A rigid object can be a set of elements for which all nodes are "fixed" (i.e., have non-zero b.c.). You can apply a displacement to the nodes (same for all nodes if translation). Feap also has some rigid body options. An object can be declared as rigid by inserting the command
RIGID n !
element list from: ELEM, BLOCk, BLENd, etc.
FLEX
deformable elements
There are limitations on mixing analysis types (especially the transient integrators).
User manual describes some of the options available.
If you have suggestions on what features are needed they can be added to possible future developments.
