*parameter
neigenmodes = 20
*Heading
 S4R Elements
*Node
*Element, type=S4R
** Region: (Secn:Picked)
*Elset, elset=I1, generate
** Section: Secn
*Shell Section, elset=I1, material=Elas
0.5, 5
*Nset, nset=Set4
*Nset, nset=Set5
**
** MATERIALS
**
*Material, name=Elas
*Density
40
*Elastic
 1e+08,0.
** ----------------------------------------------------------------
**
** STEP: Stp1
**
*step
*frequency,eigen=lanc
<neigenmodes>,
*boundary
1,1,6
3,1,6
13,1,6
15,1,6
*node print
u,
*end step
*STEP
*substructure generate, type=z1, overwrite,
recovery matrix=yes, mass matrix=yes,
grav=yes,libr=lib_grav_shell3d
*RETAINED NODAL DOFS,sorted=no
*Retained Eigenmodes,generate
1,<neigenmodes>,1
*substructure matrix output, stiffness=yes,
mass=yes, grav=yes,recovery=yes, file=lib_grav_shell3d
*END STEP