*HEADING
1D TRANSIENT WAVE PROPAGATION IN AN ACOUSTIC MEDIUM WITH PRESCRIBED ACCEL
IN ABAQUS/EXPLICIT [ACAX4R];
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=NALL
ODB_NSET, CHANNEL, SAMPLE
*NODE,NSET=LOAD
10001,0.0,
20001,1.e-2,0.
*ELEMENT,TYPE=ACAX4R
 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 
*ELEMENT,TYPE=B21,ELSET=LOAD
200,10001,20001
*BEAM SECTION,MATERIAL=MAT1,ELSET=LOAD,SECTION=RECT
 0.3,3
*MATERIAL,NAME=MAT1
*ELASTIC
 180E2,0.333333
*DENSITY
 76.70,
*MATERIAL,NAME=AIR
*DENSITY
 1.21,
*ACOUSTIC MEDIUM,BULK MODULUS
 0.1424E6,
*********************************
*SURFACE,TYPE=ELEMENT,NAME=SECONDARY
1,S1
*SURFACE,TYPE=ELEMENT,NAME=MAIN
200,SPOS
*TIE,NAME=COUPLING
SECONDARY,MAIN
*****************
*NSET, NSET=QA_TEST
ODB_NSET
**
**
*STEP
*DYNAMIC,EXPLICIT
,.0036
** Define nonreflective boundary at x=1
*IMPEDANCE
100,I3
**
*BOUNDARY,TYPE=ACCELERATION
LOAD,1,2,1.0
**
*OUTPUT,FIELD,NUMBER INTERVAL=1
*NODE OUTPUT
POR
*NODE OUTPUT,NSET=QA_TEST
POR,
***OUTPUT,HISTORY, FREQ=1
***NODE OUTPUT, NSET=QA_TEST
**POR
*ENDSTEP
*STEP
*DYNAMIC,EXPLICIT
,.0008
** Define nonreflective boundary at x=1
*IMPEDANCE,OP=NEW
*SIMPEDANCE
NRS
**
*BOUNDARY,TYPE=ACCELERATION
LOAD,1,2,1.0
**
*ENDSTEP