*HEADING
Analysis of a 5 meter long pipe under tensile load
Pipe has OD of 180 mm and ID of 140 mm
S.I. Units
**
** Nodal coordinates
**
*NODE
1,0.
61, 5.0
*NGEN
1,61
**
** Element connectivity
**
*ELEMENT, TYPE=PIPE32
1, 1, 2, 3
*ELGEN, ELSET=PIPE
1, 30,2,1
**
*NSET, NSET=LEFT
1, 
*NSET, NSET=RIGHT
61, 
**
** Physical and material properties
**
*BEAM SECTION, ELSET=PIPE, MATERIAL=STEEL, SECTION=PIPE
0.09, 0.02
0.0, 0.0, -1.0
*MATERIAL, NAME=STEEL
*ELASTIC
200.E9, 0.3
*DENSITY
7800., 
**
** Step 1 - General step
**
*STEP, NLGEOM=YES
Apply axial tensile load of 4.0 MN
*STATIC
0.1, 1.0
*BOUNDARY
LEFT, 1, 6
RIGHT, 2, 6
*CLOAD
RIGHT, 1, 4.0E6
*ELSET, ELSET=ELEMENT25
25, 
*RESTART, WRITE, FREQUENCY=10
*OUTPUT, FIELD, FREQUENCY=10, VARIABLE=PRESELECT
*OUTPUT, HISTORY
*ELEMENT OUTPUT, ELSET=ELEMENT25
S, SINV
**********************************
** OUTPUT FOR ABAQUS QA PURPOSES
**********************************
*NODE FILE, FREQ=10
U, 
*EL FILE, FREQ=10
SINV, S
*END STEP
**
** Step 2 - Linear perturbation step
**
*STEP, PERTURBATION
Extract modes and frequencies
*FREQUENCY
8,
*RESTART, WRITE
*OUTPUT, FIELD, VARIABLE=PRESELECT
**********************************
** OUTPUT FOR ABAQUS QA PURPOSES
**********************************
*MODAL FILE
*END STEP

*HEADING
Increase tensile load on the piping system 
and determine lowest frequency.
*RESTART, READ
**
** Step 3 - General step
**
*STEP, NLGEOM=YES
Apply 8 MN axial tensile load
*STATIC
0.1, 1.
*CLOAD
RIGHT, 1, 8.0E6
*RESTART, WRITE, FREQUENCY=10
*OUTPUT, FIELD, FREQUENCY=10, VARIABLE=PRESELECT
*OUTPUT, HISTORY
*ELEMENT OUTPUT, ELSET=ELEMENT25
S, SINV
*END STEP
**
** Step 4 - Linear perturbation step
**
*STEP, PERTURBATION
Extract modes and frequencies
*FREQUENCY
8,
*RESTART, WRITE
*OUTPUT, FIELD, VARIABLE=PRESELECT
**********************************
** OUTPUT FOR ABAQUS QA PURPOSES
**********************************
*MODAL FILE
*END STEP