Unstructured mesh - element selection

Dear FEFLOW users,

I have a layered feflow model that should by improved by the incorporation of some extra 3d geometries (tunnel). The tunnnel is 3d, not represented with a line. To do that improvement I've used tetgen to refine the mesh in some subsections of the model (where the tunnel is located). So, remeshing worked perfectly, nice work. Just after meshing two extra options turned up in the selection panel: node and face selection along the tunnel. Great, both of them work brilliantly (Fig1). BUT I could not make element selection along the tunnel. I've tried to convert face/node selection to element selection, but this conversion resulted in some extra element selection beyond the outer faces of the tunnel (Fig2).

I speculate that face/node selection conversion to element selection considers all elements that are in contact with face/node selection. I mean, for instance, a node on the surface of my tunnel is shared by several elements, some of them is within the tunnel, but some of them is out of the contour of the tunnel (in the rock). I'm not 100% sure about this...just a speculation.

Anyway, I have a question: is there any way to have appropriate element selection? I need only the elements which build up my tunnel, no interest in "rock" elements

Thanks,

Kalman

If the top and bottom of the tunnel have the same lateral spatial extend (top and bottom polygon are the same) I may have a possible solution. It’s a bit tricky, but it should work in principle.

In FEFLOW Export the centroids as a shapefile from the elements by exporting a material property. Use GIS to clip the points laterally. Now, you should have the points which are laterally located within the tunnel. However, you still have points which are located above and below the tunnel.

To identify these points please also use GIS to make a TIN (Triangulated Irregular Network) for the top and for the base of the tunnel. Write the elevations of both TIN’s at the XY-location for each point in the attribute table of the point-shapefile. The function Add Surface Information may help you: http://pro.arcgis.com/en/pro-app/tool-reference/3d-analyst/add-surface-information.htm
Finally, you have three columns with elevations of interest for each point you previously exported from FEFLOW. Top and bottom elevation of the tunnels and the elevation of the point itself. Delete all points which are located either above or below the tunnel, by making simple attribute queries. All remaining points you do not deleted will be spatially located within the tunnel.

Finally, load the file in FEFLOW and make a selection in 3D. The selection settings can be adjusted in the FEFLOW Problem Settings – Map Settings – 3D selection distance settings – Select by fixed distance. Use a small number (0.1 m) in x/y/z-direction.