You should first try NROPT,FULL, then try NROPT,UNSYM if you experience convergence difficulties.
(Using an unsymmetric solver requires more computational time to obtain a solution than if you use
a symmetric solver.)If a multistatus element is in the model, it is updated at the iteration in which it changes status, irre-
spective of the Newton-Raphson option.
8.6.3.2. Advanced Load Step Options.
The following sections describe some advanced load step options that you can set for your analysis.
You cannot use the Solution Controls dialog box to set the options described below. Instead, set them
using the standard set of solution commands and the standard corresponding menu paths.
8.6.3.2.1. Creep Criteria
8.6.3.2.2. Time Step Open Control
8.6.3.2.3. Solution Monitoring
8.6.3.2.4. Birth and Death
8.6.3.2.5. Output Control8.6.3.2.1. Creep Criteria
If your structure exhibits creep behavior, you can specify a creep criterion for automatic time step ad-
justment (CRPLIM,CRCR,Option). (If automatic time stepping (AUTOTS) is off, this creep criterion has
no effect.) The program computes the ratio of creep strain increment (∆εcr, the change in creep strain
in the last time step) to the elastic strain (εel), for all elements. If the maximum ratio is greater than the
criterion CRCR, the program then decreases the next time step size; if it is less, the program might in-
crease the next time step size. ( The program also bases automatic time stepping on the number of
equilibrium iterations, impending element status change, and plastic strain increment. The time step
size is adjusted to the minimum size calculated for any of these items.) For explicit creep (Option =
0), if the ratio ∆εcr / εel is above the stability limit of 0.25, and if the time increment cannot be decreased,
a divergent solution is possible and the analysis terminates with an error message. This problem is
avoidable by making the minimum time step size sufficiently small (DELTIM and NSUBST). For implicit
creep (Option = 1), there is no maximum creep limit by default.You can however, specify any creep
ra tio control.
Command(s):CRPLIM
GUI: Main Menu> Solution> Unabridged Menu> Load Step Opts> Nonlinear> Creep Criterion
If you do not want to include the effects of creep in your analysis, use the RATE command with Option
= OFF, or set the time steps to be longer than the previous time step, but not more than 1.0e-6 longer.
8.6.3.2.2. Time Step Open Control
This option is available for thermal analysis. (Remember that you cannot perform a thermal analysis
using the Solution Controls dialog box; you must use the standard set of solution commands or the
standard corresponding menu paths instead.) This option's primary use is in unsteady state thermal
analysis where the final temperature stage reaches a steady state. In such cases, the time step can be
opened quickly. The default is that if the TEMP increment is smaller than 0.1 in three (NUMSTEP = 3)
contiguous substeps, the time step size can be "opened-up" (value = 0.1 by default).The time step size
can then be opened continuously for greater solution efficiency.
Command(s):OPNCONTROL
GUI: Main Menu> Solution> Unabridged Menu> Load Step Opts> Nonlinear> Open Control
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationPerforming a Nonlinear Static Analysis