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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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Problem: Cylinder appears to be block

Posted 28.08.2013, 07:54 GMT-4 Geometry Version 4.2a 4 Replies

Fabian Holz
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I am quite new to this program and I tried to do create a 3D circular duct.

I selected Cylinder and chose a radius of 0.004 m. In case of a short height compared to the radius, the cylinder keeps its shape in the graphics window. But when I select my desired height of 2.6 m the shape of th cylinder turns into a block! I found out that, the more the height/radius ratio is increasing, the less round the profile becomes.

Is this because COMSOL can't simulate this profile? Or is it just a bug?

I need to create a 3D object, because it appears that COMSOL does not give a correct solution using a rotated 2D object..

Thanks in advance,
Fabian

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4 Replies Last Post 29.08.2013, 03:24 GMT-4
Robert Koslover Certified Consultant
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Posted: 1 decade ago 28.08.2013, 10:00 GMT-4
I believe this is due to how Comsol Multiphysics, in coordination with OpenGL or Direct X, represents/plots 3D graphics. First of all, don't take the image on your display so literally. Remember, what actually matters is how well the mesh represents the desired geometry, not how nice the geometry's picture looks on the computer screen. Mesh your object and see if the mesh itself conforms (at least roughly) to the correct circular shape. If not, then try a finer mesh.

Another thing you can do that may help is adjust some of the graphics parameters. For example, choose Options --> Preferences --> Graphics and set Detail to Fine. This may help produce a more realistic view in the display.
I believe this is due to how Comsol Multiphysics, in coordination with OpenGL or Direct X, represents/plots 3D graphics. First of all, don't take the image on your display so literally. Remember, what actually matters is how well the mesh represents the desired geometry, not how nice the geometry's picture looks on the computer screen. Mesh your object and see if the mesh itself conforms (at least roughly) to the correct circular shape. If not, then try a finer mesh. Another thing you can do that may help is adjust some of the graphics parameters. For example, choose Options --> Preferences --> Graphics and set Detail to Fine. This may help produce a more realistic view in the display.
Fabian Holz
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Posted: 1 decade ago 28.08.2013, 10:05 GMT-4
Thank you so much for your quick and detailed answer, Robert.
Have a nice day! :)

I will give it a try now! If I am not reposting this thread, this topic is solved!
Thank you so much for your quick and detailed answer, Robert. Have a nice day! :) I will give it a try now! If I am not reposting this thread, this topic is solved!
Lasse Murtomäki
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Posted: 1 decade ago 29.08.2013, 02:44 GMT-4
You can scale your problem. Draw a low cylinder and implement a scaling factor to the height. I think I saw such an example in a tubular filter demo in the Comsol model library of an earlier version.

What is the quantity which takes an incorrect value in axial 2D symmetry? According to my experience increasing the model to 3D does not improve accuracy.
You can scale your problem. Draw a low cylinder and implement a scaling factor to the height. I think I saw such an example in a tubular filter demo in the Comsol model library of an earlier version. What is the quantity which takes an incorrect value in axial 2D symmetry? According to my experience increasing the model to 3D does not improve accuracy.
Lasse Murtomäki
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Posted: 1 decade ago 29.08.2013, 03:24 GMT-4
Look at "dialysis" in the model library. There you have the scaling example.
Look at "dialysis" in the model library. There you have the scaling example.

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