8.6.2.3.6. Line Search Option.
Automatic solution control toggles line search on and off as needed. For most contact problems,LNSRCH
is toggled on. For most non-contact problems,LNSRCH is toggled off.
This convergence-enhancement tool multiplies the calculated displacement increment by a program-
calculated scale factor (having a value between 0 and 1), whenever a stiffening response is detected.
Because the line search algorithm is intended to be an alternative to the adaptive descent option
(NROPT), adaptive descent is not automatically activated if the line search option is on.We do not re-
commend activating both line search and adaptive descent simultaneously.
When an imposed displacement exists, a run cannot converge until at least one of the iterations has a
line search value of 1. The program scales the entire ∆U vector, including the imposed displacement
value; otherwise, a "small" displacement occurs everywhere except at the imposed degree of freedom.
Until one of the iterations has a line search value of 1, the program does not impose the full value of
the displacement.
8.6.2.3.7. Cutback Criteria
For finer control over bisections and cutback in time step size, use (CUTCONTROL,Lab,VALUE,Option).
By default, for Lab = PLSLIMIT (maximum plastic strain increment limit),VALUE is set to 15%.This field
is set to such a large value for avoiding unnecessary bisections caused by high plastic strain due to a
local singularity which is not normally of interest to the user. For explicit creep (Option = 0),Lab =
CRPLIM (creep increment limit) and VALUE is set to 10%.This is a reasonable limit for creep analysis.
For implicit creep (Option = 1), there is no maximum creep criteria by default.You can however,
specify any creep ratio control. The number of points per cycle for second order dynamic equations
(Lab = NPOINT ) is set to VALUE = 13 by default to gain efficiency at little cost to accuracy.
8.6.3. Set Additional Solution Options.
This section discusses additional options that you can set for the solution.These options do not appear
on the Solution Controls dialog box because they are used infrequently, and their default settings rarely
need to be changed. Menu paths are provided in this section to help you access these options for those
cases in which you choose to override the program-assigned defaults.
8.6.3.1. Advanced Analysis Options You Cannot Set via the Solution Controls Dialog Box
The following sections describe some advanced analysis options that you can set for your analysis. You
cannot use the Solution Controls dialog box to set these options. Instead, set them using the standard
set of solution commands and the standard corresponding menu paths.
8.6.3.1.1. Stress Stiffness
8.6.3.1.2. Newton-Raphson Option.
8.6.3.1.1. Stress Stiffness
To account for buckling, bifurcation behavior, the program includes stress stiffness in all geometrically
nonlinear analyses (NLGEOM,ON).
8.6.3.1.2. Newton-Raphson Option
Automatic solution control uses the FULL Newton-Raphson option with adaptive descent off if there is
a nonlinearity present. However, when node-to-node, node-to-surface contact elements are used for
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationPerforming a Nonlinear Static Analysis