[klaus]

Dear OpenFoam friends,

with the new version of cgx (1.4) you can create a polyMesh for OpenFOAM and
you can visualize the results. The program is GNU-software and is a part of the
CalculiX package. Please see the CalculiX home-page at www.calculix.de.

For the moment only 8 noded bricks are supported. You can use mesh-grading and
opposide faces of a meshed block might use differend element densities (ie. you
can go from 10 elements at the bottom to 6 at top and from 4 left to 12 right
etc.).

Also you might create an stl file based on outer faces of a volume and mesh it
with NETGEN.

Here are a copy from the manual describing the concept:

This program uses the openGL library for visualization and the glut library
for window management and event handling.

The cgx has pre- and post-processor capabilities for FEM applications.
It is able to generate and display beam, shell and brick elements in its
linear and quadratic form. In addition it can display but not create penta-
and tetraeder-elements.

But it is possible to generate a surface-mesh of triangles and export it in
stl-format. This format can be read by an external mesher as for example
NETGEN. This mesher fills the volume with tetraeder elements and is able to
export abaqus format. This can be read by cgx and ccx.

The inbuild mesher creates a structured mesh based on a description of the
geometry. For example it uses lines for beam elements, surfaces for shell
elements and volumes (bodies) for brick elements. The program distinguishes
between the mesh and the underlying geometry. Elements are made from faces
and faces are made from nodes. If you move a node the faces and elements will
folow. The geometry behaves accordingly to the mesh:
Lines are made from points, surfaces are made from lines and bodies are made
of surfaces. Surfaces might have 3 to 5 edges and bodies might have 5 to 7
surfaces. As a result of the concept, if you modify the position of a point,
all related geomety will follow. In other words, if the location of geometric
entities should be changed, it is necessary to move the points on which the
entities rely.

It should be noted that faces exist only on free surfaces of the model.

In addition entities called "set" are available to group together whatever
entities. Sets are useful to handle parts of the model. For example to
manipulate or display this parts. After the mesh is created it must be written
to a file to be available for the solver. Also several boundary conditions and
loads can be written to files. This files have to be added into the ccx
control file. Additional commands as the type of analysis, material
description and so on must be added with the help of an editor. After the
analysis is completed the results can be visualized by calling the cgx program
again in an independent session. The post-processor functionality is mainly
controlled by a pop-up menu were the pre-processor functionality is controlled
by the keyboard. Shaded animations of static and dynamic results, the common
color plots and time history plots can be created. Also a userfunction can be
included. For example if someone needs his own functions to manipulate the
result-data of a calculation or if he needs an interface to read or write his
own format of result-data.

Greetings,
Klaus

[hsieh]

Hi, Klaus,

Thanks for the great work!

Can you give a brief description of steps how to generate OpenFOAM meshes using cgx? Is it possible to use cgx to setup BCs (or maybe just setup the boundry face names and then use these names later with foamX)? It might be great if we can use cgx as a pre-processor for OpenFOAM.

pei

[klaus]

Hello Pei-Ying,

thanks for the flowers

You generate points either by typing commands in cgx or by reading a initial file (you can also import a cad geometry if you can produce vda format). Then you create some lines and surfaces. Then you should use the swep command to extrude in the 3th dimension. Then you define he8 (8 noded brick) elements and you mesh the structure. Then you use the send command to write the mesh in foam format. Before you define some sets which you will use as patches for your boundary conditions. Please look in the manual and the tutorial for more details (command: send , read and section Tips and Hints-> foam)

Best,
Klaus

[hsieh]

Hi, Klaus,

I colud not find a Calculix forum. So, hopfuly, it is ok to post this Calculix question here.

I installed the binary version (cgx 1.4) on two Fedora Core 3 (32 bit) systems and one Fedora Core 4-x86_64 system. I followed the tutorial, on all 3 systems, after I entered "plot m all" (the two steps before this were "elty all he8" and "mesh all" - both no problem), system closed cgx and log me out (go back to the log in screen).

Has it occurred before? Do you know how to fix this? Thanks a lot!

Best,

pei

[klaus]

Hello OpenFoam friends,

i made corrections to the binary and source-code of cgx:
- sometimes elements in the presentation of OpenFOAM results were
twisted. I corrected this.
- if no boundary patches were specified for writing OpenFOAM meshes a
segfauld happened. I also corrected this.
- the orig glut-library is now in the source. This is a better
interfaces than the usually installed free-glut.

The internal version-number has canged from 1.4 to 1.4.1 but the
file-names are unchanged.

Best,
Klaus

[nandita]

Hello Friends,

I got from calculix forum that with the help of Blender CAD files can be translated to . fbd format and hence can be meshed with help of calculix . But I am not familiar with blender so how should operate blender so that I will get all components(shapes/sub-shape) in case of solid so that i will able to export . fbd format without any lose of information it contain.please Explain me the steps clearly to treat a solid part with blender and then export to .fbd file format and perform meshing with caluculix.

Actually while I am exporting solid , at calculix window I am just able to get points and line not the whole solid and all feature it contains


Please help me in this regard!


Thanks in advance
Nandita Dash
S/W Developer

[gdbaldw]

Nandita,

Blender has very rich documentation, a large and active online community, and very helpful forums.

After learning Blender through those sources, the export tool will be useful to you.

A revision of the tool is posted at
Forum post

Doug