# Undular bores for the Green-Naghdi equations

This test case was proposed by Le Métayer et al, 2010 (section 6.2). This is a dam break problem described by the (dispersive) Green-Naghdi equations (rather than the non-dispersive Saint-Venant equations).

#include "grid/bitree.h"
#include "green-naghdi.h"

The domain is 600 metres long, centered on the origin. The acceleration of gravity is set to 10 m/s2. The problem is solved in one dimension with 2048 grid points.

int main()
{
X0 = -300.;
L0 = 600.;
G = 10.;
N = 2048;
run();
}

The initial conditions are zero velocity and a jump in fluid depth at the origin (i.e. dam break conditions).

event init (i = 0)
{
foreach() {
h[] = x < 0. ? 1.8 : 1.;
u.x[] = 0.;
}
}

event output (t = 48) {
foreach()
fprintf (stdout, "%g %g %g\n", x, h[], u.x[]);
fprintf (stdout, "\n");
}

At t = 48 seconds, the depth and velocity profiles are given below. They are compared with the numerical solution of the same problem obtained with the Saint-Venant solver (bore1.c).

The solution consists of localized undular bores superposed onto the Saint-Venant solution. This demonstrates the robustness of the numerical scheme.

set xlabel 'x'
set ylabel 'z'
set key top left
plot '../bore1/out' w l t 'Saint-Venant', 'out' w l t 'Green-Naghdi' Fluid depth profile at t = 48 seconds. (script)

set xlabel 'x'
set ylabel 'u'
plot '../bore1/out' u 1:3 w l t 'Saint-Venant', 'out' u 1:3 w l t 'Green-Naghdi' Velocity profile at t = 48 seconds. (script)