PRED

PRED, Sskey, --, Lskey
Activates a predictor in a nonlinear analysis.

Valid Products: Pro | Premium | Enterprise | PrepPost | Solver | AS add-on

Sskey

Substep predictor key:

AUTO

 — 

The program uses a predictor but, within certain exceptions, automatically switches prediction off. This behavior is the default; see "Command Default" for details.

OFF

 — 

No prediction occurs.

LINEAR (or ON)

 — 

Use the linear predictor on all substeps after the first.

QUADRATIC

 — 

Use the quadratic predictor on all substeps after the second.

--

Unused field.

Lskey

Load 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. (Sskey = ON is required.)

Command Default

The default command behavior is to use prediction (Sskey = AUTO). The AUTO option chooses to either use the linear predictor or to turn the predictor OFF. 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 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.

Notes

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. If the model has rotational degrees-of-freedom, the quadratic predictor could work more efficiently than the linear predictor.

This command is also valid in PREP7.

Menu Paths

Main Menu>Preprocessor>Loads>Analysis Type>Sol'n Controls>Nonlinear
Main Menu>Preprocessor>Loads>Load Step Opts>Nonlinear>Predictor
Main Menu>Solution>Analysis Type>Sol'n Controls>Nonlinear
Main Menu>Solution>Load Step Opts>Nonlinear>Predictor