*HEADING
ECA4AFAS: 1D transient wave propagation in an acoustic medium with prescribed Acceleration on DOF 1. 
 ACAX4,ASI2A
 Verification problem: Transient Dynamics Tests
**
** C = root (K/rho)= 343.05 m/s   K=bulk mod, rho=density.  
**
*PREPRINT,ECHO=NO,HISTORY=NO,MODEL=YES
*NODE, Nset=ODB_NSET
    1, 0,
  101, 0, 1.,
  501, .5e-2,0.
  601, .5e-2,1.
 1001, 1.e-2,0.
 1101, 1.e-2,1.
*NGEN,NSET=CHANNEL
    1,101
 1001,1101
*NSET,NSET=SAMPLE,GENERATE
 1,101
*NSET,NSET=LOAD
 1,1001
*ELEMENT,TYPE=ACAX4
 1,1,1001,1002,2
*ELGEN,ELSET=CHANNEL
 1,100,1,
*SOLID SECTION,MATERIAL=AIR,ELSET=CHANNEL
 1.e-2, 
*surface, NAME=NRS
 100,S3
** Cr-sec is 1e-4 
** ASI element at x=0, so that acceleration may be prescribed
** directly:
*ELEMENT,TYPE=ASI2A,ELSET=LOAD
 1200,1,1001
*INTERFACE,ELSET=LOAD
 1.e-2,
*MATERIAL,NAME=AIR
*DENSITY
 1.21,
*ACOUSTIC MEDIUM,BULK MODULUS
 0.1424E6,
*RESTART,WRITE
*Elset,Elset=ODB_ESET
CHANNEL,
*Nset, Nset=ODB_NSET
ODB_NSET, CHANNEL, SAMPLE, LOAD
**
**
*STEP,INC=1000
*DYNAMIC,DIRECT
.0001,.0036
** Define nonreflective boundary at z=1
*IMPEDANCE
 100,I3
**
** Prescribe volume acceleration inwards
**   of  a0=1.
** Acceleration of interface element specified.
*BOUNDARY,TYPE=ACCELERATION
 LOAD,1,2,1.
**
*EL PRINT,FREQ=0
*NODE PRINT,NSET=SAMPLE,FREQ=6
 POR,
*NODE FILE,NSET=SAMPLE,FREQ=6
 POR,
*OUTPUT,FIELD,VARIABLE=PRESELECT,OP=ADD,FREQUENCY=9999
*OUTPUT,FIELD, OP=ADD,Frequency=6
*NODE OUTPUT,NSET=SAMPLE
 POR,
*OUTPUT,HISTORY,OP=ADD,Frequency=6
*NODE OUTPUT,NSET=SAMPLE
 POR,
*ENDSTEP
**
*STEP,INC=1000
*DYNAMIC,DIRECT
.0001,.0008
*IMPEDANCE,OP=NEW
*SIMPEDANCE
 NRS,
*BOUNDARY,TYPE=ACCELERATION
 LOAD,1,2,1.
*EL PRINT,FREQ=0
*NODE PRINT,NSET=SAMPLE,FREQ=6
 POR,
*NODE FILE,NSET=SAMPLE,FREQ=6
 POR,
*OUTPUT,FIELD,VARIABLE=PRESELECT,OP=ADD,FREQUENCY=9999
*OUTPUT,FIELD, OP=ADD,Frequency=6
*NODE OUTPUT,NSET=SAMPLE
 POR,
*OUTPUT,HISTORY,OP=ADD,Frequency=6
*NODE OUTPUT,NSET=SAMPLE
 POR,
*ENDSTEP