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Introduction and Files

This documentation will explain the basis behind the CFD process. Below flowchart shows the global steps necessary to make an analysis.

Model & Mesh

First step is to make a model of the part we want to simulate. Although dolfyn’s input file format is easy to understand, it is quite a hassle to make an actual model. To this end, we recommend using Gmsh.

What is Gmsh?

Gmsh is an automatic 3D finite element grid generator with a built-in CAD engine and post-processor. Its design goal is to provide a simple meshing tool for academic problems with parametric input and advanced visualization capabilities. Gmsh is developed by Christophe Geuzaine (University of Liège) and Jean-François Remacle (Catholic University of Louvain). See for all other Gmsh info: http://gmsh.info/.

What about Meshing?

This program also enables you to generate a mesh for your 3D model. Furthermore, a converter from a gmsh-mesh file to dolfyn-compatible files is included in the packaged download.

Simulating

Once the model is finished the desired simulation can be run. This will be done using the dolfyn software.

Should I have knowledge?

Yes, you should have an understanding of what CFD is, and of fluid dynamics in general. The dolfyn software uses the converted mesh and a specific input file containing all control parametersmaterial properties, and boundary conditions for the simulation. To be able to understand this file you will need to have basic understanding of the influences to the dynamic effects in fluids.

Visualising & Analysing

Last step is to evaluate and visualise what has been run. This step can be done using multiple different software packages, among which also Gmsh. For this reason, the first couple of tutorials will use it as to not add more complexity than necessary.

Later tutorials will use VisIt, because of its more powerful nature, and the possibility to script its use. You should, however, still be able to use the knowledge of the first tutorials to finish this walk-through using only Gmsh.

Files used

Contents of the tutorials (showing some of Gmsh’s features):

  • First simple tet model with in- and outlet.
  • Same geometry, with tetrahedrals only (t3a) or using wedges (t3b).
  • The fourth model shows a nice mix of hexahedral and triangluar cells.
  • A very complicated fifth model (tet only).
  • The sixth model is a hexahedral model.
  • The seventh model shows how to deal with STL data.

Final Note

This tutorial is written for both Linux and Windows users, and has been reviewed using both. Nevertheless, understanding what you are doing is important, so please read carefully before contacting us. Do not hesitate, however, to do so in case you find something wrong or unclear.

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