Example 3 – Automatic inertia relief INREL,-2

In the final section of this example, the model is run using automatic inertia relief.  The input deck shown in Figure 3 is once again used except modified so that the SUPORT entry for automatic inertia relief is active.  Notice that when running automatic inertia relief there is no SUPORT entry.  The GRDPNT,0 entry simply requests that the Grid Point Weight Generator (GPWG) be included in the output file.  This GPWG assists in verification of results.  Note that PARAM,GRDPNT is still used in  PARAM,INREL,-2.  It defaults to the global origin, but can be (should be) defined near or at the CG.  Defining GRDPNT,0 just switches on the grid point weight generator and keeps the reference point at the (default) origin.

Figure 8: Classical analysis, Inertia Relief Example 3

Since the OLOAD results are calculated about the GRDPNT, and the GRDPNT is defined at the global origin for automatic inertia relief, the OLOAD table in the NASTRAN output file for this analysis is identical to that from the first analysis (due to the global origin coinciding with node 1). The NASTRAN output file for this analysis is shown in Figure 9. OLOAD results corresponding to the hand calculations in Figure 8 are circled in blue. Since automatic inertia relief does not use a SUPORT point, the NASTRAN output file does not include UIM 3035 (and therefore no strain energy or epsilon values).

Figure 9: NASTRAN results file for Example 3