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  4. Meshing and Simulating

Meshing and Simulating

Meshing

Start Gmsh and create the mesh with:

gmsh -3 t6.geo

Possible output

Start Gmsh and create the mesh with:

gmsh -3 t6.geo

Info    : Running 'gmsh -3 t6.geo' [Gmsh 4.0.4, 1 node, max. 1 thread]
Info    : Started on Tue Nov 13 15:36:08 2018
Info    : Reading 't6.geo'...
Info    : Reading 't1.geo'...
Info    : Done reading 't1.geo'
Info    : Done reading 't6.geo'
Info    : Meshing 1D...
Info    : Meshing curve 1 (Line)
. . .
Info    : Meshing curve 32 (extruded)
Info    : Done meshing 1D (0 s)
Info    : Meshing 2D...
Info    : Meshing surface 1 (transfinite)
. . .
Info    : Meshing surface 38 (extruded)
Info    : Done meshing 2D (0 s)
Info    : Meshing 3D...
Info    : Meshing volume 1 (extruded)
Info    : Done meshing 3D (0 s)
Info    : Optimizing 3D mesh...
Info    : Done optimizing 3D mesh (0 s)
Info    : 1200 vertices 1959 elements
Info    : Writing 't6.msh'...
Info    : Done writing 't6.msh'
Info    : Stopped on Tue Nov 13 15:36:09 2018

Opening t6.msh will show something similar to:

As can be seen, the mesh consists of quadrangles, and is finer near the extremities of line 2 (top one in this view).

Copying mesh

Again, to make sure the mesh file will not be overwritten by the results, we copy and rename the files:

cp t6.msh t6d.msh

Converting to dolfyn input

We now convert the mesh into *.cel, a  *.vrt, a  *.bnd, and optionally an  *.inp file using gmsh2dolfyn, and selecting the correct file to convert, in our case: t6d.

gmsh2dolfyn t6d

Possible output

Start gmsh2dolfyn converter with:

gmsh2dolfyn t6d
 Gmsh2Dolfyn: Converts a Gmsh mesh file to Dolfyn format.
 Input must be in Gmsh version 2.0, 2.1, 2.2 or 4 ascii format.
 Opening the Gmsh file
 File t6d.msh opened
 Reading MeshFormat
 MeshFormat: 4 0 8
 Reading PhysicalNames
 Name            2 -> Top
 Name            3 -> Left
 Name            4 -> Right
 Name            5 -> Bottom
 Name            6 -> Front
 Name            7 -> Back
 Name            1 -> Fluid
 Entities
 Entity            1  surface            7 Back                                  
  . . .
 Entity            1  volume             1 Fluid
 Physical entities found            9
 Reading Nodes
 Number of entity blocks:          33  Nodes:        1200
 Creating the dolfyn .vrt file
 File t6d.vrt opened
 Point              1  Node            1
  . . .
 Surface           38  Nodes         504
 Nodes written         1200
 Gmsh 4: Total Gmsh Entity Blocks to be read in:           9
 Gmsh 4: Total Gmsh elements to be read in:        1749
 Creating the dolfyn .cel and .bnd files          14          23
 File t6d.cel opened
 File t6d.bnd opened
 Element            1 Back     Type            3         551
  . . .
 Element            1 Fluid    Type            5         551
 Quad boundaries:             1198
 Hexahedral cells:             551
 Writing the .inp file
 File t6d.inp opened
 inp:           2 Top          T
 inp:           3 Left         T
 inp:           4 Right        T
 inp:           5 Bottom       T
 inp:           6 Front        T
 inp:           7 Back         T
 Done gmsh2dolfyn 2018

Running Pre-Processor

Now we will run the pre-processor.

dolgeo -s 1.0 -b t6d

If no options are given with the dolgeo command, you will be prompted for them. Fill in case name t6d, scaling factor of 1.0 (default) and bin as format of geometry file.

Possible output

The pre-processor is run with:

dolgeo -s 1.0 -b t6d
 Dolfyn PreProcessor
 t6d                              T T T F
 Using command line arguments
 Using t6d as input
 Opening vertex file
 Initialise vertex list
 . . .
 Region ID:            2  => Top
 Region ID:            3  => Left
 Region ID:            4  => Right
 Region ID:            5  => Bottom
 Region ID:            6  => Front
 Region ID:            7  => Back
 Type 1 regions found:           6           7
 WARNING: check inp-file
 Using:    1.00000000      binary
 Dump binary geometry file
 Done

Running Simulation

Finaly we will run the dolfyn simulations.

dolfyn t6d

If no case name is inputted directly, you will be prompted. If so, enter case name t6d.

Possible output

The pre-processor is run with:

dolfyn t6d
 This is dolfyn version 0.607
 Copyright(C) 2002-2016 Cyclone Fluid Dynamics BV
 NL-5583 XM, Waalre, The Netherlands
 see http://www.cyclone.nl and https://www.dolfyn.net

 Using Sparsekit2 by Yousef Saad
 (C) 2005, the Regents of the University of Minnesota
 Modules with patches (C) 2004-2010 by B. Tuinstra
 see http://www.home.zonnet.nl/bouke_1/dolfyn
 Tecplot interface (tecplt.f90) (C) 2006-2012 by
 S.B. Kuang, UNSW, Sydney, Australia
 VTK interface updated (C) 2007 by J. Jacobs
 Static boundary conditions (C) 2011 by J. JoJo
 MKL contributions and suggestions by Runar


 Using case: t6d
 Calling dolfyn t6d .dge
 t6d.dge binary
. . .

 *** CONVERGENCE ***   8.98416969E-04
 Opening restart file
 File t6d.rst
 Restartfile 400 written

 Writing Full Gmsh file...
 Done
 Maximum change in PP:   2.36398118E-04   8.98416969E-04   1.00000005E-03
 Arrays cleaned up
 Done t6d
 Bye!

That’s it! Now all the calculations have been carried out, we can start to analyze the output.

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