substeps and frequency range in harmonic analysis 1

[danshing]

Hello everyone,
I got stuck when I tried to model a two-layered edge-clamped circular membrane to find out its resonant frequency and amplitude. I obtained a plot (displacement vs frequency) by using harmonic analysis and got the resonant fequency where the amplitude has the largest value. However, when I tried to verify the result by defining different harmonic frequency range and different substeps, the value of the amplitude changed although the resonant frequency remained the same.
I appreciate very much if anybody could explain this phenomenon to me.
Another question is which approach can be used to calcuate the bounce back pressure of the membrane.
Thanks a lot.
Dan Shing

 

[Drej]

Do a modal analysis first to see the exact frequency of interest, then make sure you hit that frequency exactly when you do your harmonic analysis.

What you're seeing is a usual spikey response from a forced response analysis. The frequency vs amplitude plot is usually very spikey around the resonant frequencies, and if you don't hit the spikes exact you'll find your amplitudes either side of this frequency can be considerably smaller. To make sure you hit this frequency exact, make sure your harmonic frequencies are caught using the correct NSUBST and frequency range.

Cheers,

-- drej --

 

[danshing]

Thanks a lot Drej.
Another problem remains in my project. Let me give a big picture for the project at first. This model is supposed to be a MEMS Micropump, where the membrane will function as one plate in two parellel plates (like a capacitor). When this capacitor is charged, an electrostatic force will apply to this membrane. An uniform pressure on the top of the surface is applied as well. The membrane will deflect because of the pull-down force and pressure. I would like to calculate how much electrostatic force should be to make the membrane bounce back to the undeformed situation when this force is released (the pressure is permanent). I haven't got an idea how to calcuate it by ANSYS yet. I would appreciate if you or anybody else could give me any suggestions.

Dan Shing

 

[sxv7130]

Hi

I am trying to do a multiphysics (coupled-field) electrostatic-structural analysis in ANSYS. I am trying to model something like the example in the link below.

http://www.ansys.com/industries/mems/mems-application-mirror.asp

I have been trying for a week now but have not been able to get very far. Have not been able to find any tutorials or help in the matter. The ANSYS documentation is not very helpful.

If anybody knows how such simulations are done, or if you help me find a tutorial I would greatly appreciate it.

Thanks