discharge_bug.c

Bug with imposed inflow

Bug with imposed inflow

The case studied here is a topography descending towards the y decreasing with a parabolic bed of which one digs a little more the center. We use the function eta_b to impose a flow on the top edge. We study the water elevation to see if it is regular. We check that the imposed inflow is equal to the one entering the domain.

#include "layered/hydro.h"
#include "riemann.h"
//#include "saint-venant.h"
#include "discharge.h"

#define LEVEL 8

int main()
{
  size (10.);
  origin (- L0/2., - L0/2.);
  G = 9.81;
  N = 1 << LEVEL;
  run();
}

u.n[top] = neumann(0);

The flow rate varies in time and is set by computing the the elevation \eta_s of the water surface necessary to match this flow rate.

double etas;
double inflow_imp;

event inflow (i++) { 
  if (t < 1)
    inflow_imp = 0.5*t;
  else
    inflow_imp = 0.5;
  etas = eta_b (inflow_imp, top);
  h[top] = max (etas - zb[], 0.);
  eta[top] = max (etas - zb[], 0.) + zb[];
}

Initial conditions

event init (i = 0)
{  

  DT = 1e-2;

  foreach(){
    if (x*x < 1)
      zb[] = 5*(x+1)*(x-1)+(x*x*0.01 + y)/2.;

    else
      zb[] = (x*x*0.01 + y)/2.;
  }
  boundary ({zb});
}

Outputs

We compute the time-derivative of the total water volume (i.e. the net flow rate), and make a GIF movie.

event logfile (i++; t <= 2.) {
  static double volo = 0., to = 0.;
  double vol = statsf(h).sum;
  if (i > 0)
    fprintf (ferr, "%g %.6f %.6f %g %g\n", t, (vol - volo)/(t - to), inflow_imp,vol, etas);
  volo = vol, to = t;
}

event output (i += 5) {
  output_ppm (h, min = 0, max = 0.1, file = "riverbug.gif");
}

Results

Le débit est différent de celui imposé.

set key top left
set xlabel 'Time'
set ylabel 'Flow rate'
plot './log' u 1:2 w l t 'obtained', \
         './log' u 1:3 w l t 'imposed'

Evolution of the flow rate (script)

Le débit est irrégulier

Evolution of the water level