*HEADING
: EIGENVALUE ANALYSIS OF AN UNCONSTRAINED PATCH OF ELEMENTS  [B31OS]
*NODE
 1,
 4,10.0
*NGEN
 1,4
*ELEMENT,TYPE=B31OS
 1, 1,2
*ELGEN,ELSET=ALL
 1,3,1,1
*BEAM SECTION,SECTION=I,ELSET=ALL,MATERIAL=MAT
 5.,10.,10.,10.,1.,1.,1.
*MATERIAL,NAME=MAT
*ELASTIC
 30E6,0.0
*DENSITY
7.5E-4, 
*STEP,PERTURBATION
*FREQUENCY, eigensolver=lanczos, SIM=NO
9, , ,-1.0E4
*NODE PRINT
 U,
*END STEP