*HEADING
: EIGENVALUE ANALYSIS OF AN UNCONSTRAINED PATCH OF ELEMENTS  [PIPE31H]
*NODE
 1,
 4,10.0
*NGEN
 1,4
*ELEMENT,TYPE=PIPE31H
 1, 1,2
*ELGEN,ELSET=ALL
 1,3,1,1
*BEAM SECTION,SECTION=PIPE,ELSET=ALL,MATERIAL=MAT
 0.1,0.01
*MATERIAL,NAME=MAT
*ELASTIC
 30E6,0.0
*DENSITY
7.5E-4, 
*STEP,PERTURBATION
*FREQUENCY, eigensolver=lanczos
10, , ,-100.0
*NODE PRINT
 U,
*OUTPUT,HISTORY,FREQUENCY=1
*MODAL OUTPUT
*END STEP