Objective: insert a dam in a topography

Starting data: level curves in DXF format and a simple model dam.gid.zip of a double curvature dam , created previously with GiD

Files->Import->DXF

and select the file topography.dxf

Lines imported from dxf

Create an auxiliary mesh to have nodes to calculate an approximated raster to represent the terrain surface

Mesh->Generate mesh...

and select default mesh size.

Now we can create the surfaces of the raster.

Create first a new layer, and set as layer to use to separate our surfaces, and then create the raster surfaces.

Geometry->Create->Geometry from mesh->Nodes to grid surfaces

set a raster cell size of 50, and select all mesh nodes

Raster surfaces

The raster is a rectangle fitting the bounding box of the selected nodes, probably the shape of squares far of data nodes is bad and does not represent anything.

Now insert the model of the dam

Files->Import->Insert GiD model...

and select the file 'dam.gid' 

Zoom near the dam

Now the dam is overlapped with the terrain, for the simulation we need to calculate the intersection with the topography.

Create a new layer and send it the surfaces near the dam, to facilitate the work, and set off unwanted layers.

Surfaces near the dam

To facilitate the intersection we will reduce the amount of surfaces to be intersected, replacing some squares by a new surface defined only by its boundary. To have a good shape it is important that the boundary is topologically a rectangle (for curves with four well defined corners)

Geometry->Edit->Join->Surfaces->Rebuild by boundary

and select the collection of surfaces of the previous image, then a new smooth NURBS surface will replace them.

And intersect the surfaces

Geometry->Edit->Intersection->Surfaces

and select the surfaces of the dam and near the dam. This will find the intersection of the curves against the surfaces, then will split the lines, then will find the intersection curves, that start and end in a point of intersection curve-surface, and will split the surfaces if possible.

Then we can delete the unwanted parts, e.g. imagine that for our simulation we don't require the surfaces under the ground.

Surfaces to be deleted in red

Geometry->Delete->Surfaces

in the contextual menu click on 'LowerEntities', to delete also its dependent lines and points

and select the red surfaces of the previous image

Final model, with the dam connected with the topography

Now the model is finished. The dam is connected with the topography, to check it draw in colors the amount of higher-entites of lines.

View->HigherEntities->Lines

Only the lines on the border must belong to 1 surface, all other lines must belong to 2 surfaces.

The level curves can be also deleted, to have only surfaces in the final model. 

Assuming that these curves are in other layers, it is possible to delete the layers and allow to delete its geometrical and mesh entities

Select in the layers window all layers except the ones of the surfaces, and press <Supr> 

Set the checkbox 'Do it for all' (to avoid the confirm question for each layer), and press the yes button.

Deleting the selected layers and its entities

And a surface mesh could be generated

Surface mesh assigning a smaller size to surfaces near the dam