Mesh generator interfaces

The mesh generator interface provides the link to a specific mesh generator. It is selected by the meshpackage parameter of an adaptive analysis; see Adaptive linear static and Adaptive nonlinear static. The parameters of the interface (including remeshcmd and the Gmsh parameters below) are given in the analysis record; they are supported by both adaptive analyses.

All mesher-specific details are hidden behind the interface. When asked for a new mesh, the interface either returns the new mesh directly (built-in subdivision, or an external mesh generator run by the interface), or writes the required mesh density into a mesher-specific file only, leaving the remeshing to the user.

MPT_T3D — meshpackage = 0

T3d mesh interface. The default. Supports 1D, 2D (triangular) and 3D (tetrahedral) meshes. Writes the background mesh file t3d.bmf.

MPT_TARGE2 — meshpackage = 1

Interface to the Targe2 2D mesh generator. Writes targe2.bmf.

MPT_FREEM — meshpackage = 2

Interface to the Freem 2D mesh generator. Writes freem.bmf.

MPT_SUBDIVISION — meshpackage = 3

Built-in subdivision algorithm. Supports triangular 2D and tetrahedral 3D meshes, and can operate in parallel mode. Creates the new mesh directly.

MPT_GMSH — meshpackage = 4

Interface to the Gmsh mesh generator. The required element size is written as a Gmsh background mesh (post-processing view, file <output>.bgm.<n>.pos), built from the current mesh (triangles, quads, tetrahedra, hexahedra and wedges are supported), so the current mesh can come from any source. When the geometry and control files are given, the interface runs Gmsh and converts the mesh to the new oofem domain using tools/unv2oofem/gmsh2oofem.py; the properties (cross sections, materials, boundary conditions, loads and sets) are assigned to the mesh based on Gmsh physical groups, as described in the unv2oofem control file. The same script generates the initial mesh:

gmsh2oofem.py [--dim 3] [--elemtype simplex|quad|hex] [--setnumber lc 0.1] model.geo model.ctrl model.in

(--setnumber sets a geometry parameter declared by DefineConstant in the geometry file, e.g. the initial mesh size.)

Parameters:

[gmshgeo (s)]

Gmsh geometry file (.geo).

[gmshctrl (s)]

unv2oofem control file.

[gmshopts (s)]

Additional options of gmsh2oofem.py, for example "--elemtype hex" (hexahedral mesh obtained by subdivision of tetrahedra) or "--option Mesh.Algorithm=6".

[gmshgrading (rn)]

Limits the gradation of the required element size field written to the background mesh: the size at any node is reduced to at most \(h_j + g\,|x_i - x_j|\) for every node \(j\) of the current mesh, so that the transition from fine to coarse mesh is gradual. Gmsh itself provides no such control for background meshes. Default 0 (not limited); values of 0.1–0.25 are typical.

[gmshcmd (s)]

Gmsh executable, default gmsh.

[pythoncmd (s)]

Python interpreter, default python3.

[gmsh2oofem (s)]

Path to the conversion script, by default the script in the oofem source tree.

External remeshing

The interfaces writing a mesh density file (T3d, Targe2, Freem, Gmsh) can run an external mesh generator and converter themselves, when the command is given by the remeshcmd parameter. The command has to create the new oofem domain file (the oofem input file starting with the domain record). The following placeholders are substituted before the command is executed:

%d

the mesh density file written by the interface,

%o

the domain file to be created (<output>.domain.1.<n>.din),

%s

the serial number of the new domain,

%n

the solution step number,

%%

the percent character.

For example, with T3d:

remeshcmd "t3d -i job.t3d -m %d -o job.t3d.out && t3d2oofem job.ctrl job.t3d.out job.in && tail -n +4 job.in > %o"