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Modeling elastic waves in a solid mechanics study

Posted Jan 9, 2013, 8:34 a.m. EST RF & Microwave Engineering, Acoustics & Vibrations, Structural Mechanics 10 Replies

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Hi,

I'd like to ask a question concerning the modeling of elastic waves in the structural mechanics module. The geometry is a simple 3D beam, free on all sides. (file attached)

My goal is to study the elastic waves propagating in the z-direction - based on the full elasticity equations. However, currectly I see no good way to implement the requirement that the displacement field is a harmonic wave with wavevector K in the z-direction (explicit requirement attached).

When I simulate the beam with all-free boundary conditions, I do get some of those waves. But now it is not easy to extract the wavevector, and I get many modes that are not such elastic waves at all.

I have thought about using periodic boundary conditions, but I still didn't find a good way to just look for those modes with wavevector K.

Any help would be greatly appreciated!

Thanks
10 Replies Last Post Jan 21, 2014, 9:44 a.m. EST
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago Jan 9, 2013, 12:15 p.m. EST
Try setting the type of periodicity in the periodic BC to “Floquet Periodicity”.

Nagi Elabbasi
Veryst Engineering
Try setting the type of periodicity in the periodic BC to “Floquet Periodicity”. Nagi Elabbasi Veryst Engineering
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Posted: 1 decade ago Jan 9, 2013, 2:36 p.m. EST
Hi Nagi,

thanks for your quick reply. Unfortunately, there is no such option in the 'periodicity type' menu. I can only choose between 'continuity' and 'antiperiodicity'.

Any other ideas?

Thanks again!
Hi Nagi, thanks for your quick reply. Unfortunately, there is no such option in the 'periodicity type' menu. I can only choose between 'continuity' and 'antiperiodicity'. Any other ideas? Thanks again!
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago Jan 9, 2013, 2:42 p.m. EST
Make sure you’re looking at the top “Type of periodicity” tab (see attachment). If you still don’t see the Floquet Periodicity option then you may be using an older COMSOL version. I believe this feature was introduced in v4.3.

Nagi Elabbasi
Veryst Engineering
Make sure you’re looking at the top “Type of periodicity” tab (see attachment). If you still don’t see the Floquet Periodicity option then you may be using an older COMSOL version. I believe this feature was introduced in v4.3. Nagi Elabbasi Veryst Engineering

Attachments:

Hassanain Al-Taiy
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Posted: 1 decade ago Jan 16, 2013, 9:43 a.m. EST
Dear All

i hope that you are well

i try to make a simulation of modal coupling between optical and elastic modes in silicon waveguide, i get the optical modes, but the elastic mode not yet.

my questions are how to make the coupling between the optical and elastic modes to get the final mode and how can i calculate the radiation pressure and electrostriction force in this model.


Best Regards to the all.


Hassanain
Dear All i hope that you are well i try to make a simulation of modal coupling between optical and elastic modes in silicon waveguide, i get the optical modes, but the elastic mode not yet. my questions are how to make the coupling between the optical and elastic modes to get the final mode and how can i calculate the radiation pressure and electrostriction force in this model. Best Regards to the all. Hassanain
Dennis Liu
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Posted: 1 decade ago Jan 16, 2014, 10:22 a.m. EST
Hi Hassanain,

I am also making an attempt to couple optical and acoustic modes in a wave guide but having troubles doing so. Are you simulating in a 2D or 3D structure?

Thanks

Dennis
Hi Hassanain, I am also making an attempt to couple optical and acoustic modes in a wave guide but having troubles doing so. Are you simulating in a 2D or 3D structure? Thanks Dennis
Hassanain Al-Taiy
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Posted: 1 decade ago Jan 17, 2014, 4:41 a.m. EST
I am simulating in 3D.

--
Best Regards

Hassanain
I am simulating in 3D. -- Best Regards Hassanain
Dennis Liu
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Posted: 1 decade ago Jan 20, 2014, 2:46 p.m. EST
Hi Hassanain,

Did you have any success coupling optical and elastic modes?
If so, did you have 2 separate studies for optical and elastic, or did you have different study steps (eigenfrequency and optical mode analysis) in order to couple two physics.

I am a beginner and attempting to learn COMSOL, any guidance you can provide will be a great help.
If you still happen to have your model, that would be a great help too.

Regards,
Dennis
Hi Hassanain, Did you have any success coupling optical and elastic modes? If so, did you have 2 separate studies for optical and elastic, or did you have different study steps (eigenfrequency and optical mode analysis) in order to couple two physics. I am a beginner and attempting to learn COMSOL, any guidance you can provide will be a great help. If you still happen to have your model, that would be a great help too. Regards, Dennis
Hassanain Al-Taiy
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Posted: 1 decade ago Jan 21, 2014, 2:29 a.m. EST
Dear Denis

sorry for being late to answer since i was very busy, what i did is to simulate the optical mode (mode analysis) and elastic mode via Eigen frequency to calculate the acoustic mode displacement.


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Best Regards

Hassanain
Dear Denis sorry for being late to answer since i was very busy, what i did is to simulate the optical mode (mode analysis) and elastic mode via Eigen frequency to calculate the acoustic mode displacement. -- Best Regards Hassanain
Hassanain Al-Taiy
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Posted: 1 decade ago Jan 21, 2014, 2:29 a.m. EST
Dear Denis

sorry for being late to answer since i was very busy, what i did is to simulate the optical mode (mode analysis) and elastic mode via Eigen frequency to calculate the acoustic mode displacement.


--
Best Regards

Hassanain
Dear Denis sorry for being late to answer since i was very busy, what i did is to simulate the optical mode (mode analysis) and elastic mode via Eigen frequency to calculate the acoustic mode displacement. -- Best Regards Hassanain
Dennis Liu
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Posted: 1 decade ago Jan 21, 2014, 9:44 a.m. EST
Thanks alot Hassanain,

That is what I am trying to do also, I couldn't quite get a correct boundary mode analysis of a 3D optical fiber as my wave won't propagate through the fiber (it stops at the input port and fades away immediately), don't know what the problem could be.

Thanks again for you answer,
Dennis
Thanks alot Hassanain, That is what I am trying to do also, I couldn't quite get a correct boundary mode analysis of a 3D optical fiber as my wave won't propagate through the fiber (it stops at the input port and fades away immediately), don't know what the problem could be. Thanks again for you answer, Dennis

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