ansys.mapdl.core.Mapdl.pred#

Mapdl.pred(sskey='', lskey='', **kwargs)#

Activates a predictor in a nonlinear analysis.

Mechanical APDL Command: PRED

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.

Parameters:
sskeystr

Substep predictor key:

  • AUTO - The program uses a predictor but, within certain exceptions, automatically switches prediction off. This behavior is the default; see PRED_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.

lskeystr

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.)

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.