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total surface displacement for simple beam structure
Posted Jul 8, 2015, 12:17 a.m. EDT MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Modeling Tools & Definitions, Parameters, Variables, & Functions, Structural Mechanics 2 Replies
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Greetings,
I am new to comsol.
I am trying to design a simple rectangular beam structure (fixed-end-beam),
to evaluate its resonant frequency and total surface displacement.
I am getting the resonant frequency but I can't get the total surface displacement.
I am using solid mechanics as the physics and eigenfrequency as the study.
I have tried reading several information regarding my problem in this forum, but I still have difficulties to understand it.
I am hoping that somebody can help me.
Thank you so much.
I am new to comsol.
I am trying to design a simple rectangular beam structure (fixed-end-beam),
to evaluate its resonant frequency and total surface displacement.
I am getting the resonant frequency but I can't get the total surface displacement.
I am using solid mechanics as the physics and eigenfrequency as the study.
I have tried reading several information regarding my problem in this forum, but I still have difficulties to understand it.
I am hoping that somebody can help me.
Thank you so much.
2 Replies Last Post Jul 8, 2015, 5:57 p.m. EDT
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Posted:
9 years ago
Hi
Are you doing an eigenfrequency analysis ?
As this solver is there to get the (Eigen)frequencies, but the amplitudes are arbitrary by "design", depending on the normalisation used (RMS by default) there are many threads discussing this, try a search.
An amplitude can only be found in Stationary or Time dependent if you know the load you apply on a given boundary: force, moment or pressure ...
or if its for a resonant frequency, then you need to add the true damping (something tricky to know and somewhat to define) and then you do a Frequency Domain Sweep to get the maximum amplitude for a given damping.
But none (or too low) damping means amplitudes tending towards INF and that is too tough to solve even for COMSOL ;).
--
Good luck
Ivar
Are you doing an eigenfrequency analysis ?
As this solver is there to get the (Eigen)frequencies, but the amplitudes are arbitrary by "design", depending on the normalisation used (RMS by default) there are many threads discussing this, try a search.
An amplitude can only be found in Stationary or Time dependent if you know the load you apply on a given boundary: force, moment or pressure ...
or if its for a resonant frequency, then you need to add the true damping (something tricky to know and somewhat to define) and then you do a Frequency Domain Sweep to get the maximum amplitude for a given damping.
But none (or too low) damping means amplitudes tending towards INF and that is too tough to solve even for COMSOL ;).
--
Good luck
Ivar
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Posted:
9 years ago
As Ivar stated, the displacement modes from an Eigenfrequency analysis gives the eigenfrequencies, but the displacements are relative, albeit normalized.
You must perform a new study and choose Frequency Domain as a preset study.
Then in step 1, and in the Frequencies space, type in a small range of frequencies around the eigen frequency that you are interested. Run the analysis and the default plots generated will chow you the correct (hopefully) surface displacements.
You must perform a new study and choose Frequency Domain as a preset study.
Then in step 1, and in the Frequencies space, type in a small range of frequencies around the eigen frequency that you are interested. Run the analysis and the default plots generated will chow you the correct (hopefully) surface displacements.