As the mesh of a partial model is usually refined for detailed questions, the boundary nodes between the partial and overall model must be adapted. For this purpose, the boundary nodes of the partial model are reduced to the boundary nodes of the overall model. The advantage of this procedure is that either triangular elements are created from quadrilateral elements or elements are omitted completely. In this case, there is no need to create a new element, which would then also have to be re-parameterised. The following figure illustrates this work step:

Adjusting the boundary nodes of the partial and complete model

Figure (a) shows the elements of the refined partial model in black and the elements of the existing overall model in red. The blue line marks the outer edge of the partial model, i.e. the seam line of the two meshes to be merged. The red dots mark those refined edge nodes of the sub-mesh that have no equivalent in the overall mesh. These nodes must therefore be eliminated before the two meshes are integrated. Simply deleting these nodes does not make sense, as the neighbouring elements are also deleted. SPRING supports the manual moving of nodes to neighbouring nodes (red arrow). In the menu sequence Mesh Nodes Merge Pick two, one of the two nodes and any elements that may be deleted are automatically removed. Image (b) shows the cleaned-up mesh.

In this step, care must be taken to ensure that no unfavourable element geometries for the numerical calculation occur or that no impermissible elements remain (see figure).

Example of the creation of impermissible elements during the reduction of edge nodes

These relationships must be observed for each individual node when merging. In cases with very few individual occurences, if both possible shift directions lead to inadmissible elements, manual shifting of individual mesh nodes inside the model or splitting of quadrilateral elements is unavoidable.

Remark:

To avoid this work step, it is generally recommended to avoid mesh refinement at the edge nodes both horizontally and vertically!

Vertical boundary adjustment