Help a novice to solve a simple liquid-in-solid problem

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mspock
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Help a novice to solve a simple liquid-in-solid problem

Post by mspock »

Hi everybody.
I'm totally new to Elmer at the moment. It's been only for a few days that I'm trying to understand the basis.
I'm using GID as mesher but maybe I'm driving to another one in the future.
I'm using ThinkDesign as 3d environment.

Project: I'd like to study the thermal flow in a solid cooled by a water pipe.

what I do:
- export in stp, stl, igs formats. For example, the solids I export are 1) a cube with an hole 2) a cylinder representing water. The cylinder is exactly matching the hole in the cube.
- import in GID the solids: cube in layer 0 and tube in layer 1 (although I suppose Gid has a bug here, importing only to layer 1 so one has to move objects to other layers in order to prevent them to be overwritten).
- adjust the surfaces and volumes to make 2 separate solids: cube with hole and tube the external surface of the tube and the hole surface should now collapse or not? Should I mantain one surface only?
- meshing: 3d or 2d? In the curved pipe example, 2d mesh is used.
- problem type: elmer -> set data, materials, volumes. My goal is to assign a material (ie steel) to body and another one (ie water) to the cooling liquid. Thanks to different layer I succeed to assign them.
- problem type: elmer -> set data, costraints, surfaces: I assign costraints according my wanted boundaries: 1) steel body (all surfaces but the inner hole one) 2) cube inner hole surface 3) one base of the cilynder 4) the other base surface 5) the lateral cilynder surface : total of 5 costraints. Is it correct?
- save project and calculate
- importing in Elmer: open mesh--> select folder of previoously calculated Gid problem
- elmer crashes. Either does crash importing the 2 solids having a common surface, or it does import only one solid, even if I exported both by GID.

Have you guys some advice/tutorials/step by step guide to import a geometry consisting of a solid with a hole in which i can make a liquid flow to refrigerate it?
I can't just understand where am I wrong !!

Thank you so much.
mzenker
Posts: 1999
Joined: 07 Dec 2009, 11:49
Location: Germany

Re: Help a novice to solve a simple liquid-in-solid problem

Post by mzenker »

Hi,
adjust the surfaces and volumes to make 2 separate solids: cube with hole and tube the external surface of the tube and the hole surface should now collapse or not? Should I mantain one surface only?
there must be only one surface between the bodies, otherwise you will get a nonconformal mesh at the interface and no heat will flow between the bodies.

2D or 3D: this depends on the nature of your problem.

GiD -> Elmer: there is a page for this on the Elmer Wiki.

You can find tutorials on the documentation page.

HTH,

Matthias

Remark: I think this thread can be moved to the "ElmerSolver" or "External Tools" forum.
mspock
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Re: Help a novice to solve a simple liquid-in-solid problem

Post by mspock »

Thank you very much Matthias,
I've read the guides and tutorial /examples, however there are many questions which I can't find an answer to.
I know how to set an "elmer problem" in gid, but either i can't set the right boundaries, or I can't succeed to have a solid formed by 2 other solids, all meshed up.
For each format I've tried, I found a different problem / troubles ( ie geometry, import, export, meshing, ....and so on)
As my geometry is very simple ( You can find it either here attached, or finally in the right place where i moved my question in this forum ) , I gently ask if anyone can try to mesh the solids with imposing the right boundaries.
Thank you for your help.
Attachments
2 solids.zip
(7.18 KiB) Downloaded 434 times
mzenker
Posts: 1999
Joined: 07 Dec 2009, 11:49
Location: Germany

Re: Help a novice to solve a simple liquid-in-solid problem

Post by mzenker »

Hi,

meshing your geometry is not so difficult, you can do it yourself.
I don't know GiD well enough to tell you how to do it with GiD. I use gmsh, and would proceed as follows:.

* import "hollow plate.igs"
* save as .geo
* define the plate as volume (as far as I see, there is no volume defined so far)
* define circular planes at both ends so that the hole is closed
* define a second volume using the newly defined planes and the tubular inner surface of the hollow plate
* set the max element size (options->mesh) to something reasonable
* make a 3D mesh
* save in .msh format
* open with ElmerGUI

A similar workflow is certainly possible with GiD or other meshers.
If you merge both files, you have to resolve the duplicated interface somehow. I think GiD can do that in many cases - for more info, you have to ask someone who knows GiD (there is a mailing list).

HTH,

Matthias
mspock
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Re: Help a novice to solve a simple liquid-in-solid problem

Post by mspock »

Matthias,
thanks for your answer. That was one of my trials (both in Salome and in GID). I'll try gmsh too.
GID gives me a meshed solid but Elmer doesn't recognize it (yep I have saved it as an elmer problem)
SALOME can't just make a volume selecting the contour: I have to construct edges/wires and to cap them with a surface. This method is however approximate and gives me a bad surface / bad internal solid.
Also merging the files and taking away the duplicate surfaces does result in an unreadable elmer problem.
Thank you for your patience, I'll try to make one of them work and will report back.
mzenker
Posts: 1999
Joined: 07 Dec 2009, 11:49
Location: Germany

Re: Help a novice to solve a simple liquid-in-solid problem

Post by mzenker »

Hi,

did you try to seek assistance on the GiD mailing list?
I have tried GiD shortly some time ago. The guy who provides user support needs sometimes some days to respond, but he does.

Good luck,

Matthias
raback
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Re: Help a novice to solve a simple liquid-in-solid problem

Post by raback »

Hi mspock

Note that if you save the mesh already in Elmer format you should use "Load mesh" in ElmerGUI whereas all other mesh formats are associated with "Open".

-Peter
mspock
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Re: Help a novice to solve a simple liquid-in-solid problem

Post by mspock »

@ Matthias, not yet, but I will for sure. I was looking for a completely GNU method however. I'll try GMSH soon.
@ Peter: thanks, I'm aware of that. It is maybe due to the windows programs versions? Hope not.

It's unbelieveable that I've encountered so many problems with this simple geometry, and I have'nt even begun to use solver :( . Loosing my mind on that:

- importing geometry (IGES or STEP) to GID or SALOME
- capping with plane surfaces
- creating a new "internal=water" volume is simple in GID, is quite complicated in SALOME (deleting overlapping surfaces)
- boundaries in GID are simple to impose. In Salome...well...i have to put my mind on that (using groups maybe?).
- importing in Elmer once meshed
- either Elmer crashes, or does not displays my geometry/mesh.


Thanks guys for your patience. I know It should be a very simple and stupid thing, I'm simply a novice ;)
raback
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Re: Help a novice to solve a simple liquid-in-solid problem

Post by raback »

Hi

The OS workflows are not that well streamlined. Therefore when starting with simple problems I would suggest using a rather short workflow. If you look what people usually use for mesh generation you'll see that gmsh is rather popular. See:
viewtopic.php?f=9&t=2023
There you can also do simple geometry generation eliminating the possible problems with the CAD geometries.

-Peter
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