Mechanical APDL Structural Analysis Guide

After you have created a model, set solution controls (analysis type, analysis options, load step options,
and so on), apply loads, and solve. A nonlinear solution differs from a linear solution in that it often
requires multiple load increments, and always requires equilibrium iterations. The general procedure
for performing these tasks follows. See Example Nonlinear Analysis (GUI Method) (p. 273) for an example
problem that walks you through a specific nonlinear analysis.

8.6.2. Set Solution Controls

Setting solution controls for a nonlinear analysis involves the same options and method of access (the
Solution Controls dialog box) as those used for a linear structural static analysis. For a nonlinear analysis,
the default settings in the Solution Controls dialog box are essentially the same settings employed by
the automatic solution control method described in Running a Nonlinear Analysis (p. 242). See the fol-
lowing sections in Structural Static Analysis (p. 9), with exceptions noted:

• Set Solution Controls (p. 10)


• Access the Solution Controls Dialog Box (p. 11)


• Using the Basic Tab (p. 11)


• The Transient Tab (p. 12)


• Using the Sol'n Options Tab (p. 12)


• Using the Nonlinear Tab (p. 12)


• Using the Advanced NL Tab (p. 13)

8.6.2.1. Using the Basic Tab: Special Considerations

Special considerations for setting these options in a nonlinear structural static analysis include:

• When setting ANTYPE and NLGEOM, choose Large Displacement Static if you are performing a
  new analysis. (Not all nonlinear analyses produce large deformations, however. See Using Geometric
  Nonlinearities (p. 200) for a further discussion of large deformations.) Choose Restart Current Analysis
  if you want to restart a failed nonlinear analysis. You cannot change this setting after the first load
  step (that is, after you issue your first SOLVE command). Typically, you perform a new analysis, rather
  than a restart. (Restarts are discussed in the Basic Analysis Guide.)


• When working with time settings, remember that these options can be changed at any load step.
  See Loading in the Basic Analysis Guide for more information about these options. Advanced
  time/frequency options, in addition to those available on the Solution Controls dialog box, are discussed
  in Advanced Load Step Options You Can Set on the Solution Controls Dialog Box (p. 244).

A nonlinear analysis requires multiple substeps (or time steps; the two terms are equivalent)

within each load step so that the program can apply the specified loads gradually and obtain

an accurat e solution.The NSUBST and DELTIM commands both achieve the same effect (estab-

lishing a load step's starting, minimum, and maximum step size), but by reciprocal means.NSUBST

defines the number of substeps to be taken within a load step, whereas DELTIM defines the

time step size explicitly. If automatic time stepping is off (AUTOTS), then the starting substep

size is used throughout the load step.

• OUTRES controls the data on the results file (Jobname.RST). By default, only the last substep is
  written to the results file in a nonlinear analysis.

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Performing a Nonlinear Static Analysis