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docs:utils:field2ascii

field2ascii

convert a binary flowfield file (.ff) to an ascii data file (.asc)

options

  -p        --padding                  save full Nx x Ny x Nz grid rather eliminating padded modes
  -g        --gridpoints               write x.asc, y.asc, z.asc gridpoint files
  <fieldname>      (trailing arg 2)    flowfield input file
  <asciifile>      (trailing arg 1)    ascii output file

usage

  field2ascii u.ff u.asc  

ASCII files are stored as physical values of components of the field at the gridpoints (i.e. not spectral coefficients). Fields with 2/3-style padding for dealiasing are saved on reduced grids (Nx,Nz → 2Nx/3, 2Nz/3), unless the -p option is used.

ASCII velocity fields

The gzipped ASCII velocity files store gridpoint values of the field in x,y,z,i order using the following C++ code

os << setprecision(16);
for (int nx=0; nx<Nx ++nx)
  for (int ny=0; ny<Ny ++ny)
    for (int nz=0; nz<Nz ++nz)
      for (int i=0; i<Nd ++i)
        os << u(nx,ny,nz,i) << '\n';

The value u(nx,ny,nz,i) is the ith component of the Nd-dimensional field at the gridpoint (nx,ny,nz). The (nx,ny,nz)th gridpoint has spatial coordinates (nx Lx/Nx, cos(ny pi/(Ny-1)), nz Lz/Nz). For 3D velocity fields, the (u,v,w) components are i=0,1,2.

ASCII geometry and discretization

Geometrical and discretization parameters are stored as ASCII in *.geom files as follows

  32                      %Nx
  35                      %Ny
  32                      %Nz
  3                       %Nd
  5.511566058929462       %Lx
  2.513274122871834       %Lz
  0.8771929824561405      %lx=Lx/(2pi)
  0.4                     %lz=Lz/(2pi)
  1.14                    %alpha=2pi/Lx
  2.5                     %gamma=2pi/Lz

In channelflow, Lx and Lz are the canonical geometry specifications. The .geom files provide lx,lz and alpha,gamma for human convenience.

docs/utils/field2ascii.txt · Last modified: 2010/02/02 07:55 (external edit)