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[FAQ]

IGNORE = 0 is the default option in contacts with SOFT = 0 or 1. When IGNORE = 0, if an initial penetration is detected, the contact algorithm will move the penetrating node outwards to eliminate the initial penetration. This will perturb the initial geometry, but it will not apply contact forces at time 0. When IGNORE = 1, the initial penetration (d0) is stored as the reference penetration. At each time step, if the current penetration (d) is greater than the reference penetration, the contact force (F) corresponds to the current minus the reference penetration based on the relation F = k * (d – d0) where k is the penalty stiffness. If the current penetration is less than the reference penetration, the reference penetration is updated to the current penetration and no contact force is developed. IGNORE = 2 is the same as IGNORE = 1 but prints warning messages for the penetrations. SOFT = 2 contact is implemented with IGNORE = 1 and also supports IGNORE = 2 to report the initial penetrations. In MORTAR contacts, IGNORE = 2 is the default option, but it has a different meaning from the other contacts. For this option, the initial penetrations are not tracked, but the contact surface is fixed at its initial location. By default, the initial penetrations are given zero contact pressure. An initial contact pressure can be imposed on the interface by setting MPAR1 to the desired contact pressure, when IGNORE = 2. In MORTAR contacts, IGNORE can be also set equal to 3 or 4. For details on these options please see the remark “Overview of Mortar Contact” in Manual Vol I.