CNTNLSUB

Subcase Information Entry

CNTNLSUB – Continue nonlinear solution sequence from a preceding nonlinear subcase

Description

The CNTNLSUB command can be used in the Subcase Information section to continue a nonlinear solution from a preceding nonlinear subcase, and thus create complex loading sequences.

Format

CNTNLSUB = option

Argument	Options	Description
option	<Yes, No, SID> Defaults: If CNTNLSUB does not exist in the input file, the default is No. If CNTNLSUB exists in the input file, but a value is not specified, the default is Yes.	Yes:	This nonlinear subcase continues the nonlinear solution from the nonlinear subcase immediately preceding it. "Preceding" refers to the sequence of subcases in the deck, and not the subcase numbering. If CNTNLSUB,YES is used within a subcase, the preceding subcase must be nonlinear subcase of the same type. If CNTNLSUB,YES is used above the first subcase, then all the consecutive nonlinear subcases of the same type will continue each other (however, other types of subcases interspersed between nonlinear ones will “break” the continuation sequence).
		No:	This nonlinear subcase executes a new solution sequence starting from the initial, stress-free state of the model. See comment 1.
		SID: Subcase ID	This nonlinear subcase continues the nonlinear solution from SUBCASE SID. SUBCASE SID must precede the current subcase in the deck and must be a nonlinear subcase of the same type. See comment 1.

Comments

1.	This command applies only to nonlinear subcases.

Nonlinear subcases may only be continued from other nonlinear subcases of the same analysis type. That is, Small Displacement Nonlinear Analysis subcases (ANALYSIS=NLSTAT) may only be continued from other Small Displacement Nonlinear Analysis subcases, Nonlinear Transient Dynamics Subcases (ANALYSIS=EXPDYN) may only be continued from other Nonlinear Transient Dynamics Subcases, and Large Displacement Nonlinear Analysis Subcases (PARAM, LGDISP, 1) may only be continued from other Large Displacement Nonlinear Analysis Subcases.

2.	Only one CNTNLSUB entry can be defined for each subcase.

3.	If CNTNLSUB = option is present above the first subcase, it is applied to all nonlinear subcases. (CNTNLSUB = SID is only allowed within a subcase).

CNTNLSUB is mostly relevant in path-dependent problems, such as plasticity or gap/contact analysis with friction/stick. In these problems, subcase continuation can be used to create complex loading paths that will typically produce very different results than simple proportional loading of a single subcase. CNTNLSUB also affects the convergence history and, to some extent, the results in problems that typically are not path-dependent, such as gap/contact analysis without friction.

If displacement boundary conditions specified by non-zero SPC or SPCD’s which exist in preceding subcase (say, Subcase 1) are removed in the subsequent nonlinear subcase (say, Subcase 2), then the SPC force resulting from non-zero SPC or SPCD in Subcase 1 would be gradually ramped down to zero in Subcase 2.

6. If the deformed shape resulting from the preceding subcase requires to be unchanged in Subcase 2, then the D field should be set to “F” on the SPC or SPCD entries.