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General information on Gmsh and dolfyn

Gmsh is geared towards numerical strength analysis based on the Finite Element Method. This means that “points” and “bars” (1D and 2D elements) are important. Dolfyn however only works with 3D (fluid) cells and uses a separate boundary file (*.bnd). Note that dolfyn cannot use the concept of 2D “shell models”. Gmsh’ Physical Surfaces are used as dolfyn boundaries.

When the mesh is written by gmsh only “physical entities” are written out the the *.msh file. “Physical Points” and “Physical Lines” are useless to dolfyn and will interfere with the communication from Gmsh to and from dolfyn.

Another issue is that both Gmsh and dolfyn use a *.geo file. The *.geo file for Gmsh contains commands to create a mesh. Dolfyn’s preprocessor creates a *.geo file form the geometrical files (*.cel, *.vrt, *.bnd and optionally *.inp). When the preprocessor overwrites the orginal Gmsh *.geo file then it’s contents will be lost. One solution is to rename the *.msh file made by Gmsh (see the following tutorials).

Also a newer version of the preprocessor is needed (newer than april 2009). Up until now the preprocessor did not use the order of the boundary definitions in the *.bnd file. The order is important to Gmsh and the interface dolfyn2gmsh.

Finally do not forget to compile gmsh2dolfyn.f90.

Using Gmsh as post-processor

Of course one can use any output and postprocessor. However, if you want to use Gmsh, insert one of the following to the *.din file, such that a *.msh file will be written:

  • use gmsh  – a file with results only.
  • use gmsh fluid – a full file, but the results on the boudaries will be ommitted.
  • use gmsh full – a full file containing the mesh, boudaries (including the default boundaries, region 0) will be written.

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