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Could I use a COMSOL eigenfrequency mode result as initial value of a time dependent simulation?

Posted 13 nov. 2016, 04:48 UTC−5 MEMS & Nanotechnology, Acoustics & Vibrations, MEMS & Piezoelectric Devices, Structural Mechanics Version 4.3a 2 Replies

Qi Zhang
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I want to calculate strain energy of a system, say a single beam, with deformation being coupling of two modes. Taking single beam system with dimension 1*1*100 um as an example, set the two ends of the are fixed and we will find all mechanical eigenmodes (shapes are sinusoidal) by eigenfrequency study in structural mechanics. Now i am trying to calculate total strain energy of the beam when the beam is deformed in shape of the superposition of first two modes with coefficients q1 and q2 respectively. One way to realize this is that output the shape of the first two modes and sum the shapes multiplying by q1 and q2 respectively, then input the result as a initial value in a time dependent study.
Can this be done?
P. S. Apparently the two studies should be in same mesh.
P. S. 2 Now I can output the mode shape as a .txt document, but this may not be able input to comsol again.
2 Replies Last Post 16 nov. 2016, 21:49 UTC−5
Henrik Sönnerlind COMSOL Employee

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Posted: 8 years ago 14 nov. 2016, 07:42 UTC−5
Hi,

You could use an expression like

q1*withsol('sol2',u,setind(lambda,1))+q2*withsol('sol2',u,setind(lambda,2))

Regards,
Henrik
Hi, You could use an expression like q1*withsol('sol2',u,setind(lambda,1))+q2*withsol('sol2',u,setind(lambda,2)) Regards, Henrik
Qi Zhang
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Posted: 8 years ago 16 nov. 2016, 21:49 UTC−5
Thank you very much for your reply!

But I still cannot get it to work. It seems that the withsol operator comes from version 5.1 of COMSOL, but what I am using is version 4.3a. Are there any alternative method to do this?

Thanks very much in advance.
ZHANG, Qi
Thank you very much for your reply! But I still cannot get it to work. It seems that the withsol operator comes from version 5.1 of COMSOL, but what I am using is version 4.3a. Are there any alternative method to do this? Thanks very much in advance. ZHANG, Qi

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