*HEADING
EC24AFAS: 1D transient wave propagation in an acoustic medium with prescribed Acceleration on DOF 1. AC2D4,ASI2
 Verification problem: Transient Dynamics Tests
**
** C = root (K/rho)= 343.05 m/s   K=bulk mod, rho=density.  
**
** Analytic solution to prescribed constant acceleration of a0 at x=0
** 
** p(x,t) = (K a0 / c^2) (ct - x)  for x < ct
**        = 0  			   for x > ct
** 
*PREPRINT,ECHO=NO,HISTORY=YES,MODEL=YES
**
*part,name=old
*NODE, Nset=ODB_NSET
    1, 0,
  101, 1,
  501, 0,.5e-2
  601, 1,.5e-2
 1001, 0, 1.e-2
 1101, 1, 1.e-2
*NGEN,NSET=CHANNEL
    1,101
 1001,1101
*NSET,NSET=SAMPLE,GENERATE
 1,101
*NSET,NSET=LOAD
 1,1001
*ELEMENT,TYPE=AC2D4
 1,1,2,1002,1001
*ELGEN,ELSET=CHANNEL
 1,100
*SOLID SECTION,MATERIAL=AIR,ELSET=CHANNEL
 1.e-2, 
** Cr-sec is 1e-4 
** ASI element at x=0, so that acceleration may be prescribed
** directly:
*ELEMENT,TYPE=ASI2,ELSET=LOAD
 1200,1001,1
*INTERFACE,ELSET=LOAD
 1.e-2,
*endpart
*part,name=new
*NODE, Nset=ODB_NSET
    1, 0,
  101, 1,
  501, 0,.5e-2
  601, 1,.5e-2
 1001, 0, 1.e-2
 1101, 1, 1.e-2
*NGEN,NSET=CHANNEL
    1,101
 1001,1101
*NSET,NSET=SAMPLE,GENERATE
 1,101
*NSET,NSET=LOAD
 1,1001
*ELEMENT,TYPE=AC2D4
 1,1,2,1002,1001
*ELGEN,ELSET=CHANNEL
 1,100
*SOLID SECTION,MATERIAL=AIR,ELSET=CHANNEL
 1.e-2, 
** Cr-sec is 1e-4 
** ASI element at x=0, so that acceleration may be prescribed
** directly:
*ELEMENT,TYPE=ASI2D2,ELSET=LOAD
 1200,1001,1
*INTERFACE,ELSET=LOAD
 1.e-2,
*endpart
**
*assembly,name=both
*instance,name=old,part=old
*endinstance
*instance,name=new,part=new
0,0.05,0
*endinstance
*nset,nset=sample
old.sample,new.sample
*nset,nset=load
old.load,new.load
*surface,NAME=NRS
 old.100,S2
 new.100,S2
*endassembly
**************************************
*MATERIAL,NAME=AIR
*DENSITY
 1.21,
*ACOUSTIC MEDIUM,BULK MODULUS
 0.1424E6,
**
**
*RESTART,WRITE
**
*STEP,INC=1000
*DYNAMIC
.0001,.0036
** Define nonreflective boundary at x=1
*IMPEDANCE
 old.100,I2,
 new.100,I2,
**
** Prescribe volume acceleration inwards
**   of  a0=1.
** Acceleration of interface element specified.
*BOUNDARY,TYPE=ACCELERATION
 LOAD,1,1,1.
*EL PRINT,FREQ=0
*NODE PRINT,NSET=SAMPLE,FREQ=6
 POR,
*NODE FILE,NSET=SAMPLE,FREQ=6
 POR,
*OUTPUT,FIELD, OP=NEW,Frequency=6
*NODE OUTPUT
 POR, 
*OUTPUT,HISTORY,OP=ADD,Frequency=6
*NODE OUTPUT,NSET=SAMPLE
 POR, 
*ENDSTEP
***********************
*STEP,INC=1000
*DYNAMIC
.0001,.0008
*IMPEDANCE,OP=NEW
*SIMPEDANCE
 NRS,
*BOUNDARY,TYPE=ACCELERATION
 LOAD,1,1,1.
*EL PRINT,FREQ=0
*NODE PRINT,NSET=SAMPLE,FREQ=6
 POR,
*NODE FILE,NSET=SAMPLE,FREQ=6
 POR,
*OUTPUT,FIELD, OP=NEW,Frequency=6
*NODE OUTPUT
 POR, 
*OUTPUT,HISTORY,OP=ADD,Frequency=6
*NODE OUTPUT,NSET=SAMPLE
 POR, 
*ENDSTEP