*HEADING
 AIRSPRING -- AXISYMMETRIC MODEL
*NODE
*NODE, NSET = RIGID
*NSET, NSET = CAVITY
*NGEN, LINE = C
**
** RUBBER SPRING
**
*ELEMENT, TYPE = SAX1, ELSET = SPRING
*ELGEN, ELSET = SPRING
*SHELL SECTION, COMPOSITE, ELSET = SPRING
2.5E-3, 3, RUBBER
1.0E-3, 3, STEEL
2.5E-3, 3, RUBBER
*MATERIAL, NAME = RUBBER
*HYPERELASTIC, POLYNOMIAL, N = 1
3.2E6, 0.8E6
*DENSITY
1000.,
*MATERIAL, NAME = STEEL
*ELASTIC, TYPE=LAMINA
2.48E9, 2.86E7, 9.105, 8.0E6, 8.0E6, 8.0E6
**
** RIGID BODY/SURFACE
**
*NODE,NSET=RIGNODE
*NGEN,NSET=RIGNODE,LINE=C
*ELEMENT,TYPE=RAX2,ELSET=RIGELEM
*ELGEN,ELSET=RIGELEM
*RIGID BODY, REF NODE=1000, ELSET=RIGELEM
**
** FLUID CAVITY
**
*ELEMENT, TYPE = SAX1, ELSET = FLUID
*SHELL SECTION, ELSET=FLUID, MATERIAL=A1
1E-3,
*MATERIAL,NAME=A1
*ELASTIC
1E5, 0.1
*SURFACE, TYPE=ELEMENT, NAME=CAVSURF
 SPRING, SPOS
 FLUID, SPOS
*PHYSICAL CONSTANTS, ABSOLUTE ZERO=-273.16, UNIVERSAL GAS CONSTANT=8.314
*FLUID CAVITY, NAME=SPRINGCAV, BEHAVIOR=GAS, REF NODE=500, SURFACE=CAVSURF, AMBIENT PRESSURE=101.36E+3
*FLUID BEHAVIOR, NAME=GAS
*MOLECULAR WEIGHT
**
*BOUNDARY
1,1,2
4,1,2
4,6,6
6,1,1
RIGID,1,2
RIGID,6,6
*NSET,NSET=RIG
*SURFACE,TYPE=ELEMENT,NAME=ASURF
ECON,SNEG
*SURFACE,TYPE=ELEMENT,NAME=BSURF
RIGELEM,SNEG
**
** CONTACT DEFINITION
**
*ELSET,ELSET=ECON,GENERATE
*CONTACT PAIR,INTERACTION=SMOOTH,TYPE=SURFACE,NOTHICK
ASURF,BSURF
*SURFACE INTERACTION,NAME=SMOOTH
*SURFACE BEHAVIOR,PENALTY
,,1.e3
*********** HISTORY DEFINITION ******************
**
** STEP 1 - INFLATION STEP (5 ATMOSPHERES)
**
*STEP, NLGEOM
*STATIC
0.025,1.0
*MONITOR, NODE=26, DOF=1
*BOUNDARY
CAVITY,8,8, 5.066E5
*OUTPUT,FIELD,VARIABLE=PRESELECT
*NODE OUTPUT
U,RF
CF,
*ELEMENT OUTPUT
S,
*CONTACT OUTPUT,VARIABLE=PRESELECT,SLAVE=ASURF
*OUTPUT,HISTORY
*NODE OUTPUT,NSET=CAVITY
PCAV,CVOL
*NODE OUTPUT, NSET=RIGID
U, RF
CF,
*END STEP
**
** STEP 2 - SEAL CAVITY, RELEASE GRIP ON
**          RIGID SURFACE,
**          AND LOAD RIGID SURFACE
**
*STEP, NLGEOM
*STATIC
1.0, 1.0
*MONITOR, NODE=1000, DOF=2
*BOUNDARY, OP=NEW
1,1,2
4,1,2
4,6,6
6,1,1
RIGID,1
RIGID,6
*CLOAD
RIGID,2,-150.E3
*END STEP
**
** STEP 3 - PERTURBATION STEP
**          2 LOAD CASES
*STEP, PERTURBATION
*STATIC
*BOUNDARY, OP=NEW
1,1,2
4,1,2
4,6,6
6,1,1
RIGID,1
RIGID,6
** LOAD CASE 1
** UNIT AXIAL DISPLACEMENT WITH CAVITY PRESSURE FREE
*LOAD CASE, NAME="PRESSURE FREE"
*BOUNDARY, OP=NEW
RIGID, 2, 2, 1.E-3
*END LOAD CASE
** LOAD CASE 2
** UNIT LOAD WITH CAVITY PRESS FIXED
*LOAD CASE, NAME="PRESSURE FIXED"
*BOUNDARY, OP=NEW
CAVITY, 8, 8, 0
RIGID,  2, 2, 1.E-3
*END LOAD CASE
*END STEP
**
** STEP 4 - NONLINEAR LOAD DEFLECTION CURVE
**
*STEP, NLGEOM
*STATIC
0.1,1.0
*CLOAD
RIGID,2,-240.E3
*END STEP