*HEADING 
     Gas structure interaction with structure modeled using axisymmetric
     elements.

This test verifies the coupling between cavity fluid pressure and deformation 
of the structure enclosing the fluid cavity.
The deformation of the structure should change the fluid pressure according to
the fluid behavior definition and the pressure should get transferred to the 
structure.  
*PHYSICAL CONSTANTS, ABSOLUTE ZERO=-273.16, UNIVERSAL GAS CONSTANT=8.314
*NODE, NSET=NALL
1, 0, 0
2, 2, 0
3, 3, 0.5
4, 2, 1
5, 3, 1
6, 3, 2
7, 2, 2
8, 0, 2
*NODE, NSET=RIG_REF
9, 1, -1
*NODE, NSET=CAVREF
99, 0, 1
*NSET, NSET=FIX_BC
3, 4, 5
*NSET, NSET=DISP_BC
6, 7, 8
*ELEMENT, TYPE=SAX1, ELSET=SHELL
1, 7, 8
*ELEMENT, TYPE=CAX4R, ELSET=QUAD_SOLID
2, 7, 4, 5, 6
*ELEMENT, TYPE=CAX3, ELSET=TRI_SOLID
3, 4, 2, 3
*ELEMENT, TYPE=RAX2, ELSET=RIGID
4, 2, 1
*SURFACE, NAME=CAV_SURF, TYPE=ELEMENT
1, SPOS
2, S1
3, S1
4, SNEG
**
**Fluid cavity definition
**
*FLUID CAVITY, NAME=AXI_CAVITY, REF NODE=CAVREF, BEHAVIOR=AIR, 
SURFACE=CAV_SURF, AMBIENT PRESSURE=1.0E5

*FLUID BEHAVIOR, NAME=AIR
*MOLECULAR WEIGHT
0.0289
*CAPACITY, TYPE=POLYNOMIAL
28.110, 1.967E-3, 4.802E-6, -1.966E-9, 0.0
**
**Boundary conditions
**
*BOUNDARY
DISP_BC, 1, 2
7, 6, 6
8, 6, 6
FIX_BC, 1, 2
RIG_REF, 1, 2
RIG_REF, 6, 6
*ELSET, ELSET=SOLID
QUAD_SOLID, TRI_SOLID
**
**Section assignments
**
*SOLID SECTION, ELSET=SOLID, MATERIAL=MAT
*SHELL GENERAL SECTION, ELSET=SHELL, MATERIAL=MAT, OFFSET=SPOS
0.1
*RIGID BODY, REF NODE=RIG_REF, ELSET=RIGID, DENSITY=5000
0.1
**
**Material definitions
**
*MATERIAL, NAME=MAT
*DENSITY
5000
*ELASTIC
2E-10, 0.1
**
**Initial conditions
**
*INITIAL CONDITIONS, TYPE=TEMPERATURE
CAVREF, 20
*INITIAL CONDITIONS, TYPE=FLUID PRESSURE
CAVREF, 4.0E5
**
**Amplitude definition
**
*AMPLITUDE, NAME=RAMP
0, 0, 1, 1
*NSET, NSET=qa_testCAVREF
CAVREF
*NSET, NSET=qa_testRF2
7, 8, RIG_REF
*NSET, NSET=qa_testRF1
2, 4, 7
**
**Step 1: Apply displacement BC of 0.50 to all the nodes of a face with normal
**        in +2 direction.
**        cavity radius, r = 2; cavity depth, h =2
**        Initial CVOL = pi*(r*r)*h = 25.1327
**        CVOL at the end of step  = pi*(r*r)*(h + 0.5) = 31.4159
**        PCAV at the end of step = 3.0E5
**        Sum of RF2 on nodes of faces with normal in +2 or -2 direction
**                                                      = PCAV*pi*(r*r)
**        Sum of RF1 on nodes with normal in 1 direction 
**                                                     = PCAV*pi*(2*r)*(h+0.5)
**                                         
*STEP
*DYNAMIC, EXPLICIT, DIRECT USER CONTROL
0.001, 1
*BOUNDARY, OP=MOD, AMPLITUDE=RAMP
DISP_BC, 2, 2, 0.50
*OUTPUT, HISTORY, TIME INTERVAL=0.25
*NODE OUTPUT, NSET=qa_testCAVREF
PCAV, CVOL
*NODE OUTPUT, NSET=qa_testRF1
RF1
*NODE OUTPUT, NSET=qa_testRF2
RF2
*NODE OUTPUT, NSET=DISP_BC
U2
*END STEP
**
**Step 2: Apply displacement BC of -0.50 
**        All the parameters e.g. CVOL, PCAV, RF's at the end of this step 
**        will be the same as at the beginning of Step 1. 
**
*STEP
*DYNAMIC, EXPLICIT, DIRECT USER CONTROL
0.001, 1
*BOUNDARY, OP=MOD, AMPLITUDE=RAMP
DISP_BC, 2, 2, -0.50
*END STEP