PRED, Sskey, --, Lskey
Activates a predictor in a nonlinear analysis.
SskeySubstep predictor key:
OFF | — | No prediction occurs. |
ON | — | Use a predictor on all substeps after the first. |
AUTO | — | The program uses a predictor but, within certain exceptions, automatically switches prediction off. This behavior is the default; see "Command Default" for details. |
--Unused field.
LskeyLoad step predictor:
OFF | — | No prediction across load steps occurs. This is the default behavior. |
ON | — | Use a predictor also on the first substep
of the load step. ( |
The default command behavior is to use prediction (Sskey = AUTO). However, prediction does not occur if
one or more of these conditions exist:
Over prediction occurs due to a large residual force or excessive element distortion.
You are using the SOLID65 element.
You are mapping (MAPSOLVE) variables to a new mesh during rezoning. (Prediction does not occur for any MAPSOLVE substeps, nor for the first substep afterwards.)
You have steady-state analysis defined (SSTATE) and contact elements exist in the model.
Activates a predictor in a nonlinear analysis on the degree-of-freedom solution for the first equilibrium iteration of each substep.
When using the arc-length method (ARCLEN, ARCTRM), you cannot issue the DOF solution predictor command (PRED), the automatic time stepping command (AUTOTS), or the line search command (LNSRCH). If you activate the arc-length method after you set PRED, AUTOTS, or LNSRCH, a warning message appears. If you elect to proceed with the arc-length method, the program disables your DOF predictor, automatic time stepping, and line search settings, and the time step size is controlled by the arc-length method internally.
When using step-applied loads, such as TUNIF, BFUNIF, etc., or other types of non-monotonic loads, the predictor may adversely affect the convergence. If the solution is discontinuous, the predictor may need to be turned off.
When performing a nonlinear analysis involving large rotations, the predictor may require using smaller substeps.
This command is also valid in PREP7.