*HEADING
1D TRANSIENT WAVE PROPAGATION IN AN ACOUSTIC MEDIUM WITH PRESCRIBED ACCEL 
IN ABAQUS/EXPLICIT [AC3D8R]; 
VERIFICATION PROBLEM: TRANSIENT DYNAMICS TESTS
**
** C=SQRT(K/RHO)= 343.05 M/S   K=BULK MODULUS, 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
** THE ACCELERATION IS SPECIFIED USING *BOUNDARY, TYPE=ACCELERATION
**
*PREPRINT,ECHO=NO,HISTORY=NO,MODEL=NO
*NODE, Nset=QA_TEST
    1, 0,
  101, 1,
 1001, 0, 1e-2
 1101, 1, 1e-2
 1501, 0, 1e-2, -1e-2
 1601, 1, 1e-2, -1e-2
 2501, 0, 0, -1e-2
 2601, 1, 0, -1e-2
*NGEN,NSET=NALL
    1,101
 1001,1101
 1501,1601
 2501,2601
*NSET,NSET=NALL
NALL, QA_TEST
*NODE,NSET=LOAD
10001, 0,
10002, 0, 1e-2
10003, 0, 1e-2, -1e-2
10004, 0, 0, -1e-2
10005, -0.1e-2,
10006, -0.1e-2, 1e-2
10007, -0.1e-2, 1e-2, -1e-2
10008, -0.1e-2, 0, -1e-2
*ELEMENT,TYPE=AC3D8R
 1,1,2,2502,2501,1001,1002,1502,1501
*ELGEN,ELSET=CHANNEL
 1,100
*SOLID SECTION,MATERIAL=AIR,ELSET=CHANNEL
*surface, NAME=NRS
 100,S4
*ELEMENT,TYPE=C3D8R,ELSET=LOAD
200,10001,10004,10008,10005,10002,10003,10007,10006
*SOLID SECTION,MATERIAL=MAT1,ELSET=LOAD
*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,S6
*SURFACE,TYPE=ELEMENT,NAME=MAIN
200,S3
*TIE,NAME=COUPLING
SECONDARY,MAIN
*******************
*STEP
*DYNAMIC,EXPLICIT,ELEMENT BY ELEMENT
,.0036
** Define nonreflective boundary at x=1
*IMPEDANCE
 100,I4
**
** Prescribe volume acceleration a0=1.
** Acceleration of interface element specified.
** In order to run single precision, the reference
** magnitude is increased to 1000.
**
*BOUNDARY,TYPE=ACCELERATION
LOAD,1,1,1.E3
****
***************************
*OUTPUT,FIELD,NUMBER INTERVAL=1
*NODE OUTPUT
POR
*NODE OUTPUT,NSET=QA_TEST
POR,
***************************
***OUTPUT,HISTORY, FREQ=10
***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.E3
*ENDSTEP