Create an Analysis Step with a Text Editor

Define a step with the proper time incrementation and nonlinear solution controls that best allow Helius PFA to reach a converged solution.

We have already defined our model geometry and are now ready to create a load step. Many linear elastic analyses require only a single increment per step. However, a single increment is inadequate for simulations of progressive failure. With the Nastran input file (.nas) still open in a text editor:

1. Locate the SUBCASE entry.
2. Below the SUBCASE entry, add the following line:

      NLPARM = 1

3. Now locate the BEGIN BULK entry. Below this, add the following lines:

   NLPARM         1     100            ITER       1    1000             ALL+       
   +                                   1000                                +       
   +

Together, these 3 lines define the set of nonlinear parameters to use for the analysis. The NLPARM we defined uses 100 increments over a total time of 1.0. We have also requested that 1000 equilibrium iterations be performed before the code evaluates the need to reduce the time incrementation. This allows Autodesk Nastran to take advantage of the improved convergence characteristics provided by Helius PFA. We also used the NLSTEP entry to modify the default force convergence tolerance.

For additional details on the NLPARM entry as it pertains to Helius PFA, refer to the Nonlinear Solution Control Parameters.

The input file should now appear similar to what is shown below:

SUBCASE 1
  TITLE = Nonlinear Static Analysis
  ECHO = NONE
  DISPLACEMENT(PLOT) = ALL
  SPCFORCE(PLOT) = ALL
  NLSTRESS(PLOT) = ALL
  STRESS(PLOT,CORNER) = ALL 
  ELSTRAIN(GAUSS) = ALL 
  ELSTRESS(GAUSS) = ALL
  SPC = 2001
  NLPARM = 1
$
BEGIN BULK
$
PARAM,UNITS,IN-LBF-BTU-SEC
PARAM,LGDISP,0
PARAM,OGEOM,NO
PARAM,AUTOSPC,YES
PARAM,GRDPNT,0 
PARAM,NLTOL,2 
PARAM,SOLUTIONERROR,OFF
PARAM,HEXINODE,OFF
PARAM,HEXREDORD,OFF
NLPARM         1     100            ITER       1    1000             ALL+       
+                                   1000                                +       
+
$

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