*HEADING
 EC38AFAI: AC3D20 ELEMENTS
 Tube with nonreflective end-condition and ASI elements. 
 Part of the air in the tube is modelled with continuum elements
 with air properties.
**
********************
*RESTART,WRITE
********************
*NODE, Nset=ODB_NSET
1, 
41,.5
101,,0.0125
141,0.5,0.0125
201,,0.025
241,0.5,0.025
*NGEN,NSET=NBACK
1,41
101,141
201,241
*NCOPY,CHANGE NUMBER=300, OLD SET=NBACK, NEW SET=NMID,SHIFT
0.0,0.0,0.0125

*NCOPY,CHANGE NUMBER=600, OLD SET=NBACK, NEW SET=NFRONT,SHIFT
0.0,0.0,0.025

*NSET,NSET=NALL
NBACK,NFRONT,NMID
*NSET,NSET=SAMPLE,GEN
1,41
*NSET,NSET=LOAD1
1,201,801,601
*NSET,NSET=LOAD2
101,501,701,301
**
** First 5 elements are acoustic
*ELEMENT,TYPE=AC3D20
1,1,601,603,3,201,801,803,203,301,602,303,2,501,
802,503,202,101,701,703,103
*ELGEN,ELSET=ACOU
1,5,2,1
**
** Then an ASI Element with normal to left
*ELEMENT,TYPE=ASI8, ELSET=ASILEFT
101,11,611,811,211,311,711,511,111
**
** Then 5 continuum elements
*ELEMENT,TYPE=C3D20
6,11,611,613,13,211,811,813,213,311,612,313,12,
511,812,513,212,111,711,713,113
*ELGEN,ELSET=STRUCT
6,5,2,1
**
** Then an ASI Element with normal to right
*ELEMENT,TYPE=ASI8, ELSET=ASIRIGHT
102,21,221,821,621,121,521,721,321
**
** Next 10 elements are acoustic
*ELEMENT,TYPE=AC3D20
11,21,621,623,23,221,821,823,223,321,622,323,22,
521,822,523,222,121,721,723,123
*ELGEN,ELSET=ACOU
11,10,2,1
**
*ELSET,ELSET=NONREF
20,
************************************************
**
**  Acoustic Element Properties
**
*SOLID SECTION,MATERIAL=AIR,ELSET=ACOU
*MATERIAL,NAME=AIR
*DENSITY
 1.21,
*ACOUSTIC MEDIUM,BULK MODULUS
 0.1424E6,
************************************************
**
**  Continuum Element Properties
**
*SOLID SECTION,MATERIAL=AIRSOLID,ELSET=STRUCT
*MATERIAL,NAME=AIRSOLID
*DENSITY
 1.21,
*ELASTIC
 0.1424E6,
************************************************
**
**  ASI Element Properties
**
*INTERFACE,ELSET=ASILEFT
*INTERFACE,ELSET=ASIRIGHT
**
************************************************
*AMPLITUDE,NAME=OMEGA
0.,0., 1E6,6.2831853E6
************************************************
**       ** ANALYTIC SOLUTION  **
**  
**  at freq=100,
**  Impedance: Z = root( K_f rho )
**               = 415.09
**  Propagation constant 
**             b = i (omega/K_f) Z
**               = 1.8315  i
**
**  Solution: with nonreflective end,
**  Complex pressure
**             p(x) = Z v(0) exp( - b x)
**  i.e. |p(x)| = |Z v(0)| exp ( - Re(b) x)
**              =  415.09 
**
**       Arg(p) = Arg(Z) - Im(b) x
**       ppor   = - 104.94 x
**
************************************************  
*Elset,Elset=ODB_ESET
ACOU, STRUCT
**
**
*Nset, Nset=ODB_NSET
ODB_NSET, NBACK, NMID, NFRONT
NALL, SAMPLE, LOAD1, LOAD2
**
**
*STEP
*STEADY STATE DYNAMIC,DIRECT
100,
**  For reference, these IMPEDANCE PROPERTY
**  constants could be used to specify the nonreflecting 
**  condition at the given frequency:
**  1/k1= 0, 1/c1= 2.40908E-03
**        0,       1/Z
**
*IMPEDANCE
 NONREF,I5
**
** Conditions at x=0 : Define the source inward accel
** to be  a =  omega i, so v (inward) = 1.
** The loaded node has a tributary area of 1.
**
*CLOAD,LOAD CASE=2, AMP=OMEGA
LOAD1, 8,  2.6041667E-05
LOAD2, 8,  1.3020833E-04
** simulation of uniaxial condition
*BOUNDARY
NALL,2,3
*NODE PRINT, NSET=SAMPLE
COORD,POR,PPOR
*OUTPUT,FIELD
*NODE OUTPUT,NSET=nall
POR,
*ELEMENT OUTPUT,ELSET=ACOU
INTEN,acv,gradp
*ELEMENTOUTPUT,ELSET=STRUCT
INTEN,S
*OUTPUT,HISTORY
*NODE OUTPUT,NSET=nall
POR,U
*END STEP