PHOTON USE
  p; parphi;  1 1 500
 
  gr ou y 1
  msg pressure; distance is vertical, time horizontal
  con p1 y 1 fi;1
  msg Press  to continue
  pause;con off;red
  msg velocity; distance is vertical, time horizontal
  con u1 y 1 fi;1
  enduse
 
    GROUP 1. Run title and other preliminaries
TEXT(Pressure Waves From Valve Closure
TITLE
  DISPLAY
  Air is moving steadily along a pipe. Valves are suddenly closed
  at each end, bringing the air to rest there. The subsequent
  distributions of velocity and pressure in the pipe are to be
  predicted.
 
  The analysis is one-dimensional, and the process is supposd to
  be isentropic, ie without either friction or heat transfer.
 
  ENDDIS
    GROUP 2 and 3
STEADY=F; tlast=0.01; lstep=100; xulast=2.0; nx=100
l(unigrid
 
    GROUP 7. Variables stored, solved & named
SOLVE(P1,U1); STORE(RHO1)
 
    GROUP 8. Terms (in differential equations) & devices
  ** De-activate the diffusion term in the U1 equation
TERMS(U1,Y,Y,N,Y,Y,Y)
 
    GROUP 9. Properties of the medium (or media)
#FLUIDMAT
SETPRPS(1,AIRISENT)
REAL(REFPRE,REFRHO);REFPRE=1.E5;REFRHO=1.0
MESG(Isentropic Air, Refrho=:REFRHO:, Refpre=:REFPRE:
RHO1A=REFRHO*(1.0/REFPRE)**RHO1B
 
    GROUP 11. Initialization of variable or porosity fields
FIINIT(P1)=REFPRE; FIINIT(U1)=1.0; FIINIT(RHO1)=REFRHO
 
    GROUP 15. Termination of sweeps
LSWEEP=10
 
    GROUP 22. Spot-value print-out
IXMON=NX/2; TSTSWP=-1
SPEDAT(SET,GXMONI,TRANSIENT,L,F)  
    GROUP 23. Field print-out and plot control
NTPRIN=LSTEP/5;NXPRIN=NX/5
 
PATCH(ALLX,PROFIL,1,NX,1,1,1,1,1,LSTEP)
PLOT(ALLX,P1,0.0,0.0); PLOT(ALLX,U1,0.0,0.0)
 
PATCH(TIMEPLOT,PROFIL,NX/2,NX/2,1,1,1,1,1,LSTEP)
PLOT(TIMEPLOT,P1,0.0,0.0); PLOT(TIMEPLOT,U1,0.0,0.0)
 
  create parphi file for display via PHOTON
IDISPA=1;IDISPB=1;IDISPC=LSTEP