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Thermoelastic (TED) Dissipation in Clamped-Clamped Beam. 2D and 3D don't match.

Posted Dec 11, 2015, 7:04 p.m. EST MEMS & Nanotechnology, Heat Transfer & Phase Change, MEMS & Piezoelectric Devices, Materials, Mesh, Modeling Tools & Definitions, Parameters, Variables, & Functions, Structural Mechanics Version 5.0, Version 5.1, Version 5.2 2 Replies

Dustin Gerrard
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Hello,

I am using COMSOL 5.0 to model Q_TED in a Clamped-Clamped Beam for MEMS applications. I use the same parameters in 2D and 3D model and get different results. I get Q_TED (te.Q_eig) equal to 5.5k in the 2D model and I get Q_TED 8.5k in the 3D case. I have refined the mesh (manually very fine!) and I still get the disagreement between 2D and 3D models.

Furthermore, for a simple beam the Q_TED according to Zener's theory should be around 10k. Why are these models inconsistent and don't agree with the Zener model?

I attached the files.

Thanks in advance.
2 Replies Last Post Dec 14, 2015, 11:21 a.m. EST
Dustin Gerrard
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Posted: 9 years ago Dec 12, 2015, 12:57 a.m. EST
I found this very useful model. When I changed the ends of the beam to "zero temperature deviation" the result matched in the 3D model but the 2D model is still off. What is the issue?

www.comsol.com/model/thermoelastic-damping-in-a-mems-resonator-1439d
I found this very useful model. When I changed the ends of the beam to "zero temperature deviation" the result matched in the 3D model but the 2D model is still off. What is the issue? https://www.comsol.com/model/thermoelastic-damping-in-a-mems-resonator-1439d
Henrik Sönnerlind COMSOL Employee

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Posted: 9 years ago Dec 14, 2015, 11:21 a.m. EST
Hi,

In 2D. you must choose whether to use a Plane Stress or a Plane Strain assumption. Neither of them will perfectly match the 3D results due to end effects, but Plane Stress will be closer when the 3D model is free in the third direction.

Regards,
Henrik
Hi, In 2D. you must choose whether to use a Plane Stress or a Plane Strain assumption. Neither of them will perfectly match the 3D results due to end effects, but Plane Stress will be closer when the 3D model is free in the third direction. Regards, Henrik

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