*HEADING
 Tube with nonreflective end-condition and ASI elements. 
 Part of the air in the tube is modelled with truss elements
 with air properties.
**
********************
*RESTART,WRITE
********************
**
************************************************
**
**   Mesh Generation
**
*NODE, Nset=ODB_NSET
1, 
41,.5
*NGEN,NSET=NALL
1,41
*NSET,NSET=SAMPLE,GENERATE
1,41
*NSET,NSET=LOAD
1,
**
** First 5 elements are acoustic
*ELEMENT,TYPE=AC1D2
1,1,3
*ELGEN,ELSET=ACOU
1,5,2,1
**
** Then an ASI Element with normal to left
*ELEMENT,TYPE=ASI1, ELSET=ASILEFT
101,11
**
** Then 5 trusses
*ELEMENT,TYPE=T2D2
6,11,13
*ELGEN,ELSET=STRUCT
6,5,2,1
**
** Then an ASI Element with normal to right
*ELEMENT,TYPE=ASI1, ELSET=ASIRIGHT
102,21
**
** Next 10 elements are acoustic
*ELEMENT,TYPE=AC1D2
11,21,23
*ELGEN,ELSET=ACOU
11,10,2,1
**
*ELSET,ELSET=NONREF
20,
**
**
**
************************************************
**
**  Acoustic Element Properties
**
*SOLID SECTION,MATERIAL=AIR,ELSET=ACOU
1., 
**
*MATERIAL,NAME=AIR
*DENSITY
 1.21,
*ACOUSTIC MEDIUM,BULK MODULUS
 0.1424E6,
************************************************
**
**  Truss Element Properties
**
*SOLID SECTION,MATERIAL=AIRSOLID,ELSET=STRUCT
1., 
**
*MATERIAL,NAME=AIRSOLID
*DENSITY
 1.21,
*ELASTIC
 0.1424E6,
************************************************
**
**  ASI Element Properties
**
*INTERFACE,ELSET=ASILEFT
      1,    -1,0,0
**thick,    normal
*INTERFACE,ELSET=ASIRIGHT
      1,     1,0,0
**thick,    normal
**
************************************************
**
**
**  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
**
** 
**
*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
**
************************************************  
**
** Sets added by addodb
**
*Elset,Elset=ODB_ESET
ACOU, STRUCT
**
**
*Nset, Nset=ODB_NSET
ODB_NSET, NALL, SAMPLE, LOAD
**
**
*STEP
*STEADY STATE DYNAMIC,DIRECT
100,
*IMPEDANCE
 NONREF,I2
**
** 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
LOAD, 8, 1.
*NODE PRINT, NSET=SAMPLE
COORD,POR,PPOR
*OUTPUT,FIELD
*NODE OUTPUT,NSET=SAMPLE
POR,
*OUTPUT,HISTORY
*NODE OUTPUT,NSET=SAMPLE
POR,
*END STEP
**
**
*STEP
*FREQUENCY,EIGENSOLVER=LANCZOS,NORMALIZATION=MASS
29,,,-10.
*NODE PRINT,F=0
*EL PRINT,F=0
*OUTPUT,FIELD,Frequency=0
*END STEP
**
**
*STEP
*STEADY STATE DYNAMIC,SUBSPACE PROJECTION
100,
*IMPEDANCE
 NONREF,I2
**
** 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
LOAD, 8, 1.
*NODE PRINT, NSET=SAMPLE
COORD,POR,PPOR
*OUTPUT,FIELD
*NODE OUTPUT,NSET=SAMPLE
POR,
*OUTPUT,HISTORY
*NODE OUTPUT,NSET=SAMPLE
POR,
*END STEP