Boundary elements using extrude in gmsh

[Louise Olsen-Kettle]

When I use extrude for a 2D surface in gmsh to create a volume the mesh does not seem to have a boundary on the extruded surface in eScript.

I am attaching a plot of the boundary elements created using:

mydomain=ReadGmsh('meshselfsimilar.msh',3)
test_boundary=Scalar(1.,FunctionOnBoundary(mydomain))
saveVTK("Test_boundary.vtu",test_boundary=test_boundary)

Is there a way to ensure gmsh saves the boundary surfaces of the extruded volume using command Extrude in gmsh?

[Lutz Gross (l-gross)]

The top surface and potentially all other surfaces need to be added as "Physical Surface" to the geometry otherwise the surface elements are not written into the mesh file.

It should work in the follwoing way:

out[] = Extrude { ... } { };

Physical Surface("top") = { out[0] }

PS: The "out[]"- list is explained in https://fossies.org/linux/gmsh/tutorial/t3.geo

[Louise Olsen-Kettle (lokettle)]

Thanks Lutz, what happens if you tag the same surface twice with two different physical tags - is this a problem?

For example I have complex holes and filling in the mesh i'm trying to create and the same line is extruded for surfaces to create volumes that are adjacent to each other. Is this a problem?

[Lutz Gross (l-gross)]

first question: I am not so sure if this is a problem. The question is which tag is finally used.

second question: Not sure I do understand the question. I assume you want to have an internal boundary between the volumes (something like continuous displacement and normal stress)?

[Louise Olsen-Kettle (lokettle)]

Thanks Lutz, I have solved it and what I thought was a problem is not a problem. Sorry for that.