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Cantilever Strain at Resonance Frequencies
Posted 4 giu 2013, 12:50 GMT-4 MEMS & Piezoelectric Devices, Studies & Solvers 8 Replies
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Hello,
I am new to Comsol and am trying to simulate strain in various structures at their eigenfrequencies. I have no problem finding the eigenfrequencies, but the amplitude in the eigenfrequency study is taken to be around a meter when the cantilever or structure is on the micrometer scale. Because of this amplitude I can't use the eigenfrequency study to find strain in different resonating structures. If I could fix the total energy of the system to limit amplitudes that would be ideal.
Is there a way to limit the energy in the eigenfrequency study so that I can limit the amplitude of oscillation and have the same energys for higher order resonant frequencies? If not, how can I simulate the max strain in a cantilever or any structure vibrating at its resonant frequencies?
Thanks,
Dustin Bigham
I am new to Comsol and am trying to simulate strain in various structures at their eigenfrequencies. I have no problem finding the eigenfrequencies, but the amplitude in the eigenfrequency study is taken to be around a meter when the cantilever or structure is on the micrometer scale. Because of this amplitude I can't use the eigenfrequency study to find strain in different resonating structures. If I could fix the total energy of the system to limit amplitudes that would be ideal.
Is there a way to limit the energy in the eigenfrequency study so that I can limit the amplitude of oscillation and have the same energys for higher order resonant frequencies? If not, how can I simulate the max strain in a cantilever or any structure vibrating at its resonant frequencies?
Thanks,
Dustin Bigham
8 Replies Last Post 1 feb 2016, 01:21 GMT-5
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Posted:
1 decade ago
Hi,
The magnitude of an eigenmode is arbitrary by definition.
It is only when doing a forced response analysis including loads that amplitudes can be computed.
Regards,
Henrik
The magnitude of an eigenmode is arbitrary by definition.
It is only when doing a forced response analysis including loads that amplitudes can be computed.
Regards,
Henrik
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Posted:
1 decade ago
Hi,
I've tried applying a displacement of 1[um]*sin(2*pi*freq*t) to the free end of the diamond cantilever (200um x 10um x .3um, fixed at one end), where freq is the 2nd order frequency, and the simulation has been running for a week and is only at 34% progress... Is this the correct thing to do to simulate the 2nd order mode at 1um amplitude?
If I remember correctly my mesh is triangular with a max size of 1um, swept from the top layer to the bottom layer with a distribution of 4 or 5 layers in between.
Thanks,
Dustin
I've tried applying a displacement of 1[um]*sin(2*pi*freq*t) to the free end of the diamond cantilever (200um x 10um x .3um, fixed at one end), where freq is the 2nd order frequency, and the simulation has been running for a week and is only at 34% progress... Is this the correct thing to do to simulate the 2nd order mode at 1um amplitude?
If I remember correctly my mesh is triangular with a max size of 1um, swept from the top layer to the bottom layer with a distribution of 4 or 5 layers in between.
Thanks,
Dustin
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Posted:
1 decade ago
I've tried applying a displacement of 1[um]*sin(2*pi*freq*t) to the free end of the diamond cantilever (200um x 10um x .3um, fixed at one end), where freq is the 2nd order frequency, and the simulation has been running for a week and is only at 34% progress... Is this the correct thing to do to simulate the 2nd order mode at 1um amplitude?
If I remember correctly my mesh is triangular with a max size of 1um, swept from the top layer to the bottom layer with a distribution of 4 or 5 layers in between.
Hi,
It sounds like you should use a frequency domain analysis (possibly using the modal solver) instead of a time dependent analysis. Note also that the response you get with excitation at the natural frequency is strongly controlled by the damping that you assume.
Regards,
Henrik
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Posted:
1 decade ago
Dear comsol users,
I'm working on simulating mems rf switch ,i was able to build the structure and perform modal analysis witout biasing voltage. But can anyone help me in modeeling the beam with applied electric potential to see the desired displacement of beam at desired voltage. please reply if there's any pdf available stating the modelling of the beam displacement at given actuation voltage.
Regards
I'm working on simulating mems rf switch ,i was able to build the structure and perform modal analysis witout biasing voltage. But can anyone help me in modeeling the beam with applied electric potential to see the desired displacement of beam at desired voltage. please reply if there's any pdf available stating the modelling of the beam displacement at given actuation voltage.
Regards
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Posted:
8 years ago
Hi,
The magnitude of an eigenmode is arbitrary by definition.
It is only when doing a forced response analysis including loads that amplitudes can be computed.
Regards,
Henrik
Dear Henrik,
I'm also a new user of COMSOL and I'm trying to reproduce the results presented by ANSYS, with COMSOL's tools of Eigenfrequency Analysis.
I followed the steps suggested by bracket's example, listed in PDF paper of its tutorial, but my results have been very different of theoretical case in this website:
www.mece.ualberta.ca/tutorials/ansys/IT/Modal/Modal.html
br.comsol.com/model/download/284381/models.sme.bracket_eigenfrequency.pdf
May you help me to setup my simulation?
Thanks!
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Posted:
8 years ago
Hello ALP,
The model is attached. I ran it for 6 eigenfrequencies and with 15 elements (i.e. all default settings for the mesher and solver).
To get going with the software, we recommend you work through the two tutorials in the Introduction to COMSOL Multiphysics manual, version 5.2.
Specifically for eigenfrequency analysis of beam structures, another useful resource is the Structural Mechanics Module Verification Examples manual, version 5.2; see the "In-Plane Framework with Discrete Mass and Mass Moment of Inertia" model on page 109 and following.
All manual are accessed in the GUI through File > Help > Documentation.
Best,
Jeff
The model is attached. I ran it for 6 eigenfrequencies and with 15 elements (i.e. all default settings for the mesher and solver).
To get going with the software, we recommend you work through the two tutorials in the Introduction to COMSOL Multiphysics manual, version 5.2.
Specifically for eigenfrequency analysis of beam structures, another useful resource is the Structural Mechanics Module Verification Examples manual, version 5.2; see the "In-Plane Framework with Discrete Mass and Mass Moment of Inertia" model on page 109 and following.
All manual are accessed in the GUI through File > Help > Documentation.
Best,
Jeff
Attachments:
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Posted:
8 years ago
Hello ALP,
The model is attached. I ran it for 6 eigenfrequencies and with 15 elements (i.e. all default settings for the mesher and solver).
To get going with the software, we recommend you work through the two tutorials in the Introduction to COMSOL Multiphysics manual, version 5.2.
Specifically for eigenfrequency analysis of beam structures, another useful resource is the Structural Mechancis Module Verification Examples manual, version 5.2; see the "In-Plane Framework with Discrete Mass and Mass Moment of Inertia" model on page 109 and following.
All manual are accessed in the GUI through File > Help > Documentation.
Best,
Jeff
Thanks a lot!
Best regards.
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Posted:
8 years ago
Dear Sir,
I am simulating a capacitive micro-accelerometer in comsol. When i perform the eigenfrequency analysis, my eigenfrequencies are way different from the theoretical resoanant frequency. How do i make them match? Do i need to take care of something while simulating eigenfrequency analysis.
I am simulating a capacitive micro-accelerometer in comsol. When i perform the eigenfrequency analysis, my eigenfrequencies are way different from the theoretical resoanant frequency. How do i make them match? Do i need to take care of something while simulating eigenfrequency analysis.