Hex mesh for salt work
This is a 8x80 foot tunnel with mesh out to 200 ft in xz, and 80 ft in y
Target resolution along tunnel walls near .1 then .5 at 40, ratio to big to outside.
Tunnel is empty of elements

goal is 100,000 nodes but is not possible with .1 for 8 feet resolution.
This coarse version mesh has .2 feet spacing at tunnel
then expands in size space quickly toward Y axis and in XZ

number of nodes =        360450        number of elements =       344960    
dimensions geometry =         3        element type =                hex    
dimensions topology =         3        8 nodes      6 faces     12 edges    

min aspect ratio =  0.4513E+00      max aspect ratio =  0.1000E+01                  
min volume       =   8.1000000E-03  max volume       =   1.4437500E+03                      

--------------------------------------------------------------------------

directory /vers_coarse
Coarse Hex mesh for setup 

This is a 8x80 foot tunnel with mesh out to 200 ft in xz, and 80 ft in y
Resolution along tunnel walls is .8 and increases outward.
Tunnel is empty of elements

number of nodes =         88711        number of elements =        80640
dimensions geometry =         3        element type =                hex
dimensions topology =         3        8 nodes      6 faces     12 edges

min aspect ratio =  0.8314E+00  max aspect ratio =  0.1000E+01
min volume       =   8.5000000E-02  max volume   =  6.4000000E+02



=======================================================================
Method:

Create the 2D quad surface on XZ plane
Resolution is setup with 5 rings from inner to outer
  lagrit < surf_quad.lgi

Extrude and stack into hex mesh
  write_hex_lgi.py > hex.lgi
  lagrit < hex.lgi

Check result
grep Dudd outx3dgen

remove zero volumes and write final files
  lagrit < hex_final.lgi



=======================================================================
The subdirectories have attempts starting at high resolution then
each iteration is coarser until version used in this directory (vers 3)

Try .1 spacing for inner 8 feet 
  In directory vers_space_1
  The new point count is     25277.                                            
  144* 25277 = 3639888
  100* 25277 = 2527700 

Try .2 spacing for inner 8 feet
  In directory vers_space_2
  The new point count is     9477.
  80* 9477 = 758160 

Try .2 spacing and half resolution other places
  In directory vers_space_half_all
  The new point count is     7533.
  80* 7533 = 602640
  60* 7533 = 451980

Try .2 spacing and reduce resolution throughout 
  In directory vers_3
  The new point count is      7209.
  Near same resolution as xz 70 * 7209 = 504630
  Largest possible resolution 51*7209 = 367659
  .2 until 8 feet
  .4
  .6
  1.0
  2.0
  4.0
  8.0
  -- 24
  16.
  -- 40
  20.
  20.
  -- 80