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Geometry Units and Convergecne

Posted 24 juil. 2014, 02:27 UTC−4 Computational Fluid Dynamics (CFD), Geometry, Mesh, Studies & Solvers Version 4.2 3 Replies

AR Vasel
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Hello,

Does anyone know why changing the "geometry unit" raises convergence issues? For instance, when I change mm to cm, while all other parameters are the same, simulation diverges!

Thank you in advance for your time and consideration!

AR
3 Replies Last Post 7 août 2014, 08:19 UTC−4
Jeff Hiller COMSOL Employee

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Posted: 1 decade ago 28 juil. 2014, 10:37 UTC−4
Hi Ahmedreza,
It's hard to say specifically without any information about what you're modeling, but certainly the solution of a given problem can be quite different at one scale from what it is at a different scale. For instance, by making your geometry 10 times larger you may transform a laminar flow into a turbulent one. In an EM problem, a mesh that was able to capture a skin layer at one scale may not capture it once the geometry has gone up tenfold. Etc...
Jeff
Hi Ahmedreza, It's hard to say specifically without any information about what you're modeling, but certainly the solution of a given problem can be quite different at one scale from what it is at a different scale. For instance, by making your geometry 10 times larger you may transform a laminar flow into a turbulent one. In an EM problem, a mesh that was able to capture a skin layer at one scale may not capture it once the geometry has gone up tenfold. Etc... Jeff
AR Vasel
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Posted: 1 decade ago 6 août 2014, 22:31 UTC−4

Hi Ahmedreza,
It's hard to say specifically without any information about what you're modeling, but certainly the solution of a given problem can be quite different at one scale from what it is at a different scale. For instance, by making your geometry 10 times larger you may transform a laminar flow into a turbulent one. In an EM problem, a mesh that was able to capture a skin layer at one scale may not capture it once the geometry has gone up tenfold. Etc...
Jeff


Hello Jeff,

Thanks a lot for your comment. You are absolutely right, but by scaling down the free stream velocity, I do not let the flow transfer to turbulent regime; I am pretty sure it is still laminar. Actually, I am modeling a fluid-structure interaction problem. Should I post the model here please let me know. Or I can email it to you.

I really appreciate your help.

Sincerely,
AR

--
AR
[QUOTE] Hi Ahmedreza, It's hard to say specifically without any information about what you're modeling, but certainly the solution of a given problem can be quite different at one scale from what it is at a different scale. For instance, by making your geometry 10 times larger you may transform a laminar flow into a turbulent one. In an EM problem, a mesh that was able to capture a skin layer at one scale may not capture it once the geometry has gone up tenfold. Etc... Jeff [/QUOTE] Hello Jeff, Thanks a lot for your comment. You are absolutely right, but by scaling down the free stream velocity, I do not let the flow transfer to turbulent regime; I am pretty sure it is still laminar. Actually, I am modeling a fluid-structure interaction problem. Should I post the model here please let me know. Or I can email it to you. I really appreciate your help. Sincerely, AR -- AR
Jeff Hiller COMSOL Employee

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Posted: 1 decade ago 7 août 2014, 08:19 UTC−4
Feel free to contact COMSOL's technical support to request assistance if your license is eligible for that service: www.comsol.com/support/
Best,
Jeff
Feel free to contact COMSOL's technical support to request assistance if your license is eligible for that service: www.comsol.com/support/ Best, Jeff

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