What is the difference between *CONTACT_AUTOMATIC_ SINGLE_SURFACE and *CONTACT_AUTOMATIC_GENERAL ?

Like *CONTACT_AUTOMATIC_SINGLE_SURFACE, *CONTACT_AUTOMATIC_GENERAL is a single surface contact, that is, the contact is defined wholly by the slave side. Both contact types consider shell thickness and beam thickness, that is, the contact surface is offset from the shell midplane and from the beam centerline. The beam cross section, for contact purposes only, is idealized as circular. At shell edges, the contact surface wraps around in a circular arc thus joining the contact surface on one side of the shell to the contact surface on the opposite side.

One important way in which an *CONTACT_AUTOMATIC_GENERAL contact differs from an *CONTACT_AUTOMATIC_SINGLE_SURFACE contact is the way in which beam contact and shell edge contact is handled. The *CONTACT_AUTOMATIC_GENERAL contact checks for penetration along the full length of beam elements, not just at the nodes of the beams. Similarly, *CONTACT_AUTOMATIC_GENERAL contact checks for penetration along the entire length of free (unshared) shell edges. By adding the option _INTERIOR to *CONTACT_AUTOMATIC_GENERAL in v. 960, edges of interior shells are also taken into account.

Another distinction is in the value of penetration that triggers release of the penetrating node from contact consideration (see Table 6.1 in the Keyword User's Manual). For *CONTACT_AUTOMATIC_GENERAL contact, that value is effectively unlimited whereas *CONTACT_AUTOMATIC_SINGLE_SURFACE contact will release the penetrating node after it penetrates approximately half an element thickness.

Yet another distinction is that, by default, *CONTACT_AUTOMATIC_GENERAL contact checks for nodal penetration through the three closest segments ("search depth" = 3) whereas *CONTACT_AUTOMATIC_SINGLE_SURFACE checks only two segments. The three segment check is more expensive but may be more robust for contact in corners. The default "search depth" for any automatic contact may be overridden on optional card A of *CONTACT_.

The segment-based alternate penalty formulation (invoked by setting SOFT = 2 on optional card A of *CONTACT_) is available for *CONTACT_AUTOMATIC_SINGLE_SURFACE but not for *CONTACT_AUTOMATIC_GENERAL. Setting SOFT=2 in an *CONTACT_AUTOMATIC_SINGLE_SURFACE contact changes the contact algorithm altogether. (See separate notes on SOFT=2 contact)

To write contact forces produced by any single surface contact to the RCFORC file, one must define a *CONTACT_FORCE_TRANSDUCER_PENALTY.

jpd 12/2002