[Gmsh] Using Gmsh as a post-processor

Rami Ben-Zvi rami.ben-zvi at weizmann.ac.il
Tue Oct 19 12:05:22 CEST 2010


I am new to Gmsh (running gmsh-2.4.2-Windows on a Windows XP system). I 
use it as a post-processor to my own heat transfer code (simulation of a 
novel solar steam generator), having also a dedicated home-made mesh 
generator. In order to view the results with Gmsh, my heat transfer code 
writes two ASCII files in Gmsh format at the end of the run. The first 
contains the mesh (nodes and both 1D and 2D elements in 3D space), and 
the second (merged file) - the nodal and element results. The results 
comprise of various quantities:

    * For the 1D fluid elements, the nodal values of fluid temperature,
      pressure, steam quality and other fields.
    * For part of the 2D solid elements, nodal values are the solid
      temperature, and element values of conductive fluxes, heat
      transfer coefficients and other fields.
    * For another part of the 2D solid elements, element values are the
      incident and net radiative fluxes, average temperature and other

The above is mainly intended as a background to the following questions:

    * Is it possible in Gmsh to display results along line of nodes and
      elements as x-y graphs (e.g., the solid and fluid nodes and
      elements temperature fields along an axial line)? At present I do
      it manually, by importing parts of the output into Excel, which is
      rather cumbersome. _/The answer to this question is therefore the
      most urgent./_
    * The geometry of the steam generator we develop is rather
      inconvenient to display, since it comprises of several concentric
      cylinders having narrow gaps between each other, and also having
      bases. In order to display the results, it would be convenient if
      parts of the model can be unselected, so that only desirable parts
      temperatures contours, say, are displayed. The way I do it now is
      by defining many views (around 100), each devoted to a certain
      group of the nodes or element and a certain field values. Is there
      a more elegant and simpler way to do it? Are the "Physical Names"
      properties useful for this? There is very limited documentation of
      their use in the post-processing part of Gmsh (provided I do
      /*not*/ use Gmsh geometry and mesh processors).
    * For the former issue, it would be beneficial for my geometry if
      results could be displayed in a cylindrical coordinate system. Is
      it possible? At present I generate an alternative nodes and
      element file, where the nodal coordinates are in r-q-z rather than
      x-y-z (BTW, I have noticed that the elements cannot be input on a
      separate file. Why?), but find it quite inconvenient and wasteful.
    * Is there a way to scale differently the various coordinates? It
      would be convenient for slender geometries in general, e.g, a high
      length-to-diameter-ratio cylinder.
    * A tiny-but-irritating problem - whenever I start Gmsh GUI and wish
      to open or merge files, it starts at a certain folder where Gmsh
      executable resides, rather that the folder I start from (where the
      post- files and a link to the Gmsh executable reside). How do I
      customize it to start browsing for these files from the current
      (or other) folder?

Thank you, and chapeaux for the good work you are doing,
Rami Ben-Zvi
Solar Research Facilities Unit           Tel.   +972-8-9343397
Weizmann Institute of Science            Fax    +972-8-9344117
Rehovot  76100,  ISRAEL                  Mobile +972-54-6279767
e-mail: rami.ben-zvi at weizmann.ac.il      Home   +972-8-9349223

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