Friction is not "incompatible" with the large rotation rod models. However, anytime you have non-linear restraints in the model, an iterative solution is necessary. Friction also makes a job non-linear.

The first thing to do with friction is to consider the discussion in the Technical Reference Manual on pages 6-16 and 6-17. The conclusion from this discussion is that once you put friction in a job, you can have multiple equilibrium solutions.

Typically, the place to start addressing friction convergence issues is in the configuration file. Try altering the FRICTION_STIFFNESS parameter. The default value of this parameter is 1e6 lb/in, try reducing this, try 500000, then 250000, then 100000, then 50000, until you achieve a stable, realistic solution. Try not to alter the other friction tolerances.

The problem with the SUStained case is that typically only weight (and pressure) is included. Therefore the load vector consists of loads in only the "Y" degree of freedom. If you don't have adequate horizontal restraint (friction doesn't count as "adequate" because you have to have movement to acquire friction forces), the model is unstable. This can also lead to unrealistic friction solutions.

Richard Ay (COADE, Inc.)
Richard Ay