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Zero stress boundary
Posted Dec 13, 2012, 9:12 a.m. EST MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Structural Mechanics 2 Replies
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Hey everyone,
I'm trying to figure out how to model and find the motional eigenfrequencies of a totally free cylinder. That is the requirement as I see it is to have zero stress on all surfaces while still allowing displacements.
Setting all boundaries to free gives modes that have stress on the surfaces, and fixing an internal point helps but still give a solution with finite stress on the surfaces. I have seen mentions of "sharp edge effects" in the forum. Is this my issue do you think?
Thank you
Andreas
I'm trying to figure out how to model and find the motional eigenfrequencies of a totally free cylinder. That is the requirement as I see it is to have zero stress on all surfaces while still allowing displacements.
Setting all boundaries to free gives modes that have stress on the surfaces, and fixing an internal point helps but still give a solution with finite stress on the surfaces. I have seen mentions of "sharp edge effects" in the forum. Is this my issue do you think?
Thank you
Andreas
2 Replies Last Post Dec 17, 2012, 5:36 a.m. EST
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Posted:
1 decade ago
Hi Andreas,
The stresses that you get for the zero frequency rigid body modes should be very small numerical round-off values. Compare against stresses in the first non-rigid body mode.
Nagi Elabbasi
Veryst Engineering
The stresses that you get for the zero frequency rigid body modes should be very small numerical round-off values. Compare against stresses in the first non-rigid body mode.
Nagi Elabbasi
Veryst Engineering
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Posted:
1 decade ago
The stresses that you get for the zero frequency rigid body modes should be very small numerical round-off values. Compare against stresses in the first non-rigid body mode.
Thank you for your answer. I indeed find modes that have a imaginary eigenvalues s.a. -2.55108e11i that seem to only show numerical round-off values of stress while still having a reasonable displacement profile for the mechanical mode. Does this mean I can trust the lambda = -i*2 pi f and f ~ 40 GHz for this mode?
Thank you.