In the first step, the model nodes that lie within the partial model boundary are deleted from the overall model. The following figure shows the area of the partial model before importing it into the overall model..

Model area of the partial model before integration into the overall model

The nodes and elements are removed from the existing overall model along the outer edge of this model (Mesh Nodes Delete Inside structure and Mesh Element Delete Inside structure). The following figure shows the remaining mesh of the overall model.

Area of the partial model removed from the overall model (outlined in red)

In the case of concave boundary lines, elements may be retained in individual cases that lie on the surface of the submodel and must therefore be removed (elements highlighted in cyan that lie outside the red boundary line). This situation arises because all corner nodes of these elements are retained when deleting. These elements must be removed manually.

Example of elements that are not removed when the submodel area is deleted

A second step consists of checking whether linear data structures (e.g. watercourse lines) intersect the cut-out model boundary several times. If this is the case, the lines must be split between the point at which the line leaves the remaining model area and the point at which it re-enters the model area. The following figure shows such a situation. Figure (a) shows the initial situation in the overall mesh. In figure (b), the mesh was cut out along the interrupted red line. A blue line runs out of the remaining mesh and back into it at another point. The points at which such a situation occurs must be identified manually for each line-wise data type and cleaned up by separating these lines (c). This step is not only necessary for correct visualisation (e.g. markings), but also, for example, for correct consideration of the line-wise leakage boundary condition.

Correction of line data that intersect the edge of a cut-out mesh several times

Horizontal boundary adjustment