Parameter

Values

Description

EXPERTNL

<YES, NO, CNTSTB, or AUTO>

Default = AUTO

YES activates a nonlinear "expert system" that aids in the convergence of small displacement nonlinear problems (NLSTAT). 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.

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).

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.

This parameter does not apply to geometric nonlinear solution sequences (EXPDYN).