*HEADING
EC13AFAS: 1D transient wave propagation in an acoustic medium with prescribed acceleration on DOF 1. AC1D3,ASI1
 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=YES
*NODE
    1,0,
  101,1
*NGEN
   1,101
*NSET,NSET=CHANNEL,GENERATE
 1,101
*NSET,NSET=LOAD
 1,
*ELEMENT,TYPE=AC1D3
 1,1,2,3
*ELGEN,ELSET=CHANNEL
 1,50,2
*SOLID SECTION,MATERIAL=AIR,ELSET=CHANNEL
 3., 
** Cross-section is 3.0  
*** ASI element at x=0, so that acceleration may be prescribed
** directly:
*ELEMENT,TYPE=ASI1,ELSET=LOAD
 200,1
*INTERFACE,ELSET=LOAD
 3.,1,0,0
**
*MATERIAL,NAME=AIR
*DENSITY
 1.21,
*ACOUSTIC MEDIUM,BULK MODULUS
 0.1424E6,
**
**
*RESTART,WRITE
**
*STEP,INC=1000
*DYNAMIC,DIRECT
.0001,.0044
** Define nonreflective boundary at x=1
*IMPEDANCE
 50,I2
**
** Prescribe volume acceleration inwards
**   of  a0 * cross-section= 3., therefore a0=1
** Acceleration of interface element specified.
*BOUNDARY,TYPE=ACCELERATION
 LOAD,1,1,1.
*EL PRINT,FREQ=0
*NODE PRINT,NSET=CHANNEL,FREQ=22
 POR,
*OUTPUT,VAR=PRESELECT,FIELD,FREQ=1
*OUTPUT,VAR=PRESELECT,HISTORY,FREQ=1
*ENDSTEP