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Dynamic CNT Cantilever Beam

Posted Feb 2, 2011, 5:05 p.m. EST MEMS & Nanotechnology, MEMS & Piezoelectric Devices Version 5.0, Version 5.2, Version 5.2a 5 Replies

Gilbert Canon
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Hi,

I'm currently working on a dynamic model for (initially) a 2D CNT cantilever beam. I already solved the static problem as in the Solid Mechanics example at Comsol. However, now I'm including the time dependent terms at the Linear Elastic Material equation; which becomes a damping problem of the form md^2w/dt^2+cdw/dt+EId^nw/dx^n=something, where w is the deflection. My question is, when comsol solves the time-dependent study, does it consider the term which depends on distance as well, I mean, do I have to run first an stationary study and then a time-dep. study? I'm asking this cause I solved the dynamic model and It works, however there is a huge gap between the Pull-in voltage that I obtained with the stat. study and the one with the time dep.(ther should be a gap, but not of this proportions) study. So, the point is I want to know if the problem is at solving or if I took a wrong damping constant or something. By the way, I've read that the rayleigh damping is more suitable for this kind of problems, but when I use that damping I get almost no movement, so I opted for the loss isothropic damping and It works quite well. If someone can help me clarify these issues I would be very grateful.

Thank You

I'm using Comsol 4.0a
5 Replies Last Post Oct 10, 2016, 10:14 p.m. EDT
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Hello Gilbert Canon

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Fiheon Imroze
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Posted: 1 decade ago Nov 23, 2014, 9:11 p.m. EST
How to get CNT in comsol I have searched in the material library
How to get CNT in comsol I have searched in the material library
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Nov 25, 2014, 2:17 a.m. EST
Hi

Sorry but what do you mean by CNT ?

Acronyms are not universal, particularly not across the language barriers, and here on the Forum we represent roughly all the world and all languages :)

is it CNT = Carbon Nano-Tubes ?

if so, you need to decide if you are doing molecular FEM or work withlinear continuous material hypotheses FEM.
In the former case I do not believe COMSOL is ready yet (no specific module for that physics yet), then you must write out the atom interaction yourself.
If its the second case, your issue, from my understanding, is to identify correct material properties for the "bulk" CNT if that can be named like that.
But those values are not in my material list so I cannot help any further

--
Good luck
Ivar
Hi Sorry but what do you mean by CNT ? Acronyms are not universal, particularly not across the language barriers, and here on the Forum we represent roughly all the world and all languages :) is it CNT = Carbon Nano-Tubes ? if so, you need to decide if you are doing molecular FEM or work withlinear continuous material hypotheses FEM. In the former case I do not believe COMSOL is ready yet (no specific module for that physics yet), then you must write out the atom interaction yourself. If its the second case, your issue, from my understanding, is to identify correct material properties for the "bulk" CNT if that can be named like that. But those values are not in my material list so I cannot help any further -- Good luck Ivar
Fiheon Imroze
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Posted: 1 decade ago Nov 25, 2014, 5:54 a.m. EST
I have read papers in which people have simulated carbon nanotube field emission I also want to achieve the same goal.
I have read papers in which people have simulated carbon nanotube field emission I also want to achieve the same goal.
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago Nov 25, 2014, 1:49 p.m. EST
Regarding the original question, the pull-in voltage should not depend on whether the analysis is stationary or time dependent, assuming that voltage is applied over a sufficient time period. Also, isotropic damping does not work in a time dependent study. It is only used in frequency domain studies. The Rayleigh damping you included may have been too high. Check the COMSOL documentation for guidelines on selecting the two Rayleigh damping coefficients.

Nagi Elabbasi
Veryst Engineering
Regarding the original question, the pull-in voltage should not depend on whether the analysis is stationary or time dependent, assuming that voltage is applied over a sufficient time period. Also, isotropic damping does not work in a time dependent study. It is only used in frequency domain studies. The Rayleigh damping you included may have been too high. Check the COMSOL documentation for guidelines on selecting the two Rayleigh damping coefficients. Nagi Elabbasi Veryst Engineering
Srivathsava Surabhi
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Posted: 8 years ago Oct 10, 2016, 10:14 p.m. EDT
Dear Ivar,

I would like to know that, at present, if there is any model available on carbon nanotubes (CNT) in which the electric field or magnetic field distribution is investigated in and around the CNT and other electromagnetic based characteristics, on either non-uniform or uniformly oriented CNT papers or both of them. In my search, I found the attached paper in Comsol website whose investigation is a different purpose. Anyway, there are no much models available as per my search, so I am seeking your suggestion.

Thanks in advance.

Srivathsava Surabhi
Dear Ivar, I would like to know that, at present, if there is any model available on carbon nanotubes (CNT) in which the electric field or magnetic field distribution is investigated in and around the CNT and other electromagnetic based characteristics, on either non-uniform or uniformly oriented CNT papers or both of them. In my search, I found the attached paper in Comsol website whose investigation is a different purpose. Anyway, there are no much models available as per my search, so I am seeking your suggestion. Thanks in advance. Srivathsava Surabhi

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