Modify the Step Definition

Change the load step to perform optimally with Helius PFA.

Many linear elastic analyses require only a single increment per step. A single increment is inadequate, however, when progressive failure is modeled because multiple increments are required to visualize the initiation and propagation of failure. Default nonlinear solution controls, as recommended in the Nonlinear Solution Control Parameters section of the Helius PFA User's Guide, are also modified.

1. Locate the SUBCASE 1 entry.
2. On the line below, type NLSTEP = 1.
3. Now locate the BEGIN BULK entry.
4. On the line below, type the following:

   $
   NLSTEP, 1, 1.0
    , GENERAL, 1000,
    , FIXED, 100,
    , MECH, PV, , 0.005
   $

Together, the entries from steps 2 and 4 define the nonlinear solution controls and time incrementation for the analysis.

• NLSTEP, 1, 1.0 specifies a total time of 1.0
• , GENERAL, 1000, specifies that the solver should perform up to 1000 iterations before evaluating the need to reduce the time incrementation. This allows MSC Nastran to take advantage of the enhanced convergence characteristics provided by Helius PFA.
• , FIXED, 100, specifies 100 increments should be used for the total solution time. This allows us to examine the progression of failure.
• , MECH, PV, , 0.005 specifies a force convergence tolerance of 0.5%. The default (10%) convergence tolerance is relatively loose and can result in unacceptable accuracy.

With these modifications, the bulk data file should appear as follows:

NASTRAN SYSTEM(444) = 1
NASTRAN SYSTEM(151) = 1
SOL 101
CEND
SUBCASE 1
   NLSTEP = 1
   SPC = 2001
   DISPLACEMENT(SORT1,REAL)=ALL
   SPCFORCES(SORT1,REAL)=ALL
   STRESS(SORT1,REAL,VONMISES,BILIN)=ALL
BEGIN BULK
$
NLSTEP, 1, 1.0
 , GENERAL, 1000,
 , FIXED, 100,
 , MECH, PV, , 0.005
$