org-roam/20230607235645-gmsh.org

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:ID:       f2d9ff98-f926-442e-ae9b-fc1023e15b07
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#+title:  GMSH

Gmsh is a software for grid generation or meshing for the finite element method. The free software was programmed by Christophe Geuzaine and Jean-François Remacle under the GNU General Public License (GPL) and contains 4 modules:

- a graphics module to create 3-dimensional shapes
- a meshing module
- an equation solver module
- a postprocessor module
  
Gmsh is considered one of the best 3D file viewers and is used and described scientifically.  Gmsh is used after [[id:a4953b2b-81de-4c15-91e7-10d0cb5f22dd][freeCAD]] & [[id:6acf9122-b289-44e4-87e1-c3dfb5c7aeb2][salome]] to mesh the brep file after export in salome.  For better performance, Gmsh should be compiled with [[id:e56e90b1-ae5b-4344-97eb-993e5a81263e][openmpi]] in [[id:408e8348-778a-4fbd-a14d-9f3d9c595b4a][cluster]]. After meshing the Mesh is imported to [[id:2d45175d-7fcc-4a55-b81c-14da72247eef][FEA-Tool]] (as standalone-app or in [[id:e336814a-3a58-4b25-8d02-0af07623ce45][matlab]]).

An [[id:5f1df0e1-384f-4685-ae1e-fec2431b04e5][emacs]]  mode for GMSH and GetDP languages to provide indentation and nice coloring.  Add the following lines your emacs configuration file (probably ~/home/<user>//.emacs.d/init.el~): (load "~/home/<user>/.emacs.d/path/to/gmsh_getdp.el~")

* GMSH command line flags
#+begin_src bash
  gmsh -<flag> <file>.geo
#+end_src

** Geometry:
~-0~
Output model, then exit

~-tol value~
Set geometrical tolerance (Geometry.Tolerance)

~-match~
Match geometries and meshes

** Mesh:

~-1, -2, -3~
Perform 1D, 2D or 3D mesh generation, then exit

~-format string~
Select output mesh format: auto, msh1, msh2, msh22, msh3, msh4, msh40, msh41, msh, unv, vtk, wrl, mail, stl, p3d, mesh, bdf, cgns, med, diff, ir3, inp, ply2, celum, su2, x3d, dat, neu, m, key, off, rad (Mesh.Format)

~-bin~
Create binary files when possible (Mesh.Binary)

~-refine~
Perform uniform mesh refinement, then exit

~-barycentric_refine~
Perform barycentric mesh refinement, then exit

~-reclassify angle~
Reclassify surface mesh, then exit

~-reparam angle~
Reparametrize surface mesh, then exit

~-part int~
Partition after batch mesh generation (Mesh.NbPartitions)

~-part_weight [tri,quad,tet,hex,pri,pyr,trih] int~
Weight of a triangle/quad/etc. during partitioning (Mesh.Partition[Tri,Quad,...]Weight)

~-part_split~
Save mesh partitions in separate files (Mesh.PartitionSplitMeshFiles)

~-part_[no_]topo~
Create the partition topology (Mesh.PartitionCreateTopology)

~-part_[no_]ghosts~
Create ghost cells (Mesh.PartitionCreateGhostCells)

~-part_[no_]physicals~
Create physical groups for partitions (Mesh.PartitionCreatePhysicals)

~-part_topo_pro~
Save the partition topology .pro file (Mesh.PartitionTopologyFile)

~-preserve_numbering_msh2~
Preserve element numbering in MSH2 format (Mesh.PreserveNumberingMsh2)

~-save_all~
Save all elements (Mesh.SaveAll)

~-save_parametric~
Save nodes with their parametric coordinates (Mesh.SaveParametric)

~-save_topology~
Save model topology (Mesh.SaveTopology)

~-algo string~
Select mesh algorithm: auto, meshadapt, del2d, front2d, delquad, quadqs, initial2d, del3d, front3d, mmg3d, hxt, initial3d (Mesh.Algorithm and Mesh.Algorithm3D)

~-smooth int~
Set number of mesh smoothing steps (Mesh.Smoothing)

~-order int~
Set mesh order (Mesh.ElementOrder)

~-optimize[_netgen]~
Optimize quality of tetrahedral elements (Mesh.Optimize[Netgen])

~-optimize_threshold~
Optimize tetrahedral elements that have a quality less than a threshold (Mesh.OptimizeThreshold)

~-optimize_ho~
Optimize high order meshes (Mesh.HighOrderOptimize)

~-ho_[min,max,nlayers]~
High-order optimization parameters (Mesh.HighOrderThreshold[Min,Max], Mesh.HighOrderNumLayers)

~-clscale value~
Set mesh element size factor (Mesh.MeshSizeFactor)

~-clmin value~
Set minimum mesh element size (Mesh.MeshSizeMin)

~-clmax value~
Set maximum mesh element size (Mesh.MeshSizeMax)

~-clextend value~
Extend mesh element sizes from boundaries (Mesh.MeshSizeExtendFromBoundary)

~-clcurv value~
Compute mesh element size from curvature, with value the target number of elements per 2*pi radians (Mesh.MeshSizeFromCurvature)

~-aniso_max value~
Set maximum anisotropy for bamg (Mesh.AnisoMax)

~-smooth_ratio value~
Set smoothing ration between mesh sizes at nodes of a same edge for bamg (Mesh.SmoothRatio)

~-epslc1d value~
Set accuracy of evaluation of mesh size field for 1D mesh (Mesh.LcIntegrationPrecision)

~-swapangle value~
Set the threshold angle (in degrees) between two adjacent faces below which a swap is allowed (Mesh.AllowSwapAngle)

~-rand value~
Set random perturbation factor (Mesh.RandomFactor)

~-bgm file~
Load background mesh from file

~-check~
Perform various consistency checks on mesh

~-ignore_periocity~
Ignore periodic boundaries (Mesh.IgnorePeriodicity)

** Post-processing:

~-link int~
Select link mode between views (PostProcessing.Link)

~-combine~
Combine views having identical names into multi-time-step views

** Solver:

~-listen string~
Always listen to incoming connection requests (Solver.AlwaysListen) on the given socket (uses Solver.SocketName if not specified)

~-minterpreter string~
Name of Octave interpreter (Solver.OctaveInterpreter)

~-pyinterpreter string~
Name of Python interpreter (Solver.OctaveInterpreter)

~-run~
Run ONELAB solver(s)

** Display:

~-n~
Hide all meshes and post-processing views on startup (View.Visible, Mesh.[Points,Lines,SurfaceEdges,...])

~-nodb~
Disable double buffering (General.DoubleBuffer)

~-numsubedges~
Set num of subdivisions for high order element display (Mesh.NumSubEdges)

~-fontsize int~
Specify the font size for the [[id:a08570b0-8fe8-45a8-8f60-e45ea6b31a34][GUI]] (General.FontSize)

~-theme string~
Specify FLTK GUI theme (General.FltkTheme)

~-display string~
Specify display (General.Display)

~-camera~
Use camera mode view (General.CameraMode)

~-stereo~
OpenGL quad-buffered stereo rendering (General.Stereo)

~-gamepad~
Use gamepad controller if available

** Other:

~-, -parse_and_exit~
Parse input files, then exit

~-save~
Save output file, then exit

~-o file~
Specify output file name

~-new~
Create new model before merge next file

~-merge~
Merge next files

~-open~
Open next files

~-log filename~
Log all messages to filename

~-a, -g, -m, -s, -p~
Start in automatic, geometry, mesh, solver or post-processing mode (General.InitialModule)

~-pid~
Print process id on stdout

~-watch pattern~
Pattern of files to merge as they become available (General.WatchFilePattern)

~-bg file~
Load background (image or PDF) file (General.BackgroundImageFileName)

~-v int~
Set verbosity level (General.Verbosity)

~-string "string"~
Parse command string at startup

~-setnumber name value~
Set constant, ONELAB or option number name=value

~-setstring name value~
Set constant, ONELAB or option string name=value

~-nopopup~
Don’t popup dialog windows in scripts (General.NoPopup)

~-noenv~
Don’t modify the environment at startup

~-nolocale~
Don’t modify the locale at startup

~-option file~
Parse option file at startup

~-convert files~
Convert files into latest binary formats, then exit

~-nt int~
Set number of threads (General.NumThreads)

~-cpu~
Report CPU times for all operations

~-version~
Show version number

~-info~
Show detailed version information

~-help~
Show command line usage

~-help_options~
Show all options

* Convert a gmsh mesh to openfoam
- [[id:34c4e594-2aee-42d6-803a-6f843176d3b9][openFoam]] mesh conversion/manipulation tools
** ~gmshToFoam <nameofmesh>.msh~ in OpenFOAM terminal within the case directory
** ~splitMeshRegions -cellZonesOnly -overwrite~ (this is only used if there are multiple parts (volumes) to be split up) works only in main case folder, where ~.msh~ is present