In a large-scale principle model, detailed questions cannot always be managed efficiently and economically. Caused by the size of the model high computation times and the discretization are often not detailed enough.

One approach is to separate and to consider the region of interest as a partial model. The coupling of the partial model and the overall model is done by given boundary conditions, usually by mass flows. The advantages of this approach can be summarized in the following points

Large flexibility of choosing a region of interest

Mesh changes and the varying of parameters can be handled efficiently.

 

To keep the influence of the model changes on the boundary conditions low, the boundaries of the partial model should be defined far away from the region of interest. When defining the model boundary the following criteria should also be considered:

Define boundaries as far as possible along stream lines,

sufficient distance to groundwater withdrawals,

no open water areas on the boundary,

the model boundary of the partial model must be always on element edges of the overall model, there must be no quadrilateral elements cut,

the partial model area must be large enough so that changes in the transition region between partial and overall model which are usually not completely preventable during the import, have no influence on the results of the region of interest.

In order to allow a smooth import of a partial model in the overall model, the model boundary of the partial model has to remain geometrically unchanged. It may not be refined either horizontally or vertically. If this condition is not observed, the reimport requires not only additional work by the need for a boundary node cleanup, but also an interpretative effort in the case of a vertical refinement. In this case has to be determined how the refined layers are correlated with the layers of the overall model. Vertical mesh refinements, based on local needs (eg installation of sheet pile walls, tunnels, wells and locally common hydrogeologic inhomogeneities) should always be carried out only in the environment of the concerned region.

The partial model should always be calculated using the same program module as the overall model. Also the calculation parameters such as the number of iterations or the attenuation factor should be maintained.

 

Generating fractures in a 3D model <Zieltopic="Generating fractures in a 3D model", Zieldokument="Aufbau_3D.chm", ZielFenster="Main", ZielDatei="Aufbau_3D16.htm">