MSC Nastran (since 2011) has included an option for a static iterative solver. If the user is comfortable using iterative methods use CASI.
Run times on large models are significantly reduced when the card
SMETHOD = ELEMENT
is included in the Nastran .bdf file case control section.
MSC comparison chart:
ESA’s NASTRAN_Settings.txt template located here includes an example the CASI iterative solver card.
The approach is recommended to use for quick debug of models (faster than running modal) but not recommended for final result runs.
A quick comparison using CASI and the default (direct solver) for pressure runs (reactions should be zero as possible). The iterative solver has a default tolerance of (1E-6). A slight decrease in solve time is achieved if the tolerance is increased to 1E-3.
For 3D element dominated models debug runs can be accomplished in half the time.
Note that the default solver should be used for final runs.