How to get the internal part of a tube

[Sedullo]

I have a cad geometry which is similar to a tube, my goal is to simulate a fluid inside this "tube".

I would like to create a "negative" of this geometry, basically I would like to create a cad of the fluid part. If you think about a straight tube, I would like to get a cad of the internal cylinder inside the tube.

Is that somehow possible?

The next step will be to create the stl of this negative and make a mesh out of it using snappyhexmesh in OpenFOAM.

[thschrader]

Do you mean something like this?
A hollow pipe in a block. You want to simulate the flow through
the pipe, but there is nothing to mesh. Because the pipe is hollow…

pipe.JPG (31.65 KiB) Viewed 5437 times

[RatonLaveur]

Well, why don't you simply build a solid cylinder representing the actual fluid volume?

In CFD in FreeCAD there are really two ways to create the domain:

A. The domain is simple enough that you can recreate it in positive.

B. You have an existing part with complex cavities, in which case you can use that existing part to carve out from a solid volume (boolean operation).

[polymer]

Maybe a function for creating a part from the inner Volumen could be added to FreeCad.
Two steps: first select faces of the entry/outlet, then select a face of the inner volume.

For example:

phpBB [video]

[thschrader]

Maybe a function for creating a part from the inner Volumen could be added to FreeCad.
...

You can use the defeaturing/curves wb.

fill_hole_and_mesh.JPG (103.09 KiB) Viewed 5275 times

[RatonLaveur]

You can use the defeaturing/curves wb.

ah...that is a great idea, let me suggest a little further: what if only the "necessary" tools of that workbench were integrated in the CfdOF//FEM module as a set of "Model preparation" tools ? Which would become a first step in the workflow for simulating in FreeCAD.

[thschrader]

You can use the defeaturing/curves wb.

ah...that is a great idea, let me suggest a little further: what if only the "necessary" tools of that workbench were integrated in the CfdOF//FEM module as a set of "Model preparation" tools ? Which would become a first step in the workflow for simulating in FreeCAD.

You can arrange your tools with "Tools/customize".
But I have never used this option, I can live with the actual workbench structure.

Tools_customize.JPG (39.78 KiB) Viewed 5190 times

[polymer]

Maybe a function for creating a part from the inner Volumen could be added to FreeCad.
...

You can use the defeaturing/curves wb.
fill_hole_and_mesh.JPG

That is right and will be a quick and easy method for simple geometries like the given example. But due to partly uncomfortable usability regarding selecting inner or hidden geometries, an automatism would be helpful. See the other topic with the vacuum cleaner in the German sub-forum.

[RatonLaveur]

as far as I know, there's a lot of development by user realthunder regarding the selection of hidden and inner faces.
https://forum.freecadweb.org/viewtopic. ... 2&start=20

[DeepSOIC]

My approach would be:
1. make a solid block that covers most of the tube, and leaves small protrusions of the ends of the pipework.
2. Part Cut the block with the tube
3. Part Explode and delete the block part. The fluid will remain.