contact solution is performed with no geometric nonlinearities in the contact search and in the enforcement of the contact conditions — the nonlinearity is only due to enforcing the contact conditions (assuming infinitesimal displacements) and possible frictional sliding. Hence, in essence, only material nonlinearities along the contact surface are accounted for. This option is used appropriately if the displacements on the contact surfaces are not large, and can result in significantly fewer iterations for solution of the problem.
The gap-override option is designed to obtain accurate solutions when the contact surfaces are curved. The
figure below shows schematically how two meshes representing curved geometries are coming into contact. Since
the curved contact lines are idealized by straight lines, the geometric contact gap measured using the discretization
of the structures is in error. In the gap-override option, ADINA replaces, using a user-specified gap-override
value, the gaps and penetrations calculated from the finite element meshes. This feature is useful when the gap
error resulting from the mesh discretization is comparable to, or larger than, the true gap, as frequently encountered
with non-matching meshes.
The following figures illustrate the two new options. The figure on the right shows the finite element mesh used for the contact
analysis, and the next figures show the results obtained using the gap-override option. Here the initial gap is
set to be zero. We see that smooth contact tractions are predicted using the standard contact algorithm (in which
geometric nonlinearities are included) and the MNO contact algorithm. The peak tractions are larger when using the MNO option
because the displacements on the contact surfaces are not very small. Therefore, it is more appropriate to use in this analysis the
standard contact solution algorithm.