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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 The information provided may be out of date.

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Geometry Units and Convergecne

Posted 2014年7月24日 GMT-4 02:27 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 2014年8月7日 GMT-4 08:19
Jeff Hiller COMSOL Employee

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Posted: 1 decade ago 2014年7月28日 GMT-4 10:37
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 2014年8月6日 GMT-4 22:31

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 2014年8月7日 GMT-4 08:19
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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