contact analysis with friction, then adaptive descent is automatically turned on.The underlying contact
elements require adaptive descent for convergence.
Command(s):NROPT
GUI: Main Menu> Solution> Unabridged Menu> Analysis Type> Analysis Options
Valid only in a nonlinear analysis, this option specifies how often the tangent matrix is updated during
solution. The default behavior (NROPT,AUTO) allows the program to decide based on the kinds of
nonlinearities present in your model, and adaptive descent is activated automatically when appropriate.
The following additional options are available:
- Full (NROPT,FULL):
The program uses the full Newton-Raphson procedure, in which the stiffness matrix is updated at
every equilibrium iteration.If adaptive descent is on (optional), the program uses the tangent stiffness matrix only as long as the
iterations remain stable (that is, as long as the residual decreases, and no negative main diagonal
pivot occurs). If divergent trends are detected on an iteration, the program discards the divergent
iteration and restarts the solution, using a weighted combination of the secant and tangent stiffness
matrices. When the iterations return to a convergent pattern, the program resumes using the tangent
stiffness matrix. Activating adaptive descent usually enhances the program's ability to obtain converged
solutions for complicated nonlinear problems but is supported only for elements indicat ed under
"Special Features" in the Input Summary table (Table 4.n.1 for an element, where n is the element
number) in the Element Reference.- Modified (NROPT,MODI):
The program uses the modified Newton-Raphson technique, in which the tangent stiffness matrix is
updated at each substep. The matrix is not changed during equilibrium iterations at a substep. This
option is not applicable to large-deformation analyses. Adaptive descent is not available.- Initial Stiffness (NROPT,INIT ):
The program uses the initial stiffness matrix in every equilibrium iteration. This option can be less
likely to diverge than the full option, but it often requires more iterations to achieve convergence. It
is not applicable to large-deformation analyses. Adaptive descent is not available.- Full with unsymmetric matrix (NROPT,UNSYM):
The program uses the full Newton-Raphson procedure, in which the stiffness matrix is updated at
every equilibrium iteration. In addition, it generat es and uses unsymmetric matrices that you can use
for any of the following:- If you are running a pressure-driven collapse analysis, an unsymmetric pressure load stiffness might be
helpful in obtaining convergence. You can include pressure load stiffness using SOLCONTROL,INCP. - If you are defining an unsymmetric material model using TB,USER, you would need NROPT,UNSYM to
fully use the property you defined. - If you are running a contact analysis, an unsymmetric contact stiffness matrix would fully couple the
sliding and the normal stiffnesses. See Determining Contact Stiffness and Allowable Penetration in the
Contact Technology Guide for details.
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationNonlinear Structural Analysis