*HEADING
EC28AFAS: 1D transient wave propagation in an acoustic medium with prescribed acceleration on DOF 1. AC2D8,ASI3
 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
*NGEN,NSET=CHANNEL
*NSET,NSET=SAMPLE,GENERATE
*NSET,NSET=LOAD
*ELEMENT,TYPE=AC2D8
*ELGEN,ELSET=CHANNEL
*SOLID SECTION,MATERIAL=AIR,ELSET=CHANNEL
 1.e-2,
** Cross-section is 1e-4
** ASI element at x=0, so that acceleration may be prescribed
** directly:
*ELEMENT,TYPE=ASI3,ELSET=LOAD
*INTERFACE,ELSET=LOAD
*endpart
*part,name=new
*NODE, Nset=ODB_NSET
*NGEN,NSET=CHANNEL
*NSET,NSET=SAMPLE,GENERATE
*NSET,NSET=LOAD
*ELEMENT,TYPE=AC2D8
*ELGEN,ELSET=CHANNEL
*SOLID SECTION,MATERIAL=AIR,ELSET=CHANNEL
 1.e-2,
** Cross-section is 1e-4
** ASI element at x=0, so that acceleration may be prescribed
** directly:
*ELEMENT,TYPE=ASI2D3,ELSET=LOAD
*INTERFACE,ELSET=LOAD
*endpart
**
*assembly,name=both
*instance,name=old,part=old
*endinstance
*instance,name=new,part=new
*endinstance
*nset,nset=sample
old.sample,new.sample
*nset,nset=load
old.load,new.load
*surface,NAME=NRS
 old.50,S2
 new.50,S2
*nset,nset=channel
old.channel,new.channel
*endassembly
**************************************
*MATERIAL,NAME=AIR
*DENSITY
 1.21,
*ACOUSTIC MEDIUM,BULK MODULUS,DEP=2
*RESTART,WRITE
**
*INITIAL CONDITIONS,TYPE=FIELD,VAR=2
CHANNEL,1
**
*STEP,INC=1000
*DYNAMIC,DIRECT
.0001,.0036
** Define nonreflective boundary at x=1
*IMPEDANCE
 old.50,I2
 new.50,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,DIRECT
.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