PARAM, EXPERTNL

Bulk Data Entry Activates a nonlinear expert system to aid in the convergence of Nonlinear (static and transient) Analysis.

Parameter Values Description
EXPERTNL <YES, NO, AUTO, or CNTSTB>

Default = AUTO (For Small Displacement Analysis)

For both Small and Large Displacement Analysis, Contact Stabilization is inactive by default.

 PARAM,EXPERTNL has two functions embedded within it:
  • Automatic Time-stepping Schema (YES/AUTO/NO). This is applicable only for Small Displacement Nonlinear Analysis.
  • Contact Stabilization (CNTSTB). This is applicable to both Small and Large Displacement Analysis.
For Automatic Time-stepping Schema:
YES
Activates a nonlinear "expert system" that aids in the convergence of small displacement nonlinear problems. This version is designed to facilitate obtaining converged, high accuracy solutions without much concern for computational time. The system monitors the convergence of nonlinear processes and, if needed, implements measures designed to improve convergence for poorly converging cases. These measures include performing additional iterations, under-relaxation, automatic adjustment of the load increment, as well as backing off to the last convergent solution and retrying. This may lead to a large number of nonlinear iterations for poorly converging problems.
NO
Deactivates the nonlinear expert system.
AUTO
Activates a "light" version of the expert system, which is designed to facilitate converging nonlinear process in reasonably close to minimum number of iterations. In particular, this version may adjust the time step, including increasing the time step beyond that prescribed on the NLPARM card.
For Contact Stabilization:
CNTSTB
Additionally introduces temporary stabilization on contact interfaces (CONTACT or GAP(G) elements) that may improve nonlinear convergence, especially in cases where individual parts lack full support and are supported only by contact. The stabilization is applied only during incremental loading and is not present in the final solution for the respective nonlinear subcase. (Refer to the CNTSTB Bulk Data Entry for default and priority information).

Comments

  1. The interaction of PARAM, EXPERTNL, AUTO/YES with other nonlinear controls during a nonlinear (static and transient) analysis is summarized as:
    Option Controlled By Affected by EXPERTNL AUTO/YES
    DT, NINC NLPARM NO, these only control the initial increment size.
    MAXITER YES, MAXITER will be overridden by PARAM, EXPERTNL, AUTO/YES.
    MAXLS, LSTOL, TTERM NO

    PARAM, EXPERTNL, AUTO/YES does not affect any of the options in NLADAPT and TSTEP (in case of nonlinear transient analysis).