src/examples/breaking.c

    3D breaking Stokes wave (multilayer solver)

    A steep, 3D, third-order Stokes wave is unstable and breaks. This is the 3D equivalent of this test case. The bathymetry is given by \displaystyle z_b(y) = - 0.5 + \sin(\pi y)/4 i.e. it is shallower toward the back of the domain which causes the wave to break earlier there.

    Animation of the free-surface. The surface is coloured according to the x-component of the surface velocity.

    The solution is obtained using the layered model and demonstrates its robustness and a degree of realism even for this complex case.

    #include "layered/hydro.h"
    #include "layered/nh.h"
    #include "layered/remap.h"
    #include "layered/perfs.h"
    #include "view.h"

    The initial conditions are given by the wave steepness ak and the Reynolds number Re=c\lambda/\nu with c the phase speed of the gravity wave and \lambda its wavelength.

    double ak = 0.33;
    double RE = 40000.;
    
    #define k_  (2.*pi)
    #define h_   0.5
    #define g_   1.
    #define T0  (k_/sqrt(g_*k_))

    The domain is periodic in x and resolved using 256^2 points and 30 layers.

    int main()
    {
      origin (-L0/2., -L0/2.);
      periodic (right);
      N = 256;
      nl = 30;
      G = g_;
      nu = 1./RE;

    Some implicit damping is necessary to damp fast modes. This may be related to the slow/fast decoupling of the \theta-scheme mentioned by Durran & Blossey, 2012.

      theta_H = 0.51;
    
      run();
    }

    The initial conditions for the free-surface and velocity are given by the third-order Stokes solution.

    #include "../test/stokes.h"
    
    event init (i = 0)
    {

    We can use a larger CFL, in particular because we are not dealing with shallow-water/wetting/drying.

      CFL = 0.8;

    The layer thicknesses follow a geometric progression, starting from a top layer with a thickness of 1/3 that of the regular distribution.

      geometric_beta (1./3., true);
      
      foreach() {
        zb[] = - 0.5 + sin(pi*y)/4.;
        double H = wave(x, 0) - zb[];
        double z = zb[];
        foreach_layer() {
          h[] = H*beta[point.l];
          z += h[]/2.;
          u.x[] = u_x(x, z);
          w[] = u_y(x, z);
          z += h[]/2.;
        }
      }
    }

    We add (an approximation of) horizontal viscosity.

    event viscous_term (i++)
      horizontal_diffusion ((scalar *){u}, nu, dt);

    We log the evolution of the kinetic and potential energies.

    set xlabel 't/T0'
    plot [0:6]'log' u 1:2 w l t 'kinetic', '' u 1:3 w l t 'potential', \
         '' u 1:(($2+$3)/2.) w l t 'total/2'
    Evolution of the kinetic, potential and total energy (script)

    Evolution of the kinetic, potential and total energy (script)

    event logfile (i++; t <= 8.*T0)
    {
      double ke = 0., gpe = 0.;
      foreach (reduction(+:ke) reduction(+:gpe)) {
        foreach_layer() {
          double norm2 = sq(w[]);
          foreach_dimension()
    	norm2 += sq(u.x[]);
          ke += norm2*h[]*dv();
        }
        gpe += sq(eta[])*dv();
      }
      fprintf (stderr, "%g %g %g\n", t/T0, ke/2., g_*gpe/2.);
    }

    And generate the movie of the free surface (this is quite expensive). The movie is 45 seconds at 25 frames/second.

    event movie (t += 8.*T0/(45*25))
    {
      view (fov = 17.3106, quat = {0.475152,0.161235,0.235565,0.832313},
    	tx = -0.0221727, ty = -0.0140227, width = 1200, height = 768);
      char s[80];
      sprintf (s, "t = %.2f T0", t/T0);
      draw_string (s, size = 80);
      for (double x = -1; x <= 1; x++)
        translate (x) {
          squares ("u29.x", linear = true, z = "eta", min = -0.15, max = 0.6);
        }
      save ("movie.mp4");
    }

    Parallel run

    The simulation was run in parallel on the Occigen machine on 64 cores, using this script

    local% qcc -source -D_MPI=1 breaking.c
    local% scp _breaking.c user@occigen.cines.fr:
    #!/bin/bash
    #SBATCH -J breaking
    #SBATCH --constraint=HSW24
    #SBATCH --ntasks=64
    #SBATCH --threads-per-core=1
    #SBATCH --time=1:00:00
    #SBATCH --exclusive
    #SBATCH --mail-type=BEGIN,END,FAIL
    #SBATCH --mail-user=popinet@basilisk.fr
    
    module purge
    module load openmpi
    module load intel gcc
    
    NAME=breaking
    mpicc -Wall -std=c99 -O2 _$NAME.c -o $NAME \
        -I/home/popinet/local -L/home/popinet/local/gl -L/home/popinet/local/lib \
        -lglutils -lfb_osmesa -lOSMesa -lGLU -lppr -lgfortran -lm
    
    export LD_LIBRARY_PATH=/home/popinet/local/lib:$LD_LIBRARY_PATH
    export PATH=$PATH:/home/popinet/local/bin
    rm -f *.ppm
    srun --mpi=pmi2 -K1 --resv-ports -n $SLURM_NTASKS $NAME 2> log > out

    The number of timesteps was 4159 and the runtime was 44 minutes with movie generation.

    References

    [durran2012]

    Dale R Durran and Peter N Blossey. Implicit–explicit multistep methods for fast-wave–slow-wave problems. Monthly Weather Review, 140(4):1307–1325, 2012. [ DOI ]