*HEADING
: EIGENVALUE ANALYSIS OF AN UNCONSTRAINED PATCH OF ELEMENTS  [B21]
*NODE
*NGEN
*ELEMENT,TYPE=B21
*ELGEN,ELSET=ALL
*BEAM SECTION,SECTION=RECT,ELSET=ALL,MATERIAL=MAT
 0.1,0.1
*MATERIAL,NAME=MAT
*ELASTIC
 30E6,0.0
*DENSITY
7.5E-4,
*STEP,PERTURBATION
*FREQUENCY, eigensolver=lanczos, SIM=NO
9, , ,-1.E4
*NODE PRINT
 U,
*END STEP