2. Preprocessing
Here is a little java animation which shows how to build a finite-element mesh for a tunnel in urban environment.
An object-oriented approach is adopted for mesh generation. The key feature of the approach, data encapsulation, leads to a user friendly strongly modular, and fully windows compatible organization of the preprocessing, which is illustrated in figure 2.1.
Fig. 2.1 - The preprocessing user interface
The access to a specific object is done through a mouseclick on the object, element 1 here in the figures; pointing on an object will automatically activate the list box giving access to the methods corresponding to tasks that the selected object can perform.The association of a specific material with the element is one of these tasks and can be activated at this point.
The whole preprocessing is therefore restricted to a non sequential series of object selections by a mouseclick, followed by the activation of the appropriate method.
The user friendliness and the effciency of the approach is illustrated in figures 2.2.1 to 2.2.7 in an example of meshing a tunnel in an urban area. Experience shows that typical finite element meshes of e.g 1000 elements can easily be generated in 15 to 30 minutes.
Fig. 2.2.1 - Problem geometry
Fig. 2.2.2 - Creation of a circular tunnel, with semi-automatic meshing
Fig. 2.2.3 - Homothetical expansions to modelize the tunnel lining and the frozen zone
Fig. 2.2.4 - Creation of the prospection shaft
Fig. 2.2.5 - Mesh around the holes (semi-automatic)
Fig. 2.2.6 - Final mesh with material definition, loads and boundary conditions
Fig. 2.2.7 - Water pressure and seepage surface elements definition