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# Concept

This program uses the openGL library for visualization and the glut library [2] for window management and event handling. This results in very high speed if a hardware-accellerated openGL-library is available and still high speed for software-rendering (MesaGL,[1]).

The cgx has pre- and post-processor capabilities. 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 [4]. 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 follow. 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.

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