Tet2Hex for Nek5000/NekRS

This code generates the Hexahedral mesh in Nek5000/NekRS .re2 format based on tet-to-hex approach.
This is a subset of my other code, SphereMesh, for the pebble-bed mesh generation. All right reserved.

Usage 1: arbitraty 3d points

• Main driver: driver1.m

• Specify the input points into variable P (#pts,3).
  This can be arbitrary 3D points. For examples:

  • Template 1: single tet

     P=[0,0,0; 1,0,0; 0,1,0; 0,0,1];
  

  • Template 2: uniform lattice

     L = 3; W = 2; H = 1; % length, width and height of box 
   
     xx=linspace(0,L,11);
     yy=linspace(0,L,7);
     zz=linspace(0,L,3);
   
     [X,Y,Z] = meshgrid(xx,yy,zz);
     P=[X(:),Y(:),Z(:)];
  

  • Template 3: random ponts in a 3D box

     L = 3; W = 2; H = 1; % length, width and height of box
     npts = 201;  % # pts
  
     P = zeros(npts,3); rng(23); % for reproducible
     P(:,1) = L*rand(1,npts); % x-coordinate of a point
     P(:,2) = W*rand(1,npts); % y-coordinate of a point
     P(:,3) = H*rand(1,npts); % z-coordinate of a point
  

  • Template 4: uniform points in an unit sphere

     npts=1000;
     x=normrnd(0,1,npts,1);
     y=normrnd(0,1,npts,1);
     z=normrnd(0,1,npts,1);
     R=rand(npts,1).^(1/3);
     R=R./sqrt(x.^2+y.^2+z.^2);
     P = [x.*R, y.*R, z.*R];
  

  • Template 5: read points from a file
    Use save('output/input.txt','P','-ascii'); to see the example format

     P = load('data/input.txt'); P = P(:,1:3);
  

• The code will generate the following files under the output/ directory

  • mesh.re2: Nek re2
  • mesh.co2: Nek co2
  • logfile: re-direct the printed info from terminal to the logfile.
    The previous logfile will be backup to logfile.1
  • Hexes_Hini.vtk: the vtk file for the mesh (ifdump=1). This can be opened via ParaView/Visit

Usage 2: arbitrary 2d points + extrusion

• Main driver: driver2.m

  This generates the sampling points on sphere surface, tesselate the convexhull into triangles, splits each triangle into 3 quadrilaterals, then extrudes inward to get a sphere shell mesh.

Notes

• Currently, Octave is not supported.
• All boundaries are set to wall 'W ' since there is no other info.
• The function dump_nek_re2 is not the fastest version. Potential slow-down for E > 10M.
• The tet2hex is the first edition, this can be sped up further.