*HEADING
1D TRANSIENT WAVE PROPAGATION IN AN ACOUSTIC MEDIUM WITH PRESCRIBED ACCEL
IN ABAQUS/EXPLICIT [AC2D3];
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=NO,MODEL=NO
*NODE, Nset=NALL
    1, 0,
  101, 1,
 1001, 0, 1.e-2
 1101, 1, 1.e-2
*NGEN,NSET=NALL
    1,101
 1001,1101
*NODE,NSET=LOAD
10001,0.0,
20001,0,1.e-2
*NSET,NSET=QA_TEST
1,101,1001,1101
*ELEMENT,TYPE=AC2D3
 1,1,2,1002
 2,1002,1001,1
*ELGEN,ELSET=CHANNEL
 1,100,1,2
 2,100,1,2
*SOLID SECTION,MATERIAL=AIR,ELSET=CHANNEL
 1.e-2, 
*surface,NAME=NRS
 199,S2
** Cr-sec is 1e-4 
*ELEMENT,TYPE=B21,ELSET=LOAD
2000,20001,10001
*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
2,S2
*SURFACE,TYPE=ELEMENT,NAME=MAIN
2000,SPOS
*TIE,NAME=COUPLING
SECONDARY,MAIN
**
*******************
*STEP
*DYNAMIC,EXPLICIT
,.0036
** Define nonreflective boundary at x=1
*IMPEDANCE
199,I2
**
*BOUNDARY,TYPE=ACCELERATION
LOAD,1,1,1.0
**
*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,1,1,1.0
**
*ENDSTEP